3.2 MB
ARMY TM 5-683
APPROVED FOR PUBLIC RELEASE: Distributionis unlimited
This manual has been prepared by or for the Government and is
public property and not subject to copyright.
Reprints or republication of this manual should include a credit substantially as follows: “Joint Departments of the Army, the Navy and
the Air Force, USA, Technical Manual TM 5-683/NAVFAC
MO-116/AFJMAN 32-1083, Electrical Interior Facilities, 30 November
TM 5-683
AFJMAN 32-1083
W A S H I N G T O N , DC, 30 November 1995
Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Codes and specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maintenance requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Priority and scheduling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hazards . . . . . . . . . .. .. ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Periodic maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Metal enclosures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bus bar and terminal connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Under floor ducts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Busways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power circuit breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Network protectors.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Auxiliary switch gear equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Switchgear trouble-shooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Small power transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dry-type transformers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maintenance of electric motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Alternating current (AC) motors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Direct current (DC) motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motor operating considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motor insulation testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motor trouble-shooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functions o motor controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Types of motor controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Components and maintenance of motor controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Preventive maintenance and trouble-shooting guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Visual inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cable insulation testing ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Over potential testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cable trouble-shooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Solid-state maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Solid-state components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electrical disturbances (power quality) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Disturbance measurement and monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Voltage surge suppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ground maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Types of grounding systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ground fault interrupting methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
*This manual supersedesTM 5-683/NAVFAC MO-116/AFM 91-17, dated 2 March 1972
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Lighting maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 1
Fluorescent lighting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 2
Incandescent lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High intensity discharge lighting (HID) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Relamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 6
Lamp trouble-shooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7
Other systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
Emergency and stand-by systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Signal systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Detection systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Monitoring systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Environmental protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Polychlorinated biphenyls (PCBs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...
Lighting ballast. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flammable liquids and gasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Toxic materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Human factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment isolation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2
Switchgear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. . . . . . . . . . . . . . . .
Rotating equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transformers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wiring and testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7
Mechanical . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Danger warnings and fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-9
Personal protective equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1
Volt-ohm-milliammeter (VOM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clamp-on volt-ammeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Harmonic measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-5
Maintenance equipment guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1
Insulation testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-2
Protective relay testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment ground resistance testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System ground resistance testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Battery specific gravity test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
Infrared inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . .
Responsibilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Frequencies and procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
APPENDIX A. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .
9 1
Typical busway installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Drawout circuit breaker positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power circuit breaker main and arcing contacts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Arcing contact gap and wipe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Intermediate contact gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main contact wipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electromechanical trip device time-current curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Typical drawout network protector and enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Network protector removable unit.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Typical contact construction for a network protector..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
2–11. Large cell for a stationary battery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3-1. Dry-type transformer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
4-1. Cutaway view of squirrel-cage induction motor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-2. Cutaway view of wound-rotor induction motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-3. Cutaway view of synchronous motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-4. Primary parts of an AC induction motor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-5. Cleaning and drying motors in place . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-6. Bearing installation precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-7. Construction of ball and roller bearings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-8. Greasing bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-9. Typical sleeve bearings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16
4-10. Cutaway view of a typical DC motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-11. Main types and connections of DCmotors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-12. Armature of a large DC motor on stands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-13. Inspecting and installing brushes on a large DC motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-14. Cutaway section of a commutator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-15. Brush "chatter’’action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-16. Poor commutator conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-17. Good commutator films.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-18. Example of eccentric commutator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-19. Dial gauge to measure commutator concentricity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-20. Common undercutting mistakes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-21. Connections for testing motor insulation resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-1. Manual starters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 2
5-2. Typical magnetic starter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
5-3. Combination starters in NEMA enclosures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-4. Coordination of motor overload relay and current limiting fuse. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-5. Autotransformer starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5-6. Resistance starter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 6
5-7. Part-Winding starter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
5-8. Solid State starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 8
5-9. Typical motor control center . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-10. Cutaway view of typical molded case circuit breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-11. Molded case circuit breaker time-current curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-12. Fuse maintenance practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-13. Underwriters’ Laboratories Cartridge fuse classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-14.Typica l thermal overload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-15. Typical heater selection table for thermal overload device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-16. A NEMA size 6 magnetic contactor (courtesy of Siemens-Allis) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6-1. Connections for testing low voltage cable insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7–1. Typical capacitor types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 3
7-2. Diodes and SCR’s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7–5
7–3. Characteristics of diodes and Zeners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7-4. Testing Zener voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6
7–5. Transistor testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8
8-1. Typical equipment ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 - 3
8-2. Typical grounding system for a building and its apparatus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-3. Methods of system grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-4. Methods o fsolidly grounding the neutral of three-phase systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-5. Methods of resistance grounding the neutral of three-phase systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-8. Grounding for electronic and ADP systems.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-7. Ground fault circuit interrupter operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9-1. Preheat fluorescent lamp andfixture components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9-2. Mercury lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3
9-3. Trouble-shooting fluorescent lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10-1. Sample computer-based fire detection system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10-2. Class A and B fire detection circuits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12–1. Padlock and multiple lock adapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12–2. Typical safety tag. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12–3. Ground cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12-4. Grounding clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12–5. Eye and face protection selection guide.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13-1. Set-up for measuring AC voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-4
13-2. Set-up for measuring resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Set-up for testing phase sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Megohmmeter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..........
Diagram of megohmmeter connections...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......
Comparison of water flow with electric current........... . . . . . . . . . . . . . . . . . . ....
Curves showing components of measured current during insulation testing . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Typical curves showing dielectric absorption effect in a time-resistence or double-reading test . . . . . . . . . . .
Resistive components of a made electrode . . . . . . . . . . . . ..... . . . . . . . . . . . . . . ........
Soil resistivity vs moisture content of red clay soil...... . ...... . . . . . . . . . . .Soil resistance vs temperature of clay soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .
Soil resistance vs depth of electrode..... . . . . . . . . . . . . . . . . . . . . . . . . .. ............
Earth electrode with hemispheres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fall-of-potential method graph. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sampling the cell electrolyte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reading the hydrometer float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
U.S. standard bolt torgues for bus connections heat treated steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trouble-shooting procedures for switchgear equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motor application guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nameplate voltage ratings of standard induction motors . . . . . . . . . . . . . . . . . . . . . . . . . ....
AC synchronous motor trouble-shooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..........
DC motor generator trouble-shooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motor control preventative maintenance guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motor control trouble-shooting chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conductor sizes, insulation thickness, test voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cable maintenance overheating problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...
Power quality problems summary .. ...--. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lamp trouble-shooting guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....
Comparison of fire detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Common trade names for PCB by manufacturers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tools and equipment for effective electrical maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........
Interpreting insulation resistance test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Condition of insulation indicated by dielectric absorption ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Percentage of failure cause since maintained.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment failure rate multipliers vereus maintenance quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interior wiring and lighting system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electric motors and controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TM5-683/NAVFAC MO-116/AFJMAN 32-1083
1-1. Purpose and scope.
This manual provides guidance to facilities maintenance personnel in the maintenance of interior electrical systems of 600 volts and less. These systems
include such components as illumination, low voltage systems, rotating equipment, motor control centers, solid-state equipment, transformers, and
switchgear. It also applies to low voltage controlled
devices on high-voltage systems. The procedures
presented in this manual are basic and can be applied to the equipment of any manufacturer. Detailed information and instructions should be obtained from the instruction book for the particular
type of equipment being serviced.
1-2. References.
Appendix A contains a list of references used in this
1-3. Codes and specifications.
Maintenance on electrical systems and equipment
must adhere to the codes and specifications as they
apply to the work to be performed. Also, manufacturers’ maintenance instructions which accompany
select electrical components must be applied in conjunction with the codes and specifications listed below and the departmental specifications listed in
appendix A.
a. The National Electrical Code [National Fire
Protection Association #70 (NFPA 70)]. This code is
the most widely adopted set of electrical safeguarding practices. It defines approved types of conductors and equipment, acceptable wiring methods,
mandatory and advisory rules, operating voltages,
limitations on loading of conductors, required working spaces, methods of guarding energized parts,
interrupting capacity requirements of system protective and control devices, requirements for connections and splices, insulation resistance requirements, and grounding requirements.
b. Recommended Practice for Electrical Equipment Maintenance (NFPA 70 B).
C . American National Standards Institute/
Institute of Electrical and Electronics Engineers
Standard (ANSI/IEEE Std.) chapter 15, 242-1986,
IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems. This code provides preventive maintenance
practices for electrical systems and equipment used
in industrial-type applications.
1-4. Maintenance requirements.
Preventive maintenance should not be confused
with repairs after a breakdown. The definition of
maintenance implies that the equipment or system
is inspected to discover its weaknesses and then
repair or replace the necessary elements before a
breakdown occurs. A maintenance program for protective devices and the electric system could be divided into the following steps: inspecting, cleaning,
tightening, lubricating, testing, and recording.
a. The effectiveness of the distribution system is
measured in terms of voltage regulation, power factor, load balance, reliability, efficiency of operation,
and costs. To ensure the system’s efficiency, lessen
failures, and maximize safety, an effective maintenance program must be employed. This program
should include and/or consider the following:
(1) Scope of work.
(2) Intervals of performance.
(3) Methods of application.
(4) Safety requirements, practices and procedures.
(5) Adherence to codes, specifications and directives.
(6) Maintenance management procedures regarding tools, records, and follow-up procedures.
(7) Hazards associated with work and the facility.
(8) Emergency operating instructions.
(9) Requirements for periodic review to determine additional loading in circuits such as in family
housing, bachelor quarters, and maintenance and
administrative buildings.
b. A well executed maintenance program will
provide benefits in terms of:
(1) Economic operation.
(2) Improved safety.
(3) Longer equipment life.
(4) Reduced repair and overhaul time.
(5) Fewer unplanned outages.
(6) Early detection of undesirable changes in
the power system.
(7) Improved operation of the facility.
1-5. Records.
A good record keeping system is essential for safe,
efficient and economical operation of electrical facilities and for planning and executing an effective
TM5-683/NAVFAC MO-116/AFJMAN 32-1083
preventive maintenance program. It is recommended to use the Work Information Management
System (WIMS) or other data-automated systems to
keep records rather than paperwork files. Suitable
forms and reports requirements should be developed to suit local needs. When facilities are built,
instruction documents and spare parts lists for all
equipment installed should be obtained prior to
beneficial occupancy acceptance.
a. In addition to charts, work orders, and real
property records, the following records have been
found useful in analysis and correction of recurring
trouble areas.
(1) Diagrams. Accurate single-line and schematic diagrams of the distribution system should be
readily accessible in the electrical shop. These are
essential references when switching circuits and rerouting electric power in emergencies. Such diagrams also provide a simple means of locating facilities and determining the characteristics of electric
supply to buildings requiring maintenance. Electrical personnel must have access to latest "as-built"
building drawings for use in tracing out circuitry
within buildings.
(2) Equipment lists/logs. These lists should be
maintained on all items of equipment such as motors, motor controllers, meters, panelboards, electrical controls, and switchgear. Lists should reflect
detailed information such as the density of all like
items, item ratings and physical locations.
Lists/logs will facilitate scheduling of inspections
and maintenance services.
(3) Equipment maintenance records. These
records should be maintained on every individual
item of electrical equipment that requires maintenance services. Records should include detailed information such as scheduled maintenance and inspection requirements, previous test results,
maintenance repairs performed and any other related information that would facilitate analyzing
the equipment performance. Maintenance records
should be retained on file for as long as needed to
allow collection of sufficient data to perform the
equipment performance analyses. By observing the
equipment performance, downward trends can be
identified and problem areas corrected before major
breakdowns occur.
(4) Emergency operating instructions. Emergency operation of electrical facilities is safer and
quicker when instructions are prepared and posted
in advance. There should be instructions for each
general type of anticipated emergency, stating what
each employee in the electrical section should do,
setting up alternatives for key personnel, and establishing follow-up procedures for use after an emergency has passed. Instructions should be posted in
the electrical shop, security guard office, all emergency generating or operating areas, and other locations as the responsible supervisor deems necessary.
Employees should be listed by name, title, official
telephone number, home address and home telephone number (where permissible). These instructions should emphasize safety under conditions of
stress, power interruptions and similar emergencies.
1-6. Priority and scheduling.
In regard to the support of the installed physical
facilities, it is the policy of the Military Departments that, in order of priority, maintenance should
be second only to operations. It must be systematic
and timely. Subsequent sections in this document
provide generaI suggestions on service frequencies
and procedures. Although these proposed actions
and frequencies may appear to be excessive, these
suggestions are based upon experience and equipment manufacturers’ recommendations. They are
not intended to supersede instructions that electrical manufacturers normally provide. Every realistic
effort should be made to adhere to these suggestions
considering existing manpower levels and available
test equipment. It is generally good practice to inspect equipment three to six months after it is first
put into service and then to inspect and maintain it
every one to three years, depending on its service
and operating conditions. Conditions that make frequent maintenance and inspection necessary are:
a. High humidity and high ambient temperature.
b. Corrosive atmosphere.
c. Excessive dust and dirt.
d. High repetitive duty.
e. Frequent fault interruption.
f. Older equipment.
1-7. Hazards.
Material specifications, construction criteria, installation standards, and safe working procedures
should be applied to minimize hazards. All work
should be performed by qualified electricians and
conform to the latest accepted procedures and standards.
a. Building electrical systems. Fire and safety
hazards in building electrical systems often result
from tampering by unqualified personnel. Probably
the greatest example of tampering is the unauthorized changing or replacing of fuses. Careful observation by maintenance personnel is needed to control excessive use of items such as extension cords,
heaters, air conditioners, and improper grounding
which cause overloading of the wiring system.
Whenever possible, installation of additional receptacles is preferable to the use of extension cords.
TM5-683/NAVFAC MO-116/AFJMAN 32-1083
Each building should be inspected for loose wires,
poor connections, bare conductors, unauthorized or
nonstandard attachment cords, use of wiring or fixtures as support for extraneous items, any conditions likely to cause fires and lamps larger than the
standard size prescribed for outlets.
b. Hazardous locations. Special occupancy areas
include garages, aircraft hangars, gasoline dispensing and service stations, bulk storage plants, and
health care facilities. Such areas designed as "Hazards Locations," as specified in Article 500 of the
National Electrical Code, require special and equipment considerations. These considerations include
the use of special fittings, rigid conduit, and
explosion-proof apparatus. Maintenance personnel
must ensure that all work performed in a hazardous
area complies with the code requirements for the
area’s particular hazard classification.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
2-1. Periodic Maintenance.
A periodic maintenance schedule must be established to obtain the best service from the
switchgear. Annual check should be made on all
major switchgear devices after installation. After
trends have been established regarding the equipment condition and reliability, the maintenance interval may be extended (18–36 months) in keeping
with the operating conditions. A permanent record
of all maintenance work should be kept. The record
should include a list of periodic checks and tests
made (including date of test), condition of the equipment, repairs or adjustments performed, and test
data that would facilitate performing a trend analysis. Maintenance personnel must follow all recognized safety practices, both the nationally published
standards and military regulations. Some specific
suggestions in dealing with switchgear maintenance are given below:
a. Tools designed for slowly closing switchgear
circuit breakers or other devices during maintenance are not suitable for use on an energized system. The speed necessary for device closing is as
important as its speed in opening; therefore, a
wrench or other manual tool is not fast enough.
b. Before working on a switchgear enclosure,
verify that the enclosure is de-energized by checking for voltage using a voltage detector.
c. Disconnect all drawout or tilt-out devices such
as circuit breakers, instrumentation transformers,
and control power transformers.
d. Do not lay tools on the equipment while working. It is all too common to forget a wrench when
closing up an enclosure. Don’t take the chance.
e. Never rely upon the insulation surrounding an
energized conductor to provide protection to personnel. Use suitable safety clothing and equipment.
f. Always use the correct maintenance forms and
equipment. When performing maintenance the following should be available:
(1) Forms for recording the conditions as found
and work done.
(2) Control power connections, test couplers,
and spare parts recommended by the manufacturer
to facilitate repair and maintenance of each type of
circuit breaker.
(3) Special tools, such as lifting mechanisms
for removing and transporting power circuit breakers, relay test plugs for testing and calibrating protective relays, a low resistance ohmmeter for mea-
suring the resistance of contacts, ammeters,
voltmeters, megohmmeters, low voltage/high current test sets for testing power circuit breakers, and
other special test equipment.
(4) Manufacturer’s instruction books regarding
the maintenance of switchgear devices such as circuit breakers, relays, bus bars, meters, etc. The
fundamentals that are presented in the upcoming
sections are designed to supplement these instructions, giving the elements of the overall maintenance program rather than the details.
2-2. Metal enclosures.
Maintenance is recommended below:
a. With power off and the bus properly grounded,
open the enclosure and remove any accumulated
dust and dirt. Vacuum cleaning is recommended;
blowing with compressed air is not.
b. Check structure and anchor bolts for tightness. For bus and breaker connections ensure
manufacturer’s specified torques are used.
c. Clean and lubricate circuit breaker racking
mechanisms with a non-hardening, non-conductive
d. Inspect operation and adjustment of safety
shutters, mechanical and key interlocks, auxiliary
and limit switches.
e. Clean and inspect strip heaters.
f. Clean any air filters that are installed in the
ventilation openings.
g. Inspect all relays, contractors, switches, fuses,
and other auxiliary devices for correct operation
and cleanliness.
h. Tighten control wiring connections.
i. Inspect alignment and contacting of primary
disconnecting devices, checking for signs of abnormal wear or other damage. Discoloration of these or
other silvered surfaces is not usually harmful unless caused by sulphide deposits, which can be removed by a solvent, such as alcohol, or silver polish.
j. After cleaning, measure the resistance to
ground and between phases of the bus with a
megohmmeter (para 14-2). It is not possible to give
definite limits for satisfactory insulation resistance
values, so that a change in the reading from one
inspection period to another is the best indication of
any weakening tendency. The readings should be
taken under similar conditions each time, and the
record should include temperature and humidity.
k. Before replacing the breaker, wipe the primary
disconnecting device contacts. Apply a thin coat of
TM 5-683/NAWAC MO-116/AFJMAN 32-1083
contact lubricant to the stationary studs and to the
primary disconnects on the breaker.
l. Ensure that all metal shields are securely in
place. These shields must be installed to confine any
blast in the event of circuit breaker failure.
(1) A note on lubricants. One of the most useful
lubricants for motors is an extreme pressure (EP)
lithium-base petroleum grease. As the usage of
Class F winding temperature ratings has increased,
however, others have adopted synthetic greases to
withstand higher bearing temperatures.
(2) Synthetic oils and greases. Synthetic oils
and greases compounded from various silicones,
alkyl benzene, diesters, and fluorinated ethers, are
available for extremely high-temperature service
that would cause premature oxidation of petroleum
lubricants. Some synthetics also suit extremely low
temperature, down to 40 or 50 degrees below zero.
The main uses for synthetic lubricants in motor
bearings are reduced friction and resistance to
moisture and chemical contamination. Such applications must be carefully worked out with bearing
and lubricant suppliers, because no universal lubricant formulation will apply to all environments.
However, it is not unusual for lubricant to vary
little more than brand name. Thus substitutions are
often possible. Consult with the manufacturer of the
switchgear to determine the important characteristics of the lubricant prior to specifying a substitute
lubricant. Carefully selected substitutes will reduce
the cost of procurement, stocking and dispensing.
2-3. Bus bar and terminal connections.
Many failures are attributable to improper terminations, poor workmanship, and different characteristics of dissimilar metals. Loose bus bar or terminal
connections will cause overheating which can be
easily spotted by a discoloration of the bus bar. A
thermographic survey can be conducted to detect
overheating before discoloration occurs (para 14-7).
An overheating condition will lead to deterioration
of the bus system as well as to equipment connected
to the bus; i.e. protective devices, bus stabs, etc.
Therefore, bus bar and terminal connections should
be regularly checked to ensure that they are properly tightened without damaging the conductors.
Special attention should be given where excessive
vibration may cause loosening of bolted bus and
terminal connections. Tightening torque values for
electrical connections are provided in table 2–1.
This information should be used for guidance only
where no tightening information on the specific connector is available. It should not be used to replace
manufacturer’s instructions which should always be
followed. Do not assume that once a connection has
been torqued to its proper value that it remains
tight indefinitely. If signs of arcing are evident, then
the connections should be broken and the connecting surfaces cleaned. Because of the different characteristics of copper and aluminum, they should not
be intermixed in a terminal or splicing connector
where physical contact occurs between them, unless
the device is suitable for the purpose and conditions
of use. Materials such as solder and compounds
shall be suitable for the use and shall be of a type
which will not adversely affect the conductors.
a. Aluminum connectors. Special considerations
must be given to aluminum connections. Aluminum
connectors are plated and should not be cleaned
with abrasive. If these connectors are damaged,
they should be replaced. It should be noted that
when making connections with aluminum conductors, be sure to use a joint compound made for the
purpose. To assist in the proper and safe use of solid
aluminum wire in making connections to wiring
devices, refer to the National Electrical Code. Make
aluminum connections with solderless circumferential compression-type, aluminum-bodied connectors
UL listed for AL/CU. Remove surface oxides from
aluminum conductors by wire brushing and immediately apply oxide-inhibiting joint compound and
insert in connector. After joint is made, wipe away
excess joint compound and insulate splice.
b. Bus insulators and barriers. Bus bar support
insulators and/or barriers should be wiped with a
clean cloth. Do not use steel wool or oxide papers to
remove dirt; use a cleaning solvent that will not
leave trace deposits. While cleaning, check insulators for cracks and signs of arc tracking. Defective
units should be replaced. Loose mounting hardware
should be tightened.
2-4. Underfloor ducts.
All undefloor duct systems require checks for evidence of oil and water. Entrances and fittings
should be checked and corrected as necessary to
prevent entrance of liquids, insects, and rodents.
Cockroaches, ants, beetles and rodents have been
known to attack cable insulation, especially if
greases or oils are present. External heat and heat
caused by overloaded circuits can cause cracking of
cable insulation and drying of taped splices. Moisture can then penetrate the cable and could cause a
fault. Therefore, underfloor conduits and duct systems should be kept sufficiently clear of electrical
and hot water floor-heating systems to prevent undue heating of the enclosures.
2-5. Busways.
Feeder busway, trolley busway and plug-in busway
(fig 2–1) require annual cleaning and removal of oil
substances and dirt. Ventilated-type busway should
TM 5-683/NAWAC MO-116/AFJMAN 32-1083
have the bus bars cleaned annually with clean, dry
compressed air at a maximum pressure of 50
pounds per square inch. Plug-in devices should be
serviced using the same procedures as other
switches or breakers. The plug-in bus or prongs
should be checked annually for annealing or corrosion on all connections which are rated in excess to
75 percent of the rating of the bus duct. Connections
should not be retorqued as part of a routine maintenance procedure unless visibly loose or shown to
be loose by an infrared scan. All busway connections
should be torqued according to manufactures recommendations. If this information is not available,
use the torque specifications in table 2-1. Inspect to
ensure that:
a. Ventilation continues to be adequate.
b. Clearances are maintained and encroachment
from other equipment facilities has not occurred.
2-6. Power circuit breakers.
Power circuit breakers encompass all breakers except molded case breakers and breakers used for
control applications. It is recommended that power
circuit breakers be inspected once a year after installation. More frequent inspections are recommended where severe load conditions, dust, moisture or other unfavorable conditions exist, or if the
vital nature of the load warrants it. Any breaker
that has interrupted a fault at or near its short
circuit rating should be inspected immediately after
the interruption and serviced if necessary. Reenergize equipment completely before working on
any devices, connections, bus work, breaker or
feeder cable compartments. This includes deenergizing any connections to outside primary or
secondary sources such as transformers, tie lines,
etc. Manufacturer’s instruction documents should
also be obtained and read carefully before disassembly or adjustments are performed.
a. Drawout circuit breakers. A drawout-type
breaker should be tested and inspected for proper
operation as follows:
(1) Withdraw the breaker to the “test” position.
This position disconnects the primary power circuit
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 2-1. Typical busway installation.
but leaves the control circuits energized (fig 2-2). If
a “test” position is not provided, then completely withdraw the circuit breaker from its compartment and use a test coupler to provide control
(2) Test for voltage to make sure that all paths
of potential backfeed from control power circuits, as
well as outside sources, are disconnected. This is
especially important if an external source of control
power is being used for testing.
(3) Operate the breaker and check all functions. Use both the electrical means (when pro2-4
vided) and the mechanical means to charge, close
and trip the breaker. This is particularly important
for breakers that normally remain in either the
opened or closed position for long periods of time.
(4) Remove the breaker from its compartment
to a clean maintenance area. Close the compartment door and cover the breaker cutout to prevent
access to live parts.
(5) Check and lubricate all safety rollers and
auxiliary contacts. Check all mechanical clearances
to ensure they are within manufacturer specified
tolerances. Also inspect and lubricate bus stabs and
TM 5-683/NAVFAC M116/AFJMAN 32-1083
Figure 2-2. Drawout circuit breaker positions.
ac/dc control block contacts. Verify correct operation
of “trip free” and anti-pump mechanisms.
b. Fixed circuit breakers. Maintenance on fixedor bolter-type circuit breakers is normally performed with the breaker in place inside its cubicle.
Special precautions must be exercised to assure
equipment is de-energized and the circuit in which
it is connected is properly secured from a safety
standpoint. All control circuits should be deenergized. Stored energy closing mechanisms
should be discharged.
c. Power circuit breaker components. Maintenance on all power circuit breakers will encompass
maintenance on the following components.
(1) Insulation. The general rule for insulation
is keep it clean and dry. Remove interphase barriers
and clean them and all other insulating surfaces
with dry compressed air and a vacuum cleaner.
Wipe insulation with clean lint-free rags and solvents as recommended by the manufacturer if hardened or encrusted contamination must be removed.
Repair moderate damage to bushing insulation by
sanding smooth and refinishing with a clear insulating varnish. Check insulating parts for evidence
of overheating and for cracks that indicate excessive
thermal aging.
(2) Contacts. The major function of the power
circuit breaker depends among other things upon
correct operation of its contacts. These circuit
breakers normally have at least two distinct sets of
contacts on each pole, main and arcing (fig 2-3).
Some have an intermediate pair of contacts which
open after the main contacts and before the arcing
(a) Main contacts. When the breaker is
closed, practically the entire load current passes
through the main contacts. Also, short circuit current must pass through them during opening or
closing faulted lines. If the resistance on these contacts becomes high, they will overheat. Increased
contact resistance can be caused by pitted contact
surfaces, foreign material embedded on contact sur-
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 2-3. Power circuit breaker main and arcing contacts.
faces, or weakened contact spring pressure. This
will cause excessive current to be diverted through
the arcing contacts, with consequent overheating
and burning.
(b) Arcing contacts. Arcing contacts are the
last to open; any arcing normally originates on
them. In circuit interruption, they carry current
only momentarily, but that current may be equal to
the interrupting rating of the breaker. In closing
against a short circuit, they may momentarily carry
considerably more than the short circuit interrupting rating. Therefore, they must make positive contact when they are touching. If not, the main contacts can be badly burned or may result in a failure
to interrupt a fault.
(c) Contact maintenance. The general rules
for maintaining contacts on all types of breakers
are: keep them clean, aligned and well adjusted. To
inspect the circuit breaker contacts, the arc chutes
must be removed. When doing this, check the arc
chutes for evidence of damage, and replace damaged parts. If not damaged, then blow off dust or
loose particles. Once the main contacts are exposed,
inspect their condition. Slight impressions on the
stationary contacts caused by the pressure and wiping action of the movable contacts is tolerable. Contacts which have been roughened in service should
not be filed but large projections, caused by unusual
arcing, should be removed by filing. When filing,
take care to keep the contacts in their original de-
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
sign. That is, if the contact is a line type, keep the
area of contact linear, and if ball type, keep the ball
shaped out. Discoloration of silver-plated surfaces is
not usually harmful unless caused by insulating
deposits. These deposits should be removed with
alcohol or a silver cleaner. Whether cleaned or not,
lubricate the main contacts by applying a thin film
of slow aging, heat resistant grease. All excess lubricant should be removed with a clean cloth to avoid
accumulation of dirt and dust. Under no circumstances should the arcing contacts be lubricated.
Where serious overheating is indicated by discoloration of metal and surrounding insulation, the contact and spring assemblies should be replaced in
accordance with manufacturer’s instructions. While
carefully closing the circuit breaker, check for
proper gap, wipe and contact alignment. Contact
gap is the distance between the stationary and movable contacts with the circuit breaker in the fully
open position. If the arcing contact gap is too small,
a circuit breaker may not be able to interrupt a
fault. If the main contact gap is too small, the main
contacts will interrupt the fault along with the arcing contacts and possibly burn the main contacts.
Contact wipe is the amount of over travel between
the stationary and movable contacts from the time
when the contacts are just touching to the time
when the circuit breaker is fully closed (figs 2–4,
2–5, and 2–6). Check that all contacts make and
break at approximately the same time. Make adjustments in accordance with the manufacturer’s
recommendations. Laminated copper or brush style
Figure 2-4. Arcing contact gap and wipe.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 2-5 Intermediate contact gap.
contacts found on older circuit breakers should be
replaced when badly burned. Repairs are not practical because the laminations tend to weld together
when burning occurs, and contact pressure and
wipe are greatly reduced. These contacts may be
filed to remove large projections or to restore their
original shape. They should be replaced when they
are burned sufficiently to prevent adequate circuit
breaker operation or when half of the contact surface is burned away. Carbon contacts, used on older
circuit breakers, require very little maintenance.
However, inadequate contact pressure caused by
erosion or repeated filing may cause overheating or
interfere with their function as arcing contacts.
(3) Operating mechanism. The purpose of the
operating mechanism is to open and close the
breaker contacts. This usually is done by linkages
connected, for most power breakers, to a power operating device such as a solenoid or closing spring
for closing, and contains one or more small solenoids or other types of electro-magnets for tripping.
Tripping is accomplished mechanically, independent
from the closing device, so that the breaker contacts
will open even though the closing device still may be
in the closed position. This combination is called a
mechanically trip-free mechanism. After closing,
the primary function of the operating mechanism is
to open the breaker when it is desired, which is
whenever the tripping coil is energized at above its
rated minimum operating voltage. The breaker operating mechanism should be inspected for loose or
broken parts; missing cotter pins or retaining keepers; and missing nuts and bolts. It should also be
examined for damage or excessive wear on cam,
latch, and roller surfaces. Excessive wear usually
results in loss of travel of the breaker contacts. It
can affect operation of latches; they may stick or
slip off and prematurely trip the breaker. Adjust-
TM 5+583/NAVFAC MO-1 16/AFJMAN 32-1083
Figure 2-6. Main contact wipe.
menta for excessive wear are possible for certain
parts. For others, replacement is necessary. The
closing and tripping action of a breaker should be
quick and positive. While documenting, operate the
breaker several times, checking for obstructions or
excessive friction. Any binding, slow action, delay in
speration, or failure to trip or latch must be conrected prior to returning to service. Clean and
relubricate the operating mechanism. Use a
nondetergent light machine oil (SAE-20 or 30) to
lubricate pins and bearings not disassembled. Use a
non-hardening and non-conductive grease to lubncate the ground or polished surfaces of cams,
rollovers, latches and props, pins and bearings that
are removed for cleaning. Check the breaker operating mechanism adjustments and readjust as described in the manufacture% instruction book. If
these adjustments cannot be made within specified
tolerances, it will usually indicate excessive wear
and the need for a complete overhaul.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(4) Trip devices. The trip devices on low voltage
circuit breakers provide the electrical decisions
needed to detect the difference between normal and
abnormal conditions of current flow. The maintenance and adjustment of these devices is just as
important as the work performed on the main contacts and operating mechanism. The trip devices
are either electro-mechanical or solid-state. Both
types are responsible for providing various degrees
of fixed, short, or inverse time delays based on the
amount of current they sense. The electromechanical type, with an air or fluid dashpot for
time delay, should be tested as part of the maintenance work performed. A dashpot is a pneumatic or
hydraulic device used for cushioning or damping of
movement to avoid mechanical shock and consisting
essentially of a cylinder containing air or liquid and
a piston moving in it. Testing of the electromechanical devices requires the use of a low voltage
(about 0-20V) but high current (usually O50,000A) primary injection test set designed specifically for this purpose. Calibration tests should be
made to verify that the performance of the device is
within the values shown on the manufacturer’s published curves; taking into account that the timecurrent curves are plotted as a band of values
rather than a single line (fig 2–7). Pay careful attention to how the manufacturer has presented the
curve data. There is a wide variety of formats.
Check to see that the current is in amperes or multiples of a pickup value and whether temperature
ranges or previous conditions will affect results.
Usually, the trip devices are tested one unit at a
time. There are some devices which may use a thermal element for time delay. These may have to be
tested all at once to get results similar to those
published by the manufacturer. Check the test conditions carefully. If the trip devices do not operate
properly, the calibration and timing components
should be adjusted or replaced per the manufacturer’s recommendations. If repair or replacement of
the electro-mechanical devices is being considered,
then thought should be given toward retrofitting
the existing breaker with solid-state trip devices.
This newer technology is generally more reliable
because the parts used to make the trip unit do not
drift out of adjustment or suffer the effects of aging
or contamination to the same degree as their
electro-mechanical forerunners. If the breakers are
already equipped with solid-state trip devices, they
should also be checked for proper operation and
time delay in accordance with the manufacturer’s
published curves. The test procedure recommended
by the manufacturer should be followed.
(5) Auxiliary devices. Inspect the closing motor
or solenoid, shunt trip coil and mechanism, alarm
mechanisms, and the control wiring for correct operations, insulation condition and tightness of connections. Check on-off indicators, spring-charge indicators, mechanical and electrical interlocks, key
interlocks, and lock-out fixtures for proper operation and lubricate where required. In particular,
test the positive interlock feature which prevents
the insertion or removal of the breaker while it is in
the closed position. Check control devices for freedom of operation. Replace contacts when badly worn
or burned. After the breaker has been serviced,
manually operate it slowly with a closing device to
check for tightness or friction and to see that the
contacts move to their fully open and fully closed
positions. Electrically operate the breaker several
times to check the performance of the electrical accessories using the “TEST” position, an external
test/control cabinet, or a test coupler.
2-7. Network protectors.
The current-carrying parts, main contacts, and operating mechanism of a network protector are very
similar to those of the air circuit breaker. This similarity usually ends with the principal mechanical
devices. Unlike the usual feeder circuit breaker, the
network protector is more like a tie circuit breaker;
that is, it is almost always energized on both sides.
This condition requires that extreme care be taken
during installation or removal of the unit from service. The network protector is equipped with special
relays that sense the network circuit conditions and
command the mechanism to either open or close
automatically in response to those conditions. Network protectors are used where large amounts of
power must be distributed to high density load areas such as commercial buildings and office complexes. To form a network, several incoming power
sources may be connected. As a result, a short circuit at any point in the system usually involves very
high fault currents.
a. Safety precautions. Due to the construction
and purpose of the network protector, taking it out
of service or placing it back in service is a procedure
that must be done while the circuit is energized.
During this work, always use the special insulated
tools provided with the particular model to be serviced. Alternate or make-shift tools are not recommended unless they have been laboratory tested
and are known to have good safety performance.
Electrical grade, safety gloves should still be worn
by the person servicing the unit regardless of the
type or condition of the tools used.
b. Maintenance. A routine maintenance schedule
for network protectors should be observed. The frequency of inspection will vary based on the location
and environment in which the unit is installed, and
TM 5483/NAVFAC MO-116/AFJMAN 32-1083
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TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
the number of operations the unit has made. In all
cases, open the circuit first. This is done by moving
the control handle from “AUTOMATIC” to
“MANUAL” and then manually opening the circuit.
The control handle and/or operating mechanism
should then be locked in the “OPEN” position before
further work is done. Maintenance should include
cleaning any accumulation of dust, dirt or corrosion
deposits, a thorough visual inspection, and overall
performance tests. Should the operation of any part
be suspect, refer to the manufacturer’s instructions
describing operation, adjustment, and replacement
of these parts. If the network sensing relays are out
of calibration, they should be recalibrated by competent shop personnel. The network protector is
housed in a cell or enclosure similar to those used
for air circuit breakers (fig 2-8). The circuit breaker
mechanism and the network relay panel assembly
of a network protector are usually constructed aa an
integral, drawout unit which must be withdrawn
fmm the housing for proper maintenance. Removal
is done by unbolting the fuses at the top (usually)
and the disconnecting links at the bottom (some
models have bolt-actuated disconnecting fingers at
the bottom). After removing any additional lockdown bolts or latches, the drawout unit may be
carefully withdrawn using the rails provided for
support. Although this provides a comparative
measure of safety, work should be done cautiously
since there is voltage present within the enclosure.
It is better to move the unit completely away from
the enclosure (fig 2–9). The following inspection and
maintenance operations can be done on the drawout
(1) Clean the breaker assembly. Use of a
vacuum cleaner is preferred. Use cloth rags free of
oil or grease for removing clinging dirt.
(2) Remove arc quenchers. Replace if damaged.
(3) Inspect main contacts (fig 2-10). Smooth
any heavily frosted area with a very fine file or a
burnishing stone which does not shed abrasive particles. Protect hinged joints from falling particles
during filing.
(4) File smooth any especially high projections
of metal on arcing contacts.
(5) See that all electrical connections are tight.
(6) Look for any abrasion of wire insulation
and repair.
(7) Check for signs of overheating of control
wire and current carrying parts.
(8) See that all springs are in good condition
and are properly seated in place.
(9) See that all nuts, pins, snap rings or retainers, and screws are in place and tight.
(10) Replace any broken or missing barriers.
(11) With the rollout unit still set aside, perform the following maintenance operations inside
the enclosure:
Both source and load terminals are probably still energized. Use insulated tools and safety
protective equipment for this work. Do not remove any barriers from the enclosure.
(a) Look for loose hardware on the enclosure
bottom or beneath the frame. If any is found, trace
to source and correct problem or replace.
(b) Clean stand-off bus insulators.
(c) Remove oxide film from terminal contacts
if necessary.
(12) Manually close and trip the breaker
mechanism according to instructions furnished for
the particular model.
(13) Perform an operational test using a network protector test kit.
(14) Conduct insulation resistance tests, dielectric test and electrical operating test in accordance with the manufacturer’s recommendations.
(15) Carefully replace the drawout unit in the
enclosure. Make a final inspection to be sure no
control wiring has become snagged, and that no
plugs or connecting surfaces have been bent or damaged.
2-8. Auxiliary switchgear equipment.
Auxiliary equipment includes devices such as fuses,
capacitors, meters, relays, etc. This equipment
should be serviced along with the major switchgear
components, unless there is some indication that a
device is being heavily or improperly used, in which
case it should be inspected more often. Protective
relays and meters should be inspected and calibrated on a scheduled basis. Critical service equipment should have the protective relays checked at
every maintenance turn (annually or according to
manufacturer’s recommendations). Relays applied
to other general distribution circuits may be done
less frequently (see para 2-8h).
a. Fuses. Fuse maintenance is covered as a separate category of electrical equipment (para 5-4d).
b. Capacitors. The maintenance requirement on
power capacitor installations is so small that its
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 2-8. Typical drawout network protector and enclosure.
( Two On
Each Side
Figure 2–9. Network protector removable unit.
importance is often overlooked. The voltage of the
system at the capacitor location should be checked
at light load periods to determine if an overvoltage
condition exists. Any changes in circuit connections,
which may increase voltage levels, warrant a re-
check of operating conditions. The conductor sizes
should provide for not less than 135 percent of capacitor current at rated voltage and WA. As a general rule, if the side of the capacitor unit casing is
operating at a temperature above 55 degrees C (131
degrees F a temperature almost too hot for barehand contact), then a more complete investigation
of operating conditions should be made. The case
temperatures should never exceed 65 degrees C
(149 degrees F) under any conditions. Adequate
ventilation is therefore necessary to remove the
heat generated by continuous full-load duty. Remove any obstructions at ventilation openings in
capacitor housings to ensure that this ventilation is
maintained. A disconnected capacitor retains its
electrical charge for some time and may even retain
the full-line voltage across its terminals. Therefore
always discharge a capacitor before handling or
making connections. An insulation short circuit
jumper may be used for this purpose; however, it
should only be applied with full knowledge of the
circuit, and with the use of appropriate protective
equipment. Power capacitors are generally provided
with individual fuses to protect the system in case
of a short circuit within the capacitor. In addition to
a faulty capacitor, a fuse may be blown by an abnormal voltage surge. Check for blown fuses and replace them with a type recommended by the manufacturer. Do not remove fuses by hand until the
capacitor has been completely discharged. Clean the
case of a capacitor, the insulating bushings, and any
TM 5-683/NAVFAC MO-1 16/AFJMAN 32-1083
Figure 2–10. Typical contact construction for a network protector.
connections that are dirty or corroded. Inspect the
case of each capacitor for leaks, bulges, or discoloration. If any of these conditions exist, then replace
the capacitor (para 11–2).
c. Battery supplies. The control battery is such an
important item in switchgear operation that it must
be given strict attention in the maintenance program. The battery charger plays a critical role since
it supplies normal direct current (DC) power to the
station and maintains the batteries at a high level
of charge. The batteries, in addition to supplying
temporary heavy demands in excess of the charger
capacity, serve as a back-up source to trip breakers
upon loss of alternating current (AC) power. Failure
of the charger or its AC supply transfers all DC load
to the batteries. Each battery cell electrolyte level
should be checked. While a single cell may not produce a serious shock hazard, when the cells are
connected in a battery bank, a severe shock hazard
may be possible. Also, there are usually many ex2-14
posed connections, and safety gear and tools must
be used to the best degree of safety such as face
shields, acid/caustic resistant gloves, emergency
eyewash, etc. Electrolyte is the fluid contained in
each battery cell (fig 2–11). Low electrolyte levels
indicate too high a charging rate. In this case, the
“float-voltage” setting of the charger should be
checked against the battery manufacturer’s recommendations. The specific gravity of the battery electrolyte should be taken using a hydrometer (para
14-6). If the readings between battery cells vary
more than fifty points on the hydrometer scale, the
battery probably has a bad cell which should be
replaced. If all cells read consistently low (within 50
points), the battery should be fully charged and the
battery charger checked for proper operation. The
battery top surface should be clean. Surface contamination can produce leakage currents that
present a drain on the charger and the battery. Vent
holes in the cell caps should be open. Battery termi-
TM 5-683/NAVFAC MO-1161AFJMAN 32-1083
nal connections should be tight and free of corrosion. If the terminal connections are corroded, they
should be cleaned with bicarbonate of soda. Battery
terminals and cable ends should be cleaned thoroughly. If stranded cable is used it is advisable to
cut off the corroded end. If this is not possible, the
strands should be separated and cleaned internally.
Any dust accumulation on the battery charger
should be blown off or wiped clean. Ventilation
openings should be clear of obstruction. Terminal
connections should be checked for tightness. All relays, lights or horns for indicating such abnormal
conditions as grounds, loss of AC power supply, and
high or low voltage should be checked to ensure that
they are operating properly. During maintenance
outages of the AC supply, there may be times when
it is necessary to provide a temporary supply to the
charger. While being charged, a battery produces
and emits a mixture of hydrogen and oxygen gases
which is very explosive. Open flames or sparks must
not be permitted in close proximity to the batteries.
The room or compartment in which operating batteries are located should be well ventilated. Smoking should be prohibited in these rooms or compartments.
d. Instrument transformers. Instrument transformers are used to step down a current or voltage
in order to operate a meter or a relay. Indoor-type
instrument transformers are normally dry type, except potential transformers (PTs) which may be enclosed in compound-filled metal cases. The more
common transformer constructions have the complete transformer molded into one solid mass with
only the terminals exposed.
I Never open circuit the secondary winding** ofCAUTION**
a current transformer while energized. To do so
may result in component damage or personal injury.
Figure 2-11. Large cell for a stationary battery.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(11) Verify connection of secondary PT leads by
applying a low voltage to the leads and checking for
voltage contribution at applicable devices.
(12) Check for PT secondary load with secondary voltage and current measurements. Make sure
load is less than volt amps (VA) of PT.
f. Metering. Most of the buildings in a typical
military installation are unmetered. Meters (both
recording and indicating), relays, and associated
equipment are usually part of a substation, main
distribution switchboard equipment, or special
equipment. Industrial shops and other buildings occasionally utilize kilowatt hour demand meters,
power factor meters, ammeters, and voltmeters. In
an effort to determine whether the maintenance or
operation of these meters is adequate demands that
the metering instruments be of the specified range,
accurately calibrated, and adequately serviced. Instrument accuracy is always expressed in terms of
the percentage of error at the full-scale point. Maximum accuracy, consequently, is obtainable by keeping the rating as high on the scale as possible, and
requires a properly rated instrument. An instrument with an accuracy of 1 percent, with a scale
reading of 100 divided into 100 divisions, is accurate
to plus or minus one division. Hence, a reading of 20
has a margin of error of plus or minus one division,
which in this instance means that the true value
could be between 19 or 21—an actual variation of 10
percent. If the maximum indicating meter reading
is less than 50 percent of the meter range, indicating meters should be recalibrated, and ratchets and
dials changed. How often an instrument is calibrated depends on its use and the desired accuracy.
If calibration standards and equipment are not
available, instruments of nearly the same rating
may be checked against each other. If wide discrepancies are noted, the suspect instrument should be
checked by a competent laboratory or returned to
the manufacturer. For many military establishments, the utility company will best perform this
work. Take care to prevent entrance of dirt or lint
into an instrument because this dirt could hinder
the actuation of the instrument pointer. Clean the
glass with a damp cloth because a dry cloth may
induce a static charge on the glass and affect the
instrument reading. Breathing on a charged glass
discharges it. Never oil instrument bearings. Indicating demand and power factor meters should be
tested and recalibrated every 2 years. Single-phase
watt hour meters should be tested at least once
every 5 years; self-contained polyphase watt-hour
meters every 2 years. Transformer watt-hour
meters on the secondary system (600 volts and below) should also be tested every 2 years; transformer watt-hour meters on the primary system
every year. Voltmeters and ammeters should be calibrated at 2-year intervals.
g. Alarms. Alarms associated with transformer
overtemperature, high or low pressure, circuit
breaker trip, accidental ground on an ungrounded
system, cooling water flow or overtemperature, or
other system conditions should be tested periodically to assure proper operation.
h. Indicators. Circuit breaker “open-close” indicators can be checked during their regular maintenance. Ground indicator lamps for ungrounded electric systems should be checked daily or weekly for
proper operation. Other miscellaneous indicators
such as flow, overtemperature, excess pressure, etc.,
should be checked or operated periodically to assure
proper operation.
i. Protective relaying. While the application of circuit protection as developed in a short circuit and
coordination study is an engineering function, assurance that this designed protection remains in
operation is a maintenance responsibility. Applying
relay settings and periodically testing them are
maintenance functions. Relays should be examined
to ensure the following:
(1) All moving parts are free of friction or binding.
(2) All wiring connections are tight.
(3) All contacts are free of pitting or erosion.
(4) solenoid coils or armatures are not overheated.
(5) Glass, covers or cases are not damaged.
j. For relay testing procedures, refer to chapter 14.
The protective relay circuitry should also be
checked by closing the breaker in the test position
and while documenting, closing the contacts of each
protective relay to trip the circuit breaker.
2-9. Switchgear trouble-shooting.
Table 2–2 provides detailed information regarding
trouble-shooting switchgear failures. Probable
causes along with recommended remedies are listed
for typical failures.
TM 5-683/AVFAC MO-116/AFJMAN 32-1083
Table 2-2. Trouble-shooting procedures for switchgear equipment.
Meters Inaccurate
Dirt or dust may be impeding
movement; particles may be
adhering to the magnets
C l e a nr t e s t a n d c a l i b r a t e m e t e r .
Meter may be damaged - have a
cracked jewel, rough bearing,
bent disk or shaft,
insufficient disk clearance or
damaged coils.
Repair or replace damaged parts,
test and calibrate meter.
Tighten test and calibrate meter.
Loose connections.
Remove the short.
C.T. circuit shorted or
shorting strap left
Meters Failing to Register
Blown potential transformer
Renew blown fuses. A s c e r t a i n r e a s o n
and correct trouble.
Repair break, c o r r e c t f a u l t .
Broken wires or fault in
Wedge or block accidentally
left at time of test or
Remove wedge or block, test and
calibrate meter.
Remove the short.
C.T. circuit shorted or
shorting strap left.
Damaged Control, Instrument
Transfer Switch or Test Blocks
Burned or pitted contacts from
long use without attention or
from unusual conditions.
Dress or clean burned contacts, or
replace with new contacts if
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 2-2. Trouble-shooting procedures for switchgear equipment - continued.
Relays Failing to Trip
Improper setting.
Dirty, corroded or tarnished
Adjust setting to correspond with
circuit conditions.
Clean contacts with burnishing tool.
Do not use emery or sandpaper.
Readjust so that contacts close with
proper amount of wipe.
Contacts improperly adjusted.
Open circuits or short
circuits in relay connections.
Check with instruments to a s c e r t a i n
that voltage is applied and that
current is passing through relay.
Target and holding coils should
correspond with tripping duty of
breaker to assure proper tripping.
Improper application of target
and holding coil.
If timing device is of bellows or
oil-film type, clean and adjust. If
of induction-disk type, check for
mechanical interference.
Faulty or improperly adjusted
timing devices.
Noises Due to Vibrating Parts
Loose bolts or nuts permitting
excessive vibration.
Loose laminations in cores of
transformers. reactors, etc.
Tighten any loose nuts or core
Connections Overheating
Increase of current due to
additional load that is beyond
normal current rating of bars
or cables.
Increase the number or size of
Remove excess current
from circuit.
Bolts and nuts in the
connection joints not tight.
Tighten all bolts and nuts. Too
much pressure must be avoided.
TM 5-683 /NAVFAC M-116/AFJMAN 32-1083
Table 2-2. Trouble-shooting procedures for switchgear equipment - continued.
Failure in Function of All
Instruments and Devices Having
Potential Windings
Loose nuts, binding screws or
broken wire at terminals.
Tighten all loose connections or
repair broken wire circuits.
Blown fuse in potential
Renew fuses.
Open circuit in potential
transformer primary or
Repair open circuit and check entire
circuits for intactness and good
transformer circuit.
Remove the short.
C.T. circuit shorted or
shorting strap left.
Breaker Fails to Trip
Mechanism binding or sticking
due to lack of lubrication.
Mechanism out of adjustment.
Adjust all mechanical devices, such
as toggles, stops buffers, opening
springs, etc., according to
instruction book.
Failure of lacking device.
If worn
Examine surface of latch.
or corroded, it should be replaced.
Check latch wipe and adjust
according to instruction book.
Replace damaged coil.
Damaged trip coil.
Replace blown fuse.
Blown fuse in control circuit
(where trip coils are
potential type).
Faulty connections (loose or
broken wire) in trip circuit.
Repair faulty wiring. See that all
binding screws are tight.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
3-1. Small power transformers
Transformers referred to herein are limited to those
having a primary voltage under 600V usually of
dry-type construction and are used for lighting, control power, and small power applications. These
small power transformers sometimes supply power
to loads where continuity of service is critical and
therefore a greater degree of attention is justified.
While the percentage of transformer failures is low,
failures that do occur are serious and result in extensive downtime and expense. The best assurance
of continued high reliability is regular maintenance
procedures. A transformer is a device usually used
to transform, or step down a higher distribution
level voltage to a lower utilization level. Although
among the most reliable components in an electrical
system, proper transformer maintenance is still a
necessity. While removal of a transformer from service cannot always be accomplished, visual inspections and testing can be performed with the transformer in service. Transformers require very little
attention when compared to most electrical apparatus. The extent of the inspection and maintenance
will be governed by the size, the importance of service community, the location on the system, and
operating conditions such as, ambient temperature
and the surrounding atmosphere. In general, a twoyear maintenance cycle is appropriate (see para
15-3 for transformers).
3-2. Dry-type transformers.
Dry-type transformers are of open-or-ventilated
type construction with either air or gas serving as
the insulation medium.
a. Routine inspections. All measurements should
be taken at the time of peak load and recorded so
that a means of comparing existing versus previous
transformer conditions is available. Routine inspections of dry-type transformers should include load
current readings, voltage readings and ambient
temperature readings.
(1) Load current readings. If load current readings exceed the rated full load current of the transformer, then steps should be taken to reduce the
load to within design limits.
(2) Voltage readings. Either undervoltages or
overvoltages can be detrimental to a load and/for the
transformer. If one of these conditions exists, then
its cause should be determined and corrected to
within nominal nameplate values.
(3) Ambient temperature readings. Dry-type
transformers are cooled by free circulation of surrounding air over their surfaces. In a totally enclosed transformer, all heat is transferred by the
exterior surfaces; an encased transformer depends
upon air to enter the case at the bottom, flow upward over core and coil surfaces, and flow out of the
case at the opening near the top. These transformers will perform satisfactorily at rated output when
surrounding air does not exceed 40 degrees C (104
degrees F) and adjacent structures permit free
movement of cooling air. Dry-type transformers are
designed to reach rated temperature rise above ambient air temperature when operating continuously
at rated voltage, frequency, or load. Serious overheating may result if the unit is operated for sustained periods at above rated voltage, above rated
current, or at lower than rated frequency. Operating
a transformer above the recommended temperature
will shorten the life of the solid insulation and subsequently increase the risk of a failure. Therefore,
it’s important that ambient temperature readings
be taken at the transformer to verify that it is
within its design limits. If these limits are exceeded,
simply moving the transformer to a cooler environment or providing additional ventilation or removing structures that prohibit the flow of cool air
around the transformer may correct overtemperature conditions. If these changes are not feasible
then the load on the transformer needs to be reduced or a higher rating transformer installed.
b. Special inspections. Before any work, more extensive than a visual inspection is performed on a
transformer, it must be de-energized, tagged and
locked-out (para 12–2). This is to ensure the safety
of both personnel and equipment. In general, drytype transformers have no moving parts (fig 3–1).
The only maintenance required is periodic tightening of connections and removal of accumulated dust,
dirt and lint as outlined below:
(1) Check for dirt accumulation on windings,
internal leads and insulating surfaces.
(2) Check for dirt accumulation that impedes
the flow of cool air.
(3) Check for tracking and carbonization over
insulating surfaces.
(4) Check for cracked or loose insulators or coil
(5) Check deterioration of the turn insulation
and barrier cylinders.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(6) Check for corrosion at all primary, secondary, tap, and ground connections.
(7) Check for loose connections at the coil
clamps, primary, secondary, tap, and ground connections.
c. Repairs. A transformer should be cleaned of
dirt and dust annually with a vacuum cleaner,
blower or air compressor at less than or equal to 30
PSI. If moisture is evident by the appearance of
rust, the unit should be dried by placing it in an
oven or by blowing heated air over it. Liquid cleaners may only be used if recommended by the manufacturer. It should be noted that if any inspection
and/or repair that takes longer than 24 hours or
allows the transformer to cool to ambient temperature, then special drying procedures outlined by the
manufacturer should be adhered to before the
transformer is re-energized.
Figure 3–1. Dry-type transformers.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
4-1. Maintenance of electric motors.
This information is intended to aid personnel concerned with the maintenance of electric motors. The
data provided cover all DC and AC motors. The
recommendations are general in nature and normally can be applied to the type of motors found on
military installations. They are not intended to
cover in detail the specialized applications occasionally encountered. For such cases, the manufacturer’s instructions should be followed. Periodic inspection and regularly scheduled preventive maintenance checks and services will enhance continuous operation of the equipment without undue
breakdowns. Frequency of these inspections often
depends upon elements such as the criticality of the
service, hours equipment is normally in service, and
environment under which the equipment operates.
In order to ensure an accurate data base from which
an effective maintenance program can be initiated,
a complete listing of machines in operation, the
functions they perform and past history of operation
and maintenance services must be maintained. Motor inspection and scheduled maintenance in the Air
Force is performed by the work center responsible
for the system (HVAC, sewer plant, water plant,
etc.). Preventive maintenance will generally involve
lubrication, cleaning and checking for sparking
brushes, vibration, loose belts, high temperature,
and unusual noises. Repair work on larger motors is
normally limited to replacement or refinishing of
bearings, commutators, collector rings, brushes, etc.
Motor rewinding should not be attempted by the
installation support groups (Directorate of Engineering and Housing, Public Works or Civil Engineer Shops) since it is more economical to contract
such work to commercial shops that specialize in
motor rewinding. With regard to the many thousands of fractional horsepower motors in operation
throughout the military services, it may be more
economical to replace a motor than to attempt to
repair it. The local electrical supervisor must make
this determination. Table 4-1 can be consulted to
aid in the selection of proper replacement motors.
Special consideration should also be given to highefficiency motors since they save both energy and
money throughout the life of the motor. The following safety precautions should be observed when
working on electric motors:
a. Make sure the machine is de-energized, tagged
and locked out before starting work (para 12–2).
b. Personal protective equipment such as
goggles, gloves, aprons and respirators should be
worn when working with hazardous substances
(chap 11).
c. Great care should be exercised in selecting solvents to be used for a particular task.
d. Adequate ventilation must be provided to
avoid fire, explosion, and health hazards where
cleaning solvents are used.
e. A metal nozzle used for spraying flammable
solvents should be bonded to the supply drum, and
to the equipment being sprayed.
f. After tests have been made, discharge stored
energy from windings by proper grounding before
handling test leads.
4-2. Alternating current (AC) motors.
AC motors should, with reasonable care, give long
continuous service. However, there is a tendency to
neglect motor maintenance and, as a result, motor
failures are frequent and repairs may become a
continuous and costly process. It is therefore recommended that a preventive maintenance program be
established to minimize emergency breakdowns.
The program should be supported with an effective
spare parts stock to speed up any unscheduled outages that may occur.
a. Squirrel-cage induction unit. This AC motor is
the most prevalent in use at military installations
(fig 4-l). The squirrel-cage motor is the most rugged and the least expensive of all types of induction
motors. The squirrel-cage motor is nearly a constant
speed machine. Typically its speed varies 0–5 percent from synchronous speed from no load to full
load. The basic design of the rotor can be modified to
provide a limited degree of external speed control.
b. Wound-rotor induction unit. This AC motor has
connected to its collector rings the insulated phase
windings on the rotor (fig 4-2). Through stationary
brushes in contact with the collector rings, any desired value of external resistance may be added to
the secondary (rotor) winding to give greater speed
control of the motor. Also, use of external resistance
allows the motor to deliver a high starting torque
with a relatively small inrush current.
c. Synchronous unit. This type of AC motor (fig
4–3) has an insulated winding in both the rotor and
the stator. A variable source of DC excitation is
supplied to the rotor winding and an AC line source
is supplied to the stator winding. A synchronous
motor is a constant speed machine with similar
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-1. Motor application guide.
TM 583/NAVFAC MO-116/AFJMAN 32-1083
Table 4-1. Motor application guide--continued.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-1. Motor application guide - continued.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4–1. Motor application guide - continued.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-1. Motor application guide - continued.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-1. Motor application guide - continued.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4–1. Cutaway view of squirrel-cage induction motor.
torque limitations. It may be used for power factor
improvement since a synchronous motor operates at
unity or a leading power factor (in addition to lagging power factor). They are also more efficient than
some induction or DC motors having the same
speed and power rating. But the higher cost, larger
size per horsepower and lower starting torque are
the disadvantages that limit synchronous unit application.
d. High-efficiency unit. This motor is specially designed to reduce electrical losses as much as 50
percent so that less electricity is used over the entire life of the motor. These motors also operate at
higher power factor values which help avoid power
factor penalties and reduce the cost of power factor
correction. They can deliver longer service, are more
reliable, and are more easily maintained than normal efficiency motors.
e. Components of AC machines. Maintenance op-
erations on an AC motor will encompass maintenance on the following components.
(1) Stator and rotor windings. The primary
parts of a typical motor are (fig 4–4): the frame and
base that support the assembled motor; the stator
which is the stationary part consisting of an iron
core and insulated windings; and the rotor which is
the rotating element. The term armature is often
used in lieu of rotor, particularly with DC motors
and for AC motors with commutators or collector
rings and brushes. Most stator and rotor problems
can be traced to winding failures. The life of a winding depends upon keeping it as near to its original
condition as long as possible. Insulation failure
causes immediate outage time. The following points
should be carefully examined and corrective action
taken during scheduled inspections to prevent operation failures.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4-2. Cutaway View of Wound-Rotor Induction Motor: a) Housing, b) Roto Assembly,
c) Slip Ring Brushes, d) Stator Windings, 3) Ball Bearings.
(a) Cleaning motor windings. Dust and dirt
are almost always present in windings that have
been in operation under average conditions. Dust
combined with high humidity becomes highly conductive. It may break down the winding insulation
and short circuit the motor windings. Frequent
cleaning and drying may be necessary. Removing
dry dirt with a clean, dry cloth is usually satisfactory if the apparatus is small and the surfaces to be
cleaned accessible. Do not use any material that
will leave lint, for lint will adhere to the insulation
and collect even more dirt. For removal of loose
dust, dirt and particles, vacuum cleaning is preferred rather than blowing out with compressed air
since there is less possibility of damage to the insulation and less chances of conductive or abrasive
particles getting into areas that may cause damage
during motor operation. Where dirt cannot be vacuumed, compressed air blowing may be used. However, care should be taken that the dirt is not blown
out of one machine into another. Air pressure should
not be greater than 30 psi. The air should be dry
and directed in such a manner as to avoid further
closing ventilation ducts and recesses in insulation.
Goggles or face shield should be worn when using
compressed air to clean motors. Accumulated dirt
containing oil or grease requires cleaning with a
solvent. The solvent should be as recommended by
the manufacturer. A rag, barely moistened (not wet)
with a nonflammable solvent, may be used for wiping. Avoid liquid solvent spraying which can carry
conductive contaminants into critical areas and contribute to short circuits and grounds. Apparatus
which has been clogged with mud from dust storms,
floods or other unusual conditions, will require a
thorough water washing. Usually, a hose at pressures not exceeding 25 psi is used. After cleaning,
the surface moisture should be removed immediately to keep the amount of water soaked up by the
insulation to a minimum. Silicone-treated windings
require special treatment, thus the manufacturer
should be contacted for advice.
(b) Drying motor windings. If after cleaning,
storing or shipping, tests indicate that the winding
insulation resistance is below a safe level (para
4-5), then the motor should be dried before being
placed in operation. Two general drying methods
commonly used are external or internal heat. External heat is preferred since it is the safer application.
When forced air is used (fig 4-5), it may be heated
electrically or by steam. This method is usually inefficient and costly unless built into the original
installation. Electrical space heaters or infrared
lamps may be used. They should be distributed so
as not to overheat the insulation. Coil insulation
may be dried by circulating current through the
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4-3. Cutaway view of synchronous motor.
Figure 4-4. Primary parts of an AC induction motor.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4-5 Cleaning and drying motors in place.
winding. However, there is some hazard since the
heat generated in the inner parts is not readily
dissipated. This method should be followed only under competent supervision. For synchronous motors, the “short circuit method” is sometimes used.
This method is achieved by shorting the armature
windings, driving the rotor and applying sufficient
field excitation to give somewhat less than full load
armature current. Once the drying process has been
completed, insulation testing of the motor winding
is recommended to determine whether the insulation has been properly reconditioned. If a motor
must continue to operate in a damp environment,
then special enclosures are necessary to limit the
effects of a moist atmosphere.
(c) Inspecting motor windings. Check winding tightness in the slots or on the pole pieces. One
condition which hastens winding failure is movement of the coils due to vibration during operation.
Check insulation surfaces for cracks, crazing, flaking, powdering, or other evidence of need to renew
insulation. Usually under these conditions, when
the winding is still tight in the slots, a coat or two of
air-drying varnish may restore the insulation to a
safe value. Check the winding mechanical supports
for insulation quality and tightness, the binding
ring on the stator windings, and the glass or wirewound bands on rotating windings. E x a m i n e
squirrel-cage rotors for excessive heating or discolored rotor bars which may indicate open circuits or
high resistance points between the end rings and
rotor bars. The symptoms of such conditions are
slowing down under load and reduced starting
torque. Repairs to cast aluminum rotors with open
bars are not feasible and such rotors have to be
replaced. Copper bar rotors can usually be repaired
by rebrazing the joints.
(2) Bearings. The bearings are the most critical
mechanical part of a motor. To assure maximum
life, bearings should be subjected to careful inspection at scheduled intervals. The frequency of inspection is best determined by a study of the particular
motor operating conditions. Bearings are subject to
metal fatigue and will eventually wear out even
though they are correctly applied, installed and
maintained. Fatigue failures are characterized by
flaking of the race surfaces along the ball or roller.
Fatigue is a gradual process, which is dependent
upon load and speed and usually is made apparent
in its early stages by an increase in the operating
temperature, vibration or noise level of the bearing.
Bearing failures not attributed to fatigue failure are
usually classified as premature. The majority of
these premature failures are caused by the following: incorrect bearing type; misalignment of the
motor or load; misalignment or improperly installed
bearing; rusting during storage; preloading or improper end-play adjustment; excessive thrust or radial force; axial indentations; improper lubrication
and entrance of contaminants into bearing. Follow
manufacturer’s instructions and use lubricants as
specified. When using greases, store in clean containers, handle with clean paddles or use a grease
gun and keep containers covered. Do not overfill
bearing housings. Overfilling contributes to heat
build-up, damaged seals, leaks and collecting of
dirt. Overheating is particularly true of bearings
running at high speeds. Machines that are normally
idle for long periods should be exercised on a scheduled basis. Exercising will keep the oil circulated,
reduce condensation within the housing and lessen
the chances of flat spots developing on the bearing
races, balls or rollers. Inspect seals and vents regularly. Periodic maintenance services of bearings involves keeping a bearing dry, covered, clean and
lubricated as well as checking operating temperature. A clean bearing is particularly critical because
dirt means damage. It is therefore important to
remember the following when cleaning bearings (fig
(a) Work with clean tools in clean surroundings. Do not use wooden mallets, dirty, chipped or
brittle tools, or work on rough or dirty bench tops.
(b) Remove all dirt from the housing before
exposing the bearings and take care to prevent loose
dirt from getting into the housing.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Bearing is opened
on a clean bench
and is not removed
from package until
ready to be installed.
should not be opened and exposed to
dirt before they are
ready to use.
Bearing should not
be forced on shaft
by means of the
rings. It
not be
forced on a badly
worn shaft, or a
shaft that is too
Bearing is proper
size for the shaft
and is being tapped
into place by
means of a metal
tube that fits against the inner
This new bearing
does not have to be
cleaned. The slushing oil on packed
bearings should
not be removed.
r -
New bearing is re.
moved from container and immediinstalled.
Packed bearings
are already cleaner
than you can make
Loose bearing covers permit dirt to
get into bearing,
causing excessive
wear and heating.
Protective covers
are tight to prevent dirt getting
into bearing.
Figure 4-6. Bearing installation precautions.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(c) Handle bearings with clean, dry hands in
conjunction with a clean, lint-free rag. This will
limit the chance of corrosion due to perspiration.
(d) Handle a reusable bearing as carefully as
a new one.
(e) Use approved solvents and oils for flushing and cleaning. Apply fire-preventive precautions
if the solvent or oil is flammable.
(f) Lay bearings out on clean paper. Keep
bearings wrapped in oil-proof paper when not in
(g) Protect disassembled bearings from dirt
and moisture.
(h) Do not spin uncleaned bearings. Rotate
them slowly while washing. A bearing should not be
judged good until inspected after cleaning.
(i) Do not spin any bearing with compressed
(j) Soak bearings thoroughly in plenty of solvent. Then rinse them in a separate clean container
of clean solvent. Once cleaned, inspect the bearing
surfaces for nicks or scratches;. broken or cracked
rings, separators, balls, or rollers; and discolored,
overheated bearings. If the bearing is to be reused
in a short time, dip it in rust preventive, wrap in
grease-proof paper and store. For longer storage,
coat all bearing surfaces with a light protective
grease, wrap in grease-proof paper and store.
(k) Clean the inside of the housing before
replacing bearings.
(l) Keep bearings in their original carton until ready for use if they are new. Do not wash the oil
or grease out of a new bearing. Do not disassemble
new bearings.
(m) Install bearings properly after cleaning.
(3) Ball and roller bearings. External inspection of ball and roller bearings (fig 4-7) at the time
of greasing will determine whether the bearings are
operating quietly and without undue heating.
Equipped with a grease chamber, they can be very
easily overgreased. Overgreasing may be prevented
by opening the grease relief plug (fig 4-8) after
greasing has been completed and running the motor. When excess grease has drained through the
relief plug, secure the plug.
Since ball bearings are often sealed, they require
little maintenance but it is very important that the
grease be kept clean. This also applies to sealed
housings (with the exception of permanently sealed
bearings) which should be cleaned and regreased
every 2 years or as recommended by the manufacturer. The bearing housings may be opened to check
the condition of the bearings and lubricant. If the
lubricant must be changed, the bearing and housing
parts should be thoroughly cleaned and new lubricant added. Special instructions regarding the type
or quantity of lubricant recommended by the manufacturer should be followed. In all cases, standard
lubricating practices should be followed.
(4) Sleeve bearings. Sleeve bearings (fig 4-9)
are most often used in fractional horsepower motors. For older types of sleeve bearings, the oil
should be drained, the bearing flushed, and new oil
added at least every year. Newer sealed type sleeve
bearings require very little attention since the oil
level is frequently the only check needed for years of
(5) Insulation. Failure of insulation is another
major factor in motor breakdowns. Few types of
insulation failures can be readily repaired. Insulation internal to the motor should be visually
checked and defects further investigated. Heat is
one of the principal causes of insulation failure in a
motor. Make sure that the motor has adequate ventilation and that air openings are not obstructed.
Also make sure that the motor is not overloaded
which increases operating temperatures. Most motors are equipped with thermal overload devices
applied directly to the motor winding which measure increases in temperature. At a predetermined
temperature, the overload device will trip and disconnect the motor from the circuit. When an overload device has tripped, the operator should determine the cause of overheating, correct it if possible,
and reset the overload before restarting the motor
(para 5-4e). An indication of the condition of the
insulation can be determined by performing an insulation resistance test (para 4-5).
4-3. Direct current (DC) motors.
On military installations, DC motors (fig 4-10) are
used only if AC voltage is not available or where
there is a wide range of speed control desired. The
reason for using a DC motor is often solely to
achieve speed control. DC motor speed can be varied
intentionally by varying the field current on shunt
wound motors or by varying the input voltage to
either series or shunt motors. DC motors are classified into different types based on the connection of
the various windings. Shunt and series are considered the two basic types of motors, as all others are
derivatives of the two.
a. Shunt motors. The most widely used type of
DC motor is the shunt wound motor. As the name
implies, these machines have the armature and
field circuits connected in parallel (shunt) to a constant source of voltage (fig 4-11a). While the term
“shunt” is still used, relatively few motors are now
applied in this way. Shunt motors as now applied
have their field circuits excited by a source of power
that is separate from the armature source of voltage. The field excitation voltage level is usually the
TM 5483/NAVFAC M-l 16/AFJMAN 32-1083
Straight Roller Bearing
Ball Bearing
Ball Thrust Bearing
t-~ — - B o R E - j 1
Tapered Roller Bearing
l - SE P A R A T O R
Needle Roller Bearing
S H E L L-
Figure 4-7. Construction of ball and roller bearings,
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
Figure 4-8. Greasing Bearings: a) Wipe away dirt from fitting or plug, b) Remove lower plug, C) Catch any run-out,
d) Add new grease, e) Run motor and allow excess grease to escape, f) Install and tighten lower plug.
same as the armature voltage, however, special field
voltage ratings of 15 to 600 volts are available for
application as a modification. The shunt motor is
characterized by its relatively small speed change
under changing load.
b. Series motors. As the term implies, series motors have their field windings connected in series
with the armature circuit, therefore, it carries full
motor current (fig 4-11b). Series connection results
in a characteristic whereby motor speed is a function of load. Thus, the series motor is a variable
speed motor.
c. Compound motors. A motor which is built with
both shunt and series fields is termed a compound
wound motor (fig 4–11c). By proportioning the relative amounts of series and shunt windings, the designer may shift the motor characteristics to be
more nearly shunt or more nearly series in nature.
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
Figure 4-9. Typical sleeve bearings.
Figure 4–10. Cutaway views of a typical DC motor
TM 5-683/NAVAC MO-116/AFJMAN 32-1083
] [ F2]
v s o u c e
[ A 2 ]
[ S 2 ]
[ A 2 ] [ S l ]
Figure 4–11. Main Types and Connections of DC Motors: a)
Shunt motor b) Series motor c) Compound motor
d. Components of DC machines. The basic operating and maintenance requirements for DC motors
are similar to those for AC motors. There are some
special requirements due to the peculiar construction features of the DC motor. The recommendations that follow, particularly those for the armature (fig 4–12), also apply to AC synchronous
motors, It is important that the armature be kept
clean. Dust, grease, corrosive gases, moisture and
oil are particularly harmful.
(1) Field windings. The field is made up of a
frame with field poles fastened to the frame’s inner
circumference. The field windings, mounted on
laminated steel poles, furnish excitation for the motor. Inspect field winding insulation and determine
if they are dirty and oil-soaked. Check for malfunctioning controls which cause excessive field current
that can cause excessive heating and failure. Other
causes of winding heating are excessive voltage, insufficient speed, off-neutral brushes, overloads and
partial short circuit in a field coil. Never run a DC
motor with the field circuit open. If the field winding is open-circuited, the motor will fail to start or
will operate at excessive speeds at light loads, and
excessive sparking will occur at the commutator.
Check the insulation resistance of the windings
(para 4-5).
(2) Brushes. Maintenance and inspection of
brushes should be performed regularly to ensure
the following (fig 4-13):
(a) Brushes are not loose in their holders.
Replace worn brushes. NOTE: Replacement
brushes are of several types and grades. Successful
motor operation depends upon proper selection of
the replacement brush best suited for the service
requirements of the motor.
(b) Brushes are not sticking in their holders.
Clean brushes and holder.
(c) The tools and/or heels of the brush face are
not chipped or cracked. Replace brush if damaged.
(d) Brush shunt leads are properly attached
to the brushes and their holders. Replace brush if
shunt lead is loose at the brush. Tighten if lead is
loose at the holder.
(e) Correct brush tension is maintained. Readjust the brush spring pressure in accordance with
the manufacturers’ instructions when adjustment is
provided. When adjustment is not provided, replace
the spring.
(f) Brush holder studs are not loose. Tighten,
if loose.
(g) Brushes are not discolored. Brushes
should have a highly glazed or very dull finish.
Clean the brushes when they become black or grey.
(h) Reset brushes at the correct angle.
(i) Reset brushes in the neutral plane.
(j) Properly space brushes on the commutator to 1/32 inch.
(k) Correctly stagger the brush holders.
(l) Properly space brush holders from the
commutator (usually l/16 to 3/16 inch.). If the
proper spacing is not maintained, the brushes will
ride the surface of the commutator poorly. This is
especially applicable to the motor using an inclined
brush holder since the brush will be shifted to the
neutral position, leading to poor commutation.
(m) Check to ensure that the correct grade of
brush, as recommended by the manufacturer, is being used.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4-12. Armature of a large DC motor on stands.
Figure 4-13. Inspecting and installing brushes on a large DC motor.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(3) Commutators. A cutaway section of a commutator is shown in figure 4-14. The primary
source of unsatisfactory commutation is due to
faulty operating conditions. Therefore, the principal
maintenance function is that of keeping the commutator surface clean, concentric, smooth, and properly undercut. Surfaces of the commutator bars
must be even and free of ridges so that the commutation is concentric, thus allowing any object held
against it to react as though it were held against a
smooth surface cylinder. Inspection and maintenance methods are as follows:
(a) Check for indication of brush chatter (fig
4-15). Brush chatter is most evident by chipped
brushes. This condition results from either a poor
commutator surface or high friction between the
brush and commutator. High friction is normally
caused by operating the motor under a light load,
operating the motor under a load that exceeds the
commutator’s rated capacity for prolonged periods
or, film build-up on the commutator. Remedies
are: increase the load; reduce the load; and, clean
the commutator respectively.
(b) Check for threading or streaking (fig
4-16). Threading or streaking of commutator surfaces is characterized by fine lines inscribed around
the commutator. It results when copper particles
transfer to the face of the brush. These particles cut
through the commutator film, creating areas which
carry more than their share of current. They also
cause rapid wearing of the brushes and lead to commutator resurfacing. Use of natural graphite
brushes, which have cleaning action, cuts down on
the formation of film that hinders passing current.
Maintenance personnel should check for any evidence of the lack of uniformity in brush action on
the commutator surface and film. Evidence of such
action should be corrected as soon as possible.
(c) Check for sparking. Sparking often results from poor commutation. This condition may be
improved by repositioning the brushes so that they
are slightly against rotation. When repositioning
the brushes that do not provide better commutation, the commutating-pole air gap must be adjusted.
(d) Check for flashing. Flashing normally results from conditions that cause a sudden change in
the field strength of the motor’s current or voltage.
Flashing can be prevented by frequent checks and
elimination of conditions that contribute to shortcircuiting.
Figure 4-14. Cutaway section of a commutator.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4-15. Brush "Chatter" Action.
(e) Check film on commutator for even and
uniform color (fig 4-17). The color should be between light to dark brown. Clean the commutator as
frequently as required to maintain the proper color.
(f) Copper pickup from the commutator surface, indicated when copper fragments become embedded in the brush faces, constitutes a danger signal and, unless corrected, becomes progressively
worse. The condition can be corrected by providing
proper bar-edge bevelling, sanding the brush faces,
and thoroughly blowing out the motor after all other
work has been completed.
(g) Check the commutator concentricity with
a dial gauge (fig 4-18). A dial reading of .001 inch on
high speed machines to several thousandths of an
inch on low speed machines can be considered normal. When evidence indicates that the commutator
is out of round or eccentric (fig 4-19), it can be
restored by grinding” with a grinding rig. While
grinding, vacuum frequently to prevent copper and
stone grindings from getting into the windings.
Grinding should be performed only by experienced
personnel when the proper tools are available.
(h) After grinding the commutator, the mica
insulation separating the copper segments must be
undercut (fig 4-20). Bevel the edges of the bar and
clean the commutator slots. Bevelling eliminates
the sharp edge under the brush at the entering side.
Again, follow the manufacturer’s instructions in
this repair function. Do not attempt this operation
unless proper tools, instruments, and qualified personnel are available.
(i) After conditioning a commutator, ensure
that it is clean of traces of copper, carbon, or other
4-4. Motor operating considerations.
Often problems that cause motor breakdown and
premature failure can be traced to inadequate consideration of operation and application of the motor.
To enhance motor operation and improve longevity
consider application, type of motor, horsepower,
speed, voltage rating and environmental conditions
(table 4-1). The following paragraphs reiterate the
major causes of motor failures.
a. Dirt. Dirt can: plug ventilating spaces, interfering with proper cooling; glaze the faces of commutator brushes, resulting in harmfiul sparking;
blanket windings, interfering with heat radiation
and causing dangerous temperature rises; build
into a hazard of shorting or grounding, if metallic
particles are present and, cause complete motor
b. Dust. In open-type motors, use every possible
means of keeping out dust. Under no condition
should dust be allowed to come in contact with the
bearings. Keep the oil-fill caps closed at all times;
maintain the dust seals and gaskets in good condition and replace them when worn. Keep plenty of
clean rags available for wiping off the motor housings, cleaning commutators and removing dust from
wound sections. Vacuum loose dirt within the motor.
If vacuum cleaning is not effective, blow out the
windings with dry compressed air at a pressure not
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4-16. Poor Commutator Conditions: a) “Threading”, b) “Streaking”.
.. .
to exceed 30 psi. Greater pressure may loosen the
insulation and blow dirt under it. If blowing or
vacuuming will not remove accumulated dirt, use
solvents as recommended by the motor manufacturer.
c. Moisture. Moisture soaks into and softens
winding insulation until it is no longer adequate as
an insulator. When moisture gets inside a motor, it
unites with dirt to form a sticky mass. This mass
absorbs acid fumes and alkali fumes present in the
air. These fumes quickly change the mass into an
active destructive agent and a conductor of leakage
currents. Moisture preventive measures are simple
and therefore will not be discussed in detail. However, close attention to good housekeeping methods
is necessary. Open-type motors should not be exposed to intrusion of water from drip or splatter.
Standby motors should be run for a short time at
least once a week to guard against moisture condensation during periods of idleness. Before using an
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4-18. Example of eccentric commutator.
Figure 4-17. Good Commutator Films: a) A light, mottled
surface, b) Heavy film of nearly uniform color.
air line to blow out motor windings, first check to be
sure that water has not condensed in the line.
d. Friction. Many motors fail because of excessive
friction. Oil in sleeve bearings adheres to the shaft
and is dragged along by rotation, forming a lubricating film that prevents friction. It is important to use
the right oil at the right time and not too much.
Follow the manufacturer’s instructions. Do not add
Figure 4-19. Dial gauge to measure commutator concentricity.
new oil while the motor is running since it is easy to
add too much. Check the oil while the motor is
stopped and, if required, add oil to the full level.
Excess oil is apt to leak into the motor and cause
damage such as:
(1) Deteriorate the mica-insulating segments
between commutator bars.
(2) Foul the commutator bars.
(3) Soak windings to the point where rewinding may be the only way to prevent burnout breakdown of the motor.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4-20. Common undercutting mistakes.
e. Installation. One of the most important
antifriction precautions for motors with ball or
roller bearings is to ascertain that the bearings are
properly installed. The inner race should be tight
enough on the shaft to rotate with it, but not so
tight as to cause frictional distortion. Ball or roller
bearings are normally lubricated with grease, and
as in the case of oil lubricants mentioned above,
apply grease in accordance with the manufacture's
f. Vibration. Excessive vibration can loosen various parts, break electrical connections, crystallize
portions of the metallic structure and contribute to
an increase in frictional wear. Checks should be
made regularly to identify conditions that contribute to vibration such as misalignment, settling of
the foundation, heavy floor loading, and excessive
bearing wear particularly when records indicate freequent motor failures. Check to determine whether
vibration in the driven machine is being transmitted to the motor. Check that the motor is properly
applied for a particular load. Check for excessive
belt or chain tension. The trouble may lie in the
push-apart effect inherent in spur gears. Check for
motor-shaft oscillation resulting from a loose bearing. Check for loose motor-mounting bolts.
g. Applied voltages. For general purpose applications, a range of five percent under to five percent
over the nameplate voltage may be applied with
satisfactory results. A motor with a nameplate rat-
ing of 230 volts will give reasonable performance
on: 220, 230 and 240-V systems. A motor with a
single voltage rating of 230V will probably overheat
if run on 208V. Most manufacturers recognize this
problem and build extra capacity into the windings
to give a dual or triple voltage rating on the nameplate, that is: 208/230/240 volts. There are some
cases where motors fail due to low voltage. If a
given motor is fully loaded or slightly overloaded, it
will operate within its temperature limits for normal voltages. For voltages 90 percent and less of the
nameplate rating, the same motor will severely
overheat. The motor will fail if the low voltage condition is applied for long periods of time. The important thing to remember is that, in the example
given above, a fully loaded motor must have 100
percent of its nameplate conditions in order to deliver 100 percent of its capacity. A motor that only
needs to deliver 80 percent of its nameplate horsepower rating will most likely survive a prolonged
low voltage condition resulting in a somewhat
higher than normal temperature. This is sometimes
referred to as "service factor". Motor performance
guarantee is based on its nameplate rating and not
the system nominal voltage. The relationship between the nominal and nameplate rating is shown
in table 4-2.
h. Choice. There is usually some choice in the
substitution of voltages for the motors and applications shown in table 4-2. It is not necessary to
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-2. Nameplate voltage ratings of standard induction motors.
Single-phase rotors
Three-phase motors
(a) From ANSI/IEEE Std. 141-1984
“special order” rewinding repairs or replacements
for general purpose work. There are some cases
where substitution cannot be used. An exact voltage
replacement should be ordered if:
(1) The motor is known to be delivering 100
percent or more, continuously.
(2) Motor has a duty rating other than “continuous” or “24 hours”.
(3) Motor is marked, “special purpose”, or “severe duty” on nameplate.
(4) A non-standard voltage is shown and no
horsepower rating is given.
4-5. Motor insulation testing.
The electrical test most often conducted to determine the quality of low voltage motor armature and
winding insulation is the insulation resistance test.
There are other tests available to determine the
quality of motor insulation, but they are not recommended for low voltage motor testing because they
are generally too complex or destructive. An insulation resistance test should be conducted on rotating
machinery immediately following their shutdown
when the windings are still hot and dry. A megohmmeter (para 13–4) is the recommended test equipment. It should be applied to armature and rotating
or stationary field windings. Before testing the motor insulation, de-energize the circuit. Then disconnect any potentially low insulation sources, such as
lightning arresters, capacitors and other voltage
sources. Lead-in cables or busses and line-side circuit breakers or starters can be tested as a part of
the circuit provided a satisfactory reading is obtained. Motor test connections for AC and DC motors are shown in figure 4-21. If the insulation
resistance is below the established minimum, the
circuit components should be tested separately to
isolate the source of low impedance. All data should
be recorded and compared to previous periodic readings. Any persistent downward trend is an indication of insulation trouble even though the values
may be higher than the recommended minimum
acceptance values which are:
AC and DC motor (250V or less) 500,000 OHMS
AC and DC motor (1OOOV or less) 1 MEGOHM
4-6. Motor trouble-shooting.
Tables 4-3, 4-4 and 4-5 provide detailed data on
troubleshooting motor breakdowns. Motor troubles
along with their probable cause(s) and recommended maintenance or corrective actions are also
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 4-21. Connections for Testing Motor Insulation Resistance: a) (Top) connections for a DC motor
b) (Bottom) connections for an AC motor.
TM 5-683/NAVFAC MO-1161AFJMAN 32-1083
Table 4-3. AC induction motor trouble-shooting.
Motor will not
Probable Cause
Overload Control Trip
Power not connected
to motor.
Try starting
Wait for overload to cool.
If motor still does not start,
check, all the causes as outlined below.
Connect power to control, check control
sequence and power to motor.
Check Connections.
Test fuses and circuit breakers.
Faulty (Open) fuses.
Low voltage.
Check motor-nameplate values with power
Also check voltage at motor
terminals with motor under load to be
wire size is adequate.
Check connecti o n s w i t h c o n t r o l w i r i n g
Wrong conrol
Loose Terminal- lead
Tighten Connections.
If rotor starts
Disconnect motor from load.
check driven machine.
Check for open circuits.
Driven machine
Check for shorted coil.
Open Circuit in
stator or rotor
windi ng.
Short circuit in
stator winding.
Test for grounded
Free bearings or replace.
Use special lubricant for special conditions
Winding grounded.
the control
Bearing Stiff.
Reduce Load
Grease too stiff.
Isolate and
discharge capacitor check
If opened or shorted, replace.
Faulty c o n t r o l .
Stop motor, than try to s t a r t .
start on single phase.
Failed s t a r t e r
Check for "openU
in one of the lines or
Check current balance.
Motor noisy.
Motor running single
Check aligmen t a n d c o n d i t i o n o f b e l t . O n
pedestal -mounted bearing, check cord play
and axial centering of rotor.
Electrical load
Shaft bumping
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-3. AC induction motor trouble-shooting-continued
. .
Motor vibrates.
At higher than
normal temperature
or smoking.
Probable Cause
Vibration from
unbalanced or
Balance or align machine.
Possible mechanical
system resonance.
If motor
Remove motor from load.
i s s t i l l n o i s y , rebalance motor.
Air gap not uniform.
Center the rotor and if necessary
replace bearings.
Noisy ball bearings.
Check lubricants.
bearings if noise is persistent
and excessive.
Loose punchings or
loose rotor on shaft.
Tighten all holdings bolts.
Rotor rubbing
Center the rotor and replace
bearings if necessary.
Objects caught
between fan and end
Disassemble motor end clean it.
Any rubbish around motor should be
Motor loose on
Tighten holding-down bolts.
may possibly have to be realigned.
Coupling loose.
Check coupling joint.
Tighten coupling.
Measure motor Loading with wattReduce toad.
Electrical Load
Check for voltage unbalance or
single phasing.
Fuse blown, faulty,
control, etc.
C h e c k f o r " o p e nU in one of the
lines or circuits.
Clean air passages and windings.
Incorrect Voltage and
values with
Check motor-nameptate
power supply.
Also check voltage
at motor terminals with motor
under full load.
Motor stalled by
driven machine or by
tight bearings.
Remove power from motor.
machine for cause of stalling.
Stator winding
Use insulation testing procedures.
Stator winding
Use insulation testing procedures.
Table 4-3. AC induction motor trouble-shooting-continued.
At higher than
normal temperature
or smoking (Cont'd)
Bearings Hot
Sleeve Bearings hot.
bearings hot.
Probable Cause
or replace
Rotor winding with
Loose connections.
if possible,
with another rotor.
Belt too tight.
Remove excessive pressure o n
Motor used for rapid
reversing service.
Replace with motor designed for
this service.
End shields loose or
not replaced
Make sure end shieds fit squarely
and are properly.
Excessive belt
tension or excessive
gear side thrust.
Reduce belt tension or gear
pressure end realign shafts. See
that thrust is nott being
transferred to motor bearing.
Bent shaft.
Straighten Shaft.
A d d oil - i f o i l s u p p l y i s v e r y
flush and refill.
low - drain,
Foreign material in
oil or poor grade of
D r a i n o i l , flush, and relubricate
using industrial lubricant
recommend by a reliable oil
Oil rings rotating
slowly or not
rotating at all.
Oil too heavy; drain and replace.
M o t o r titled too far.
Level motor or reduce
realign, if necessary.
Rings bent or
otherwise damaged in
Replace rings.
Ring out of slot (oil
ring retaining clip
out of place).
Adjust or replace retaining clip.
Defective bearings or
rough shaft.
Replace bearings.
Too much grease
R e m o v e relief plug and let motor
If excess grease doe not
come out, flush and relubricate.
Wrong grade of grease
Add proper grease
Oil ring has work spot; replace
with new ring.
Remove relief plug and regrease
Foreign material in
Flush bearings, relubricate;
sure that grease supply is clean.
(Keep covered when not in use).
Bearings misaligned
Align motor and check bearinghousing assembly.
See that races
are exactly 90 degrees with shaft.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-3. AC indution motor trouble-shooting-continued.
Ball bearings
(cont’d. )
Bearings damaged
(corrosion, etc. )
Replace bearings.
Coupling loose.
Check coupling joint.
Tighten coupling.
Wound rotor motor
Motor runs at low
speed with external
resistance cut out.
Excessive vibration
and noise.
Wires to
Use larger cable to c o n t r o l .
Control too far from
Bring control nearer m o t o r .
Open circuit in rotor
circuit (including
cable to control).
Test to find open circuit and
Brushes sparking.
Check for looseness, overload, or
Dirt between brush
and ring.
Clean rings and insulation
Brushes stuck in
Use right size b r u s h , c l e a n
Incorrect brush
Clean brush tension and correct.
Rough collector
Sand and polish.
Eccentric rings.
Turn in lathe or use portable tool
to true up rings without
disassembling motor.
Open rotor circuit.
Current density of
brushes too high
Reduce load.
(If brushes have
been replaced, make sure they are
of the same grade as originally
Ring threading
Low current density.
manufacturer for different brush
Faulty Connection.
I n s p e c t for open or poor
connect ion.
Open circuit one
connectons or
locate and r e p a i r .
Short circuit
Open and repair.
Voltage falls
Reduce the impedance of the
external circuit.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-3. AC induction motor trouble-shooting--continued.
Motor will
(cont ’d)
Probable Cause
Friction high
Make sure bearings are properly
Check bearing tightness.
Check belt tension.
Check load friction.
check alignment.
Field excited.
Be sure field-applying
is open and field-discharge
contractor is closed through
discharge resistance.
Load too great.
Remove part of load
Automatic field relay
not working.
contractor tips.
Wrong direction of
S u p p lY
to solenoid.
Reverse any two main leads of 3phase motor.
reverse starting
winding leads.
Motor will not come
up to speed.
Excessive load.
Decrease the load.
Check operation of unloading
device (if any) on driven machine.
Low voltage.
Field excited.
Be sure field-applying
is open, and field-discharge
contactor is closed through
discharge resistance.
No field exc itation.
Check circuit connections. Be
sure field applying contactor is
Check for open circuit in field or
Check exciter output.
Check rheostat.
Set rheostat to give rated field
current when field is applied.
Check contacts of s witches.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-3. AC induction motor trouble-shooting-continued.
Probable Cause
Fails to pull into
step (cont'd).
Reduce load
Load excessive
Check operation of loading
device (if any) on driven machine.
Motor pulls
out of
step or trips
Inertia of load
May be a misapplication
Exciter voltage low.
Increase excitation.
- consult
Examine exciter as shown in D. C.
Check field ammeter and
its shunt to be sure reading is
not higher than actual current.
Open circuit in field
and exciter circuit.
Locate and repair break.
Short circuit in
Check with low voltage and
polarity indicator a n d r e p a i r
Reversed field
Check with l O w voltage and
polarity indicator and reverse
incorrect leads.
Load fluctuates
See motor "hunts",
Excessive torque
Check driven machine for bad
or consult motor
Power fails.
Re-establish power circuit.
Line voltage too low.
Increase if possible.
Fluctuating load.
Correct excessive torque peak at
driven machine or consult rotor
If driven machine is a compressor
check valve operations.
Increase or decrease flywheel
Try decreasing or increasing motor
field current.
Stator overheats
spots .
Rotor not centered.
Realign and shim stator or
Open phase.
Check connections and correct.
Field overheats.
Loose connections;
internal connections.
Short circuit in a
field coil.
Replace or repair.
Excessive field
Reduce excitation until field
current is at nameplate value.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-3. AC induction motor trouble-shooting-continued.
Probable Cause
All parts
Reduce load or increase motor
Check friction and belt tension or
Over or under
field excitation.
Excessive rooms
Adjust excitation to nameplate
Check circuit and exciter.
See that nameplate voltage i s
Remove any obstruction and clear
out dirt.
Supply cooler air.
TM 5-683/NAFAC MO-116/AFJMAN 32-1083
Table 4-4. AC synchronous motor trouble-shooting.
Motor will not
Probable Cause
Faulty connection.
Inspect for open or poor
Open circuit one
Short Circuit one
open and repair.
Voltage falls too
Reduce the impedance of the
external circuit.
Make sure bearings are properly
locate and repair.
Check belt tension.
load friction.
Field excited.
Be sure field-applying
is open and field-discharge
contactor is closed through
discharge resistance.
Load too great.
Remove part of load.
Automatic field relay
not working.
Check power supply to solenoid.
Check contactor tips.
Wrong direction of
Reverse any two main leads of 3- phase motor.
reverse starting
winding leads.
Motor will not come
up to speed.
Excessive load.
Decrease the load.
Check operation of unloading
device (if any) on driven machine
Low voltage
Be sure field-applying
is open, and field-discharge
contactor is closed through
discharge resistance.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-4. AC synchronous motor trouble-shooting-continued.
Probable Cause
No field excitation.
C h e c k c i r c u i t c onnections. Be
contactor is
sure field-applying
Check for open circuit in field or
Check exciter output.
Check rheostat.
Set rheostat to give rated field
currant when field is applied.
Check contacts of switches.
Load excessive.
Reduce load
Check operation of reloading
device (if any) on driven machine.
Motor pulls out of
step or trips
Inertia of load excessive.
May be misapplication
Exciter voltage low.
Increase excitation.
Examine exciter
its shunt to be
not higher than
as shown in D. C.
field ammeter and
sure reading is
actual currant.
Open circuit in field
and exciter circuit
Locate and repair break.
Short circuit in
Check with low voltage and
polarity indicator and repair
Reversed field spool.
Check with low voltage and
polarity indicator and reverse
incorrect leads.
Load fluctuates
See motor "hunts" below.
Excessive torque
Check driven machine for bad
or consult motor
Power fails.
Re-establish power circuit.
Line voltage too low.
Increase if possible,
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-4 AC synchronous motor trouble-shooting-continued.
Probable Cause
Fluctuating load.
Motor "hunts”.
Correct excessive torque peak at
driven machines or consult motor
If driven machine is a c o m p r e s s o r
check value operations.
Increase or decrease flywheel
Try decreasing or increasing motor
field current.
Field overheats.
All parts overheat.
Rotor not centered.
Realign and shim stator or
Open phase.
Unbalanced currents.
Loose connections:
internal connec tions.
Short circuit in a
field coil.
Replace or repair.
Excessive field
Redutce excitation until
current is at nameplate value.
Reduce load or increase motor
C onnections
and correct.
Check friction end belt tension or
Over or under
field excitation.
Adjust excitation to nameplate
Check circuit and exciter.
See that nameplate voltage is
Improper ventilatiion.
Remove any obstruction and clean
Excessive room
Supply cooler air.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 4-5. DC motor or generator trouble-shooting.
Motor will not
Probable Cause
Open circuit in
Check control for open in starting
c i r c u i t , open contacts, fuse or
Low terminal voltage.
Check voltage with nameplate
Bearing frozen.
Reduce load or use larger motor.
shaft and replace
in bearings to
make sure that the oil has been
replaced after installing motor.
Disconnect motor from driven
machine, and turn rotor by hand to
see if trouble i s i n m o t o r .
Strip and reassemble motor; then
check part by part for proper
location and fit.
S t r a i g h t e n or replace bent or
spring shaft (machines under 5
springs, need
Brushes not down on
Held up by brush
Brushes worn out.
Replace brushes.
Brushes stuck in
Remove and sand,
Power may be off.
Check line connectons to starter
with light.
clean up brush
Check contacts in starter.
Motor starts, then
stops and reverses
direction of
Reverse polarity of
generator that
supplies power.
Check generating unit
changing polarity.
Shunt and series
fields are bucking
each other.
Reconnect either the shunt or
series field in order to correct
the polarity.
Then connect
armature leads for desired
The fields
direction of rotation.
can be tried separately to
determine the direction of
connected so that both give same
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
5-1. Functions of motor controls.
The terms, controls, controllers, and starters are
used interchangeably. The most common name for
the device that controls the operation of the motor is
starter. This name is not the best description of the
device as the starter does much more than start the
motor. It also stops the motor, it provides overload
and short circuit protection, and it disconnects the
motor from the line after a period of overcurrent. It
may also contain auxiliary devices that limit the
motor inrush current, torque, and/or speed. Additional protection features may include undervoltage, phase reversal, and/or field loss.
5-2. Types of motor controls.
Some of the more common motor starters are described in this chapter beginning with the elementary document starter and ending with the more
complex adjustable speed frequency starter.
a. Document across-the-line starters. Document
starters are most often used on small single phase
fractional horsepower motors. They usually consist
of a push button-type or a toggle-type mechanism
(fig 5-1) that actuates a set of quick-make/quickbreak contacts that connect the motor directly to
the line. Document starters have provisions for
overload protection and their low cost provides economical starter selection for applications where no
undervoltage protection is required.
b. Magnetic across-the-line starters. Magnetic
starters are suitable for application over a wide
range of horsepower and voltage for both single and
three phase motors. Magnetic starters are full voltage starters designed to provide thermal overload
and undervoltage protection for squirrel cage motors and can be operated remotely from push button
stations or automatically, for example, through a
float switch. They differ from document starters in
that they contain a contactor which, when its electromagnetic coil is energized, closes its line contacts
to connect the motor directly to the line (fig 5-2).
The primary purpose of a motor starter is to provide
thermal overload protection, it is not designed to
interrupt fault current. A short circuit study must
always be performed to determine if protection is
necessary from fault currents and, if so, short circuit protection must be provided. A circuit breaker,
or fuses, upline of the contactor gives fault current
protection to the starter and the motor. Starters
must always include thermal overload relays. Ex-
ceptions are noted in NEC 430. Starters without
overloads are called contractors. The holding coil of a
magnetic starter (or contactor) is designed to drop
out whenever line voltage drops below about 60
percent of its normal value, thereby providing
undervoltage protection to the motor or load.
c. Combination starters. All motors, motor circuits and controllers require short-circuit and
ground-fault protection. This may be located with
the starter as in a combination starter or may be
the branch-circuit short-circuit and ground-fault
protective device as in a manual motor starter.
(NEC 430, part D). Starters connected to a power
distribution system with an available fault current
in excess of the starter short circuit interrupting
capacity must be protected from that fault current.
Combining a contactor with a thermal overload relay is called a magnetic motor starter and combining a magnetic motor starter with a circuit breaker
or fuses in a common enclosure is called a combination starter. These starters carry an interrupting
rating that indicates the ability of all components in
the integrated combination starter to withstand momentary overcurrent and thermal effects. Depending upon the type of short-circuit protective device
employed, combination starters (fig 5-3) may be
classified as breaker-protected starters, fuseprotected starters or fused breaker-protected starters.
(1) Breaker-protected starters. B r e a k e r protected starters use almost exclusively moldedcase breakers. Low voltage power circuit breakers
have sometimes been applied, especially for use on
larger motors- Breakers, as compared to fuses, are
slower in fault clearing for higher magnitudes of
short circuit currents. Consequently, three pole
breakers afford the least protection against thermal
overload relay and contactor damage. However,
they offer positive protection against single phasing. Breakers are usually designed for both thermal
and magnetic protection even though the overloads
are the best thermal protection because overload
relay heaters can be very closely selected to cause
tripping at precise values of current flow. Motor
circuit protectors (MCPs) used in combination starters are magnetic trip only and have no thermal trip
(2) Fuse-protected starters. Fuse-protected
starters provide the best degree of starter and thermal overload relay protection particularly for severe
short circuits (fig 5-4). The disadvantages of fused5-1
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 5-1. Manual starters
Figure 5-2. Typical magnetic starter
combination starters are possible single-phasing
and incorrect replacement of fuses.
(3) Fused breaker-protected starters. Fused
breaker-protected starters use a specific currentlimiting fuse to back up a breaker of specified type
and make to obtain a higher interrupting rating for
the combination while maintaining the advantages
of three-phase interrupters.
d. Reduced voltage starters. Reduced voltage
starters provide power to motors at lower starting
voltages resulting in reduced inrush currents and
reduced starting torques. Several types of starters
are discussed below.
(1) Autotransformer starters. These starters
generally insert autotransformers or reactors in series with the motor windings to limit starting cur-
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083/
Table 15-3. Interior wiring and lighting system.
Maintenance Group
Each scheduled
building visit
Unauthorized or nonstandard attachments
Defective convenience outlets and switches.
Improper cords.
Proper fuse sizes in panels.
Overheating of panels.
Any condition likely to cause fire. Check batterytype emergency lights and replacement lamps.
Check for Iamps larger than standard prescribed
for outlet.
A S Required
Replace burnt out lamps in hard-to-reach places.
(To be accomplished by electrical shop if special
equipment such as ladder trucks are needed).
Panels for circuit idenificaton and accessibility.
Replace blown fuses.
Replace burnt out or defective incandescent lamps.
Replace burnt out fluorescent lamps if personnel
have been instructed in this function and if assigned
to user. Promptly replace or report defective
lamps since a lamp approaching bum out flashes on
and off, causing overduty on auxiliary equipment.
As required.
Make repairs and adjustments to systems when
malfunctions are reported. Ensure that all work
complies with the NEC
As required.
Check ground resistance for special weapons
facilities at request of user.
Check for low voltages and/or low power factor.
Monthly or
Inspect station (substation switchgear or UPS) as
(1) Check electrolyte level and add distilled water if
(2) Check charging rate. Adjust charging rate as
necessary to maintain proper specific gravity.
(3) Test for proper operation under simulated
power interruption. Check maintenance free
batteries. Check voltage, check and clean
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 5-4. Coordination of motor overload relay and current limiting fuse.
rents. At military installations, they typically range
in size from 5 to 200HP, and the voltage may vary
from about 208V tQ 2300V. The autotransformer
starter provides greater starting torque per ampere
of starting current drawn from the line than any
other reduced voltage motor starter. Two contractors
are usually u s e d f o r c o n n e c t i o n o f a n
autotransformer starter. See figure 5-5. When the
start push button is pressed, start contactor “S”
closes. This contactor serves to connect the autotransformer to the line, and the motor to taps on the
autotransformer. After a defined timely delay governed by pneumatic timer TR, contactor “S” drops
out, and run contactor “R” closes, connecting the
motor directly across the line. At this time, the
autotransformer is disconnected from both the line
and the motor. It is important that contactor "S" is
dropped out before contactor “R” closes since any
overlapping of “R” and “S” in the closed position will
result in a short circuited autotransformer secondary. This would cause high current to flow and subject that winding to high thermal and magnetic
stresses. Standard autotransformers are equipped
with taps which allow them to be adjusted to operate at different percents of line voltage. Small sizes
are normally equipped with taps for 65 and 80 percent of line voltage, while larger sizes normally
have 50, 65, and 80 percent taps.
(2) Resistance starters. This starter limits the
starting current by employing resistors in series
with the motor windings. This provides a smooth
start and precise acceleration through a closed transition to full voltage and avoids a sudden mechanical shock to the driven load. Power and control
circuits of a resistance motor starter are given in
figure 5-6. When the start button is pressed, start
contactor “S” connects the motor to the line with the
starting resistor in series and a pneumatic timer is
also picked up. After a time delay governed by timer
TR, the TR/TC contacts close, Run contactor “R”
closes, short-circuits the starting resistor, and connects the motor across the line.
(3) part-winding starters. These are used with
squirrel cage motors having two separate, parallel
stator windings (fig 5-7). The motor is started on
one winding through accelerating contactor “lM” at
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Start Contactor
Run Contactor
Pneumatic Timer
Overload Relay
Contact Stays-Closed When TR Picks Up;
It Opens After A Time Delay.
Contact Stays Open When TR Picks Up;
It Closes After A Time Delay.
Figure 5-5 Autotransformer starter.
about 2/3 of normal inrush current. After a period of
acceleration governed by pneumatic timer-TR, the
other winding is energized through run contactor
‘2M”. This operation permits the use of contactors
which are half as large as those required for the
reduced-voltage starters, resulting in approximately a 50 percent reduction in cost. However, the
motor cannot carry its load until both windings are
(4) Wye-delta starters. A variation on the partwinding starter is the wye-delta type, which starts
the motor with the windings connected wye, and
after a period of acceleration, reconnects the wind-
ings for normal delta operation. This type is limited
to-wye-delta comectable motors but produces better
starting torque at a lower inrush current and is
used extensively with air-conditioning motors having a high inertia load and a long acceleration time.
(5) Solid-state starters. Solid-state starters (fig
5-8) provide smooth, stepless acceleration of squirrel cage motors from standstill to fill speed. It provides extended starting times by supplying continuously varying voltage to the AC motor from zero to
full voltage. Controlled starting of a standard squirrel cage motor is accomplished by supplying reduced voltage to the motor terminals. This reduced
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
cussed. Specialized guidance is required to install
and maintain this equipment. Consequently, the
manufacturer’s diagrams and instructions should
be obtained and kept readily available.
g. Adjustable speed/frequency starters. AC adjustable speed operation is obtained by converting
the fixed frequency AC line power into an adjustable voltage and frequency output which operates
the AC motor at the desired speed. The input AC
power is converted to adjustable DC voltage by a
solid-state converter module. The DC power is then
converted by the inverter to produce AC output
power at an adjustable frequency and voltage suitable for operating either conventional AC induction
motors or synchronous motors. Since the speed of an
AC motor is a function of the applied frequency,
accurate speed control is readily provided. These
systems are complex and may induce harmonics on
the electrical system which may, in turn, disrupt the
operation of nearby equipment. Maintenance
should be performed by personnel experienced with
solid-state drives and controls.
h. Miscellaneous types. Other terms used to de-
scribe motor controls include the following:
(1) Reversing starter. A motor that can be operated in either a clockwise or counterclockwise direction.
(2) Motor control center is the term given to a
grouping of motor starters within a large enclosure
(fig 5-9). The centers are used where several motors
are to be operated from a single location. The starters themselves may be magnetic across-the-line
starters or other types. A typical use would be in a
boiler control room where the various fan, pump,
conveyer, and other motors serving the boiler are all
controlled from a central location.
Figure 5-6. Resistance starter.
voltage produces reduced torque which means a
slow, controlled acceleration. Typical applications
that require lower controlled starting torques are
large pumps, compressors, and heavy material handling conveyors.
e. Two-speed starters. This circuit allows a motor
to be started at low speed before running it at high
speed. Resistors might be utilized to provide a
reduced-voltage start or a separate, lower line voltage may be available for low speed operation.
f. Starters and speed regulators for AC wound
rotor and DC motors. This equipment is much more
complex than the starting devices previously dis-
5-3. Components and maintenance of motor
Control equipment should be inspected and serviced
simultaneously with the motors. As a general rule,
overhaul procedures for control equipment are less
involved than motor overhauling. Most repairs can
be made on-site. Motor starters represent one area
in which simplicity of construction and wiring has
been emphasized by the manufacturers. Improvements have resulted in starters that are simple to
install, maintain and operate. Connections are
readily accessible, some parts are of plug-in type
and may be easily replaced. Coils are often encapsulated in epoxy compounds and are less likely to
burn out. Practically all newer starters have provisions for adding several auxiliary contacts with very
little effort. Spare parts for starters are usually
available from local suppliers. Spare starters, as
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
sizes should be stocked in the regular shop supply
a. Enclosures. Enclosures do not normally require maintenance when employed in a clean, dry
and noncorrosive atmosphere. But in a marginal
atmosphere, enclosures should be inspected and
maintained as recommended in paragraph 2-2. The
frequency of these inspections should be dictated by
the corrosiveness of the atmosphere.
b. Electrical connections. Experience indicates
that failures of electrical connections are the cause
of many equipment burnouts and fires. Refer to
paragraph 2–3 for recommended maintenance.
c. Molded case breakers. A wide variety of circuit
breakers are used in the military services. Thermalmagnetic molded case circuit breakers (fig 5-10) are
predominant in building panel boards and motor
control centers. They are available in bolt-in or
plug-in types and in single-pole for two-wire
three-wire ungrounded or three and four-wire
grounded circuits. Multiple units should be of the
common trip type having a single operating handle.
The need for maintenance on molded case breakers
will vary depending on operating conditions.
Molded case breakers are relatively trouble-free devices requiring little maintenance. For the most
part, maintenance will require only that conductor
terminations are tight and free from corrosion, and
that the breaker is kept dry and free from excessive
accumulations of dirt and dust. Because most
breakers employ welded internal construction, they
require no internal servicing. An exception to this is
the trip unit, which is replaceable on breakers in
larger frame sizes. Periodic inspection should be
made to ensure that the trip unit hold-down bolts
are tight. For breakers rated 100 amps and below,
and where inspection indicates some type of repair
is in order, "repair by replacement” is advisable.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 5-8. Solid-state starter
Small breakers are fairly low in cost, and labor costs
do not justify repair. For larger sizes, replacement
parts will include such items as handles, arc chutes,
and trip units. Trip units are sealed to prevent tampering. Where a trip unit itself is found to be faulty,
it should be replaced as a unit, rather than repaired. Some users maintain a regular program of
calibration checks (verification testing) to verify the
trip point. These tests can be performed on the
plant premises. In conducting such tests, care
should be taken to follow the manufacturer’s specific instructions. Where conditions are not closely
controlled, misleading results can be obtained. Test
limits provided by the manufacturer must be observed. But, generally, it is advisable to operate and
inspect the circuit breaker when maintenance of
other components of the motor controls or panel
board is being performed. Recommended procedures are routine testing and verification testing.
These two types of testing are optional and are
implemented at selected locations depending upon
the operating environment or critical load being
(1) Routine field testing. The following constitutes a guide for the types of tests which might be
performed during routine maintenance of moldedcase breakers. The tests recommended are based on
proven standard maintenance practices and are
aimed at assuring that the breaker is functionally
operable. All tests are to be made only on breakers
and equipment that are de-energized. Extreme atmospheres and conditions may reduce the dielectric
strength of any insulating material including those
of which molded case breakers are made. Therefore,
the first routine check recommended is an insulation resistance test (para 14-2). The voltage recommended for this test should be at least 50 percent
greater than the breaker rating. However, a minimum of 500 volts is permissible. Tests should be
made between phases of opposite poles as well as
from current-carrying parts of the circuit breaker to
ground. Also, a test should be made between the
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 5-9. Typical motor control center.
line and load terminals with the breaker in the open
position. Resistance values below one megohm per
kV of test voltage are considered unsafe and should
be investigated for possible contamination on the
surfaces of the molded case of the circuit breaker.
Clean the molded case surface and retest. If low
megohm readings persist, then replace the breaker.
For individual breaker resistance readings, load
and line conductors should be disconnected from the
breaker under test. If not disconnected, the test
measurements will also show resistance of the attached circuit. During routine testing, all circuit
breakers should be operated (while documenting)
several times to ensure that the contacts are not
frozen and that the mechanical components function without undue friction. This action will also
lessen the effect of any film that might have built up
on the contacts. Check for cracked, warped or broken case and replace if necessary. If there is evi-
dence of internal heating, or reason to suspect high
contact resistance or improper calibration, the
breakers should be replaced. It is recommended
that molded-case breakers with removable covers be
checked for contact and latch cleanliness as well as
connection tightness. Lubrication should be
checked. If the operating mechanism appears dry,
apply a drop of heavy oil or light grease at the wear
points. Do not apply lubricant to the contacts or to
the trip unit. If the contacts are badly pitted, they
should be cleaned with a fine file or sandpaper. Be
sure to avoid any accumulation of filings in the
breaker. Do not tamper with factory sealed breakers.
(2) Verification field testing. Verification field
testing of molded case circuit breakers is intended
to check breaker operation versus manufacturer’s
published data. If molded case circuit breaker performance characteristics are to be tested in the
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Molded Case —
-Arc Chute
-Movable Contact
Trip Indication
Trip Free
Trip Bar
Figure 5–10. Cutaway view of typical molded case circuit breaker.
field, there are many variables that must be recognized and taken into account. Underwriters Laboratories, Inc. (UL) “Standard for Branch Circuit and
Service Circuit Breakers” (#489) is the basis for
performance standards for all molded case circuit
breakers bearing the UL label. Anyone testing
molded case circuit breaker performance characteristics should study these standards and be familiar
with the conditions specified for the qualifying
tests. The principal purpose of field testing is not to
determine if the breakers exactly meet the manufacturer’s published curves but rather to determine
if the device is furnishing the protection for which it
was installed; namely, the protection of that part of
the electrical system to which it is applied. For
instance, a circuit breaker that trips in less than the
minimum time shown by the manufacturer’s trip
time curve may furnish more protection than expected. When field testing circuit breakers, it is
recommended that the overcurrent trip test be performed at 300 percent of rated current. The reaction
of the circuit breaker to this overload is indicative of
its reaction throughout its entire overcurrent trip
range. The 300 percent load is chosen as the test
point because it is relatively easy to generate the
required current in the field. Also, the wattage per
pole from line to load is small enough so the dissipation of heat in the non-active pole spaces is minor
and does not appreciably affect the testing results.
Various test equipment and test procedures are
available for molded-case circuit breaker testing (refer to the circuit breaker manufacturer for recommended testing equipment and procedures). Test
equipment generate high currents at low voltages
and are safe and convenient to use for field testing.
For specific minimum and maximum tripping times
given 300 percent current flow, refer to the manufacturer’s document for the breaker being tested (fig
5–11). If the breaker does not trip within the specified bandwidth, then the breaker should be replaced. The instantaneous magnetic trip characteristics of the breaker can be influenced by stray
Temp 0 25 40 50 60c
\ \
/ /
TM 5-683/NAVFAC MO-116/AFJMAN 32-10 83
Shift rods e.
for long-time
Figure 5-11. Molded case circuit breaker time-current curve.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
magnetic fields. The test setup must be conducted
in such a way that magnetic fields created by the
test equipment, steel enclosures, or the conductors
from the test equipment to the circuit breaker do
not affect the test results.
d. Fuses. Fuses are among the oldest types of
overcurrent protectors. They are simple, rugged and
inexpensive. They sense overcurrent conditions
through the development of heat in the conducting
elements and accomplish their operation by destruction of these elements. They offer both longtime and short-time short circuit protection and are
used widely in the protection of small motors. Maintenance of fuses should not be performed until all
power sources are disconnected (fig 5-12). At that
time, check the continuity of all fuses with an ohmmeter. A reading greater than zero ohms indicates
that the fuse is blown and must be replaced. Inspect
fuse terminals and fuse holder clips. Check that the
portions of the fuse making contact in the clip are
clean and bright; poor contact can cause overheating which results in a discoloration of the contact
surfaces. If this occurs, then the oxidized surfaces
should be cleaned and polished. Silver-plated surfaces should not be cleaned with an abrasive material. Wiping contacts with a noncorrosive cleaning
agent is recommended. Tighten all fuse holder connections. Fuse clips should exert sufficient pressure
to maintain good contact, which is essential for
proper fuse performance. Clips which make poor
contact should be replaced. Clip clamps are recom. .
when unsatisfactory clips cannot be re-
placed. Replace fuses showing signs of deterioration
such as discolored or damaged casings or pitted
contact surfaces. There are many types of fuses (fig
5-13) with various characteristics, some of which
are physically interchangeable. Make certain that
fuses are of the proper type and rating. Never replace one type of fuse arbitrarily with another type
fuse of the same physical size simply because it fits
the fuse holder. A continuity check should also be
performed on replacement fuses to ensure their integrity. Fuses should have correct current and voltage ratings, proper time-delay or current-limiting
characteristics and an adequate interrupting rating
to protect the circuit and its components Current
ratings of fuses protecting transformers or motors
should be selected at or near the fill load current.
Voltage ratings of fuses should equal or exceed their
circuit voltage. Interrupting ratings of fuses should
equal or exceed the available fault current at the
fuse holder. UL listed fuses without marked interrupting ratings are satisfactory only on circuits
where fault currents do not exceed 10,000 amperes.
Non-current-limiting fuses should not be used to
replace current-limiting fuses since fuse holders for
UL listed current-limiting fuses are designed to reject fuses which are not current limiting. Fuse holders and rejection clips should never be altered or
forced to accept fuses which do not readily fit. An
adequate supply of spare fuses, especially those
which are uncommon, will minimize improper replacement.
Figure 5-12. Fuse maintenance practices.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
0-600 v.
0-600 AMPS.
100,000 OR 2OO,OOO/AC
601-6000 AMPS
100,000 OR 200,00/AC
Figure 5-13. Underwriters’ Laboratories cartridge fuse classification.
e. Thermal overloads. Thermal overload relays
contained in starters provide more precise motor
protection against overloads and momentary surges
than fuses or circuit breakers. However, they do not
provide short circuit protection. Relays themselves
require little maintenance other than occasional
testing to ensure that they are operational. Thermal
overloads should be checked and resized whenever
the motor is replaced to adequately protect the motor. The relays are controlled by heater elements (fig
5-14) which are in series with the motor current.
The size of the heater must match the motor being
protected. Be especially careful if the motor has
been oversized to compensate for lower load current
with lower rated heaters to cause tripping on loss of
one phase (single phasing). It often happens that
the wrong size heaters are installed. If the heater is
too small, the overload relays act to take the motor
off line unnecessarily. If too large, the motor will
operate without proper protection and could be
damaged from overload. If the relays frequently operate to take the motor off line, the heaters should
be checked first. If the heaters are properly sized
(about 120 percent of motor full load current) and
there are no unusual temperature conditions, then
check the motor current. If the motor current is
higher than the nameplate rating by a margin sufficient to exceed the heater rating, then the relay is
operating properly, and the motor is either overloaded or in fault, therefore, check the motor. Do not
put in larger heaters. If however, the motor stops
frequently even though the heaters are correctly
sized and the line current and ambient temperature
are normal, then check the relays. The relays
should be tested and replaced if required. Unfortunately, the overload relays that serve as safety
valves to protect the motors from burnouts due to
faults and overloads, sometimes fail to respond
properly. For example, aging and inactivity followed
by metal fatigue in some relay types may result in a
failure to operate under conditions of overload. Periodic testing of the relays under load conditions,
checking the tightness of all overload connections
and inspecting for contact overheating and cleanliness forms an important part of a good motor control maintenance program. Suitable test instruments are available that provide a dummy load to
the relay and measure the time interval required to
open the contacts. Their use is highly recommended, especially on relays for motors that serve
critical loads; e.g., motors driving air conditioners
which are used for communication or data processing equipment, or motors on production lines. For
most applications, testing of motor overload relays
should be conducted every 2 years. Regular testing
of thermal overload motor relays is a recommended
procedure for all installations. Overload relays employ a thermal element designed to interpret an
overheating condition in the motor winding by converting the current in the motor leads to heat in the
overload relay element. As the heat in the element
approaches a predetemnined value, the control circuit to the magnetic contactor holding coil is interrupted and the motor branch circuit is opened. The
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 5-14. Typical terminal overload.
controller and motor should be located in the same
ambient temperature environment so that the overload relay can act accurately. If the controller is
located in a lower ambient temperature environment than the motor, it may not trip in time to
protect the motor. Vice versa, if the controller is in a
higher ambient temperature than the motor, it will
trip even if the motor is not in overload. The significant different ambient temperatures of the motor
and controller can be compensated by selection of a
relay heater or use of a relay that compensates for
temperature. The adjustments are to decrease the
motor current protection (lower trip setting) by one
percent for each degree Celsius the motor ambient
exceeds the controller normal ambient temperature
or increase the motor current protection (raise trip
setting) by one percent for each degree Celsius the
controller ambient exceeds the motor ambient. The
manufacturer’s published heater selection tables
should be referenced (fig 5-15). It should be noted
that in this case, according to the National Electrical Code, a disconnecting means must be located in
sight from the controller location.
f. Contractors. The part of the starter that contains the coil and contacts is known as the contactor
(fig 5-16). It is used to control the circuits to the
motor. Contractors are intended for repetitive operation, perhaps as many as a million or more operations. Normal wear and tear can be expected, and
therefore periodic inspections should be made to
ensure that all moving parts are functioning. properly.
(1) Copper contacts. Copper contacts should be
replaced when worn thin or badly burned and pitted. Both the moving and the stationary contacts
should be replaced to avoid possible misalignment
of an old contact with a new one. Check the contact
spring pressure with a scale in accordance with the
manufacturer’s recommendations. Adjust or replace
the springs as necessary to maintain good pressure
between pairs of contacts. When copper contacts
become excessively rough, they should be smoothed
with a burnishing tool or a fine file designed for this
purpose. Do not use emery cloth. Also, any copper
oxide on the contact surfaces should be removed.
Copper oxide is not sufficiently conductive, it acts as
a high resistance and could eventually cause overheating. When filing, particular care should be
taken to maintain the original shape of the contacts.
It is not necessary to develop smooth contact surfaces. In fact, better operation is obtained when the
surfaces are rough dressed. Contacts should not be
(2) Silver contacts. Silver contacts should not
be filed. Silver oxide, that forms on the contact surfaces, does not have to be removed because it is a
good conductor. Routine inspection should always
include checks for tightness of terminal and cable
connections as well as for signs of overheating. Replacements should be made as conditions dictate.
Manufacturer’s recommendations should be followed closely for maintenance and replacement of
(3) Shunts. Shunts are flexible bands of woven
copper strands carrying current from the moving
contacts to a stationary stud. If the shunt is unduly
bent or strands are broken, then it should be replaced.
(4) Coils. Coils require very little maintenance.
In fact it is generally more economical to replace the
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 5-15. Typical heater selection table for thermal overload device.
coil than it is to attempt repairs. Coils will operate
efficiently at 85 to 110 percent of rated voltage.
Higher voltages shorten life and lower voltages may
result in failure to close the contacts completely.
This could result in welded contacts. Coil burnout
also could occur if the contactor fails to close properly either from being blocked or by low voltage. In
either case, the current flowing through the coil is
larger than rated because of the larger air gap in
the magnetic circuit. Maintenance consists of cleaning out accumulated dust and grease, if any, and
inspecting the coil to see that it is of proper rating
and operates properly. When handling coils, do not
pick the coil up by its leads. If coils become wet,
they should be dried out by spraying a contact
cleaning chemical on the coil or by heating the coil
in an oven at 110 degrees C to 125 degrees C. If it is
necessary to varnish coils, use only an approved
insulating treatment applied while the coils are still
warm from baking. These instructions on drying
and varnishing coils do not apply to the newer encapsulated types.
5-4. Preventive maintenance and troubleshooting guide.
Table 5-1 outlines typical preventive maintenance
for a motor control. Table 5-2 lists troubleshooting
and corrective maintenance practices.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 5-16. A NEMA size 6 magnetic contactor (Courtesy of Siemens-Allis).
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 5-1. Motor control preventive maintenance guide.
Exterior and Surroundings
Interior of Enclosure,
Nuts and Bolts
Dust, grease, oil; high
temperature; rust and
corrosion; mechanical damage;
condition of gaskets, if any.
Same as for No. 1 plus excess
vibration which may have
loosened nuts, bolts or other
mechanical connections.
Contactors, Relays,
Contact Tips
Check control circuit voltage;
inspect for excess heating of
parts evidenced by
discoloration of metal,
charred insulation or odor;
freedom of moving parts; dust,
grease, and corrosion; loose
Check for excessive pitting,
roughness, copper oxide; do
not file silver contacts.
Check contact pressure; is
pressure same on all tips.
Flexible leads
Look for frayed or broken
strands; be sure lead is
flexible - not brittle.
Arc Chutes
Check for breaks or burning.
Check for freedom of movement;
do not oil.
Look for overheating, charred
insulation or mechanical
Clean faces; check shading
coil; inspect for
misalignment, bonding.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 5-1. Motor control preventive maintenance guide continued.
Fuses and Fuse Clips
Check for proper rating, snug
fit; if copper, polish
ferrules; check fuse clip
Overload Relays
Check for proper heater size;
trip by hand; check heater
coil and connection; inspect
for dirt, corrosion.
Pushbutton Station and
Pilot Devices
Check contacts, inspect for
grease and corrosion.
Dashpot-Type Timers and
Overload Relays
Check for freedom of movement;
check oil level.
Check for signs of
overheating; loose
connections; tighten sliders.
Tighten main line and control
conductor connection; look
for discoloration of currentcarrying parts.
Control Operation
Check sequence of operation of
control relays; check relay
contacts for sparking on
operation; check contacts for
flash when closing; if so,
adjust to eliminate contact
bounce; check light switches,
pressure switches, temperature
switches, etc.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 5-2. Motor control troubleshooting chart.
1. Contactor or Relay Does
not Close
No supply voltage.
Check fuses and disconnect
Low voltage.
Check power supplY.
to small.
Coil open or shorted.
Wrong coil.
Check coil number.
Mechanical obstruction.
With power off, check for free
movement of contact and armature
Pushbutton contacts not
Clean or replace if badly worn.
Interlock or relay contact
not making.
Adjust or replace if badly worn.
Loose connection.
Turn power off first, then check
the circuit visually with a
Overload relay contact open.
Wire may be
2. Contactor or Relay Does Not
Pushbutton not connected
Check connections with wiring
Shim in magnetic circuit (DC
only) worn, allowing
residual magnetism to hold
armature closed.
Interlock or relay contact
not opening circuit.
Adjust contact travel.
“Sneak” circuit.
Check control wiring for
insulation failure.
Gummy substance on pole
Clean with solvent.
Worn or rusted parts causing
Replace parts.
Contacts weld shut.
See Item 3.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 5-2. Motor control trouble-shooting chart-continued.
3. Contacts weld shut or
Insufficient contact spring
pressure causing contacts to
burn and draw arc on closing.
Very rough contact surface
causing current to be carried
by too small an area.
Adjust, increasing pressure.
Replace if necessary.
Smooth surface or replace if
badly worn.
Abnormal inrush of current.
Use larger contactor or check
for grounds, shorts or
excessive motor load current.
Rapid jogging.
Install larger device rated
for jogging service or caution
Low voltage preventing magnet
from sealing.
Foreign matter preventing
contacts from closing.
Short circuit.
Correct voltage condition.
Check momentary voltage dip
during starting.
Clean contacts with approved
Remove short circuit fault and
check to be sure fuse or
breaker size is correct.
Contact Chatter
Broken pole shader.
Poor contact in control
Improve contact or use holding
circuit interlock (3-wire
Low voltage.
Correct voltage condition.
Check momentary voltage dip
during starting.
5. Arc Lingers Across
If blowout is series, it may
be shorted.
If blowout is shunt, it may be
open circuited.
Arc box might be left off or
not in correct place.
If no blowout used, note
travel of contacts.
Check wiring diagram to see
kind of blowout.
Check wiring diagram through
See that arc box is on
contactor as it should be.
Increasing travel of contacts
increases rupturing capacity.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 5-2. Motor control trouble-shooting chart-continued.
6. Excessive Corrosion of
Chattering of contacts as a
result of vibration outside
the control cabinet.
Check control spring pressure and
replace spring if it does not give
rated pressure.
If this does not
help, move control so vibrations are
High contact resistance
because of insufficient
contact spring pressure.
Replace contact spring.
Abnormally Short Coil Life
High Voltage.
Check supply voltage and rating of
Gap in magnetic circuit
(alternating current only).
Check travel of armature. Adjust SO
magnetic circuit is completed.
Ambient temperature too high.
Check rating of contact. Get coil
of higher ambient rating from
manufacturer, if necessary.
Filing or dressing.
Do not file silver-faced contacts.
Rough spots or discoloration will
not harm contacts.
Interrupting excessively high
Install larger device or check for
grounds, shorts or excessive motor
Use silver-faced
Excessive jogging.
Install larger device rated for
jogging or caution operator.
Weak contact pressure.
Adjust or replace contact springs.
Dirt on contact surface.
Clean contact surface.
Short circuits.
Remove short circuit fault and check
for proper fuse or breaker size.
Loose connections.
Clean and tighten.
Sustained overload.
Install larger device or check for
excessive load current.
8. Panel and Apparatus Burned
by Heat From Resistor
Motor being started frequently
Use resister of hiqher rating.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 5-2. Motor control trouble-shooting chart-continued.
Coil Overheating
Overvoltage or high ambient
Check application and circuit.
Incorrect coil.
Check rating and replace with
proper coil if incorrect.
Shorted turns caused by
mechanical damage or
Replace coil.
Correct pole faces.
Undervoltage, failure of
magnet to seal in.
Clean pole faces.
Dirt or rust on pole faces
increasing air gap.
Overload Relays Tripping
Sustained overload.
Check for grounds, shorts or
excessive motor currents.
Loose connection on load
Clean and tighten.
Incorrect heater.
Relay should be replaced with
correct size heater unit.
11. Overload Relay Fails to
Clean or replace.
Mechanical binding, dirt,
corrosion, etc.
Wrong heater or heaters
omitted and jumper wires used.
Motor and relay in different
Check ratings.
Apply proper
Adjust relay rating
accordingly or make
temperature the same for both.
Noisy Magnet (Humming)
Broken shading coil.
Replace shading coil.
Magnet faces not mating.
Replace magnet assembly or
Dirt or rust on magnet faces.
Clean and realign.
Low voltage.
Check system voltage and
voltage dips during starting.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
6-1. Components.
Power cables are generally made up of three
components: conductor, insulation and protective
covering. The single most important component of a
cable is its insulation. The best way to ensure continued reliability of a power cable is through visual
inspection and electrical testing of its insulation.
The guidance provided here applies only to cables
rated 600V AC or less and, to the occasional applications found in DC motor drives operating at 500,
600, or 700v DC or less.
6-2. Visual inspection.
A visual inspection of a power cable can be made
with power on. However, if the visual inspection is
to include touching, handling or moving cables in
manholes or at terminations, then all circuits in the
group to be inspected should be de-energized before
the work is started.
a. Manhole installations. Manholes are not usually located inside buildings. Terminations and
splices of non-lead cables should be squeezed in
search of soft spots, and inspected for tracking or
signs of corona. The ground braid should be inspected for corrosion and tight connections. Inspect
the bottom surface of the cable for wear or scraping
due to movement at the point of entrance into the
manhole and also where it rests on the cable supports. Inspect the manhole for spalling concrete or
deterioration above ground. If the manhole is
equipped with drains, these may require cleaning
or, in some instances, it may be necessary to pump
water from the manhole prior to entrance. Do not
enter a manhole unless a test for dangerous gas has
been made and adequate ventilation gives positive
assurance that entry is safe. High voltage cables
may be present fireproofed with asbestos containing
materials which pose additional health hazards.
Potheads should be inspected for oil or compound
leaks and cracked or shipped porcelains. The
procelain surfaces should be cleaned and if the connections are exposed, their tightness should be
checked. Since inspection intervals are normally
one year or more, comprehensive records are an
important part of the maintenance inspection. They
should be arranged so as to facilitate comparison
from one year to the next. Cables in manholes,
ducts or below grade installations should be inspected for the following:
(1) Sharp bends in the cables.
(2) Physical damage.
(3) Excessive tension.
(4) Cables laying under water.
(5) Cable movement or dangling.
(6) Insulation swelling.
(7) Soft spots.
(8) Cracked protective coverings.
(9) Damaged fireproofing.
(10) Poor ground connections or high impedance to ground.
(11) Deterioration of metallic sheath bond.
(12) Corrosion of cable supports or trays.
b. Raceway and cable tray installations. Since the
raceway or cable tray is the primary mechanical
support for the cable, it should be inspected for
signs of deterioration or mechanical damage. The
cable jacket should also be checked for abrasions or
mechanical damage.
6-3. Cable insulation testing.
The electrical test most often conducted to determine the quality of low voltage cable insulation is
the insulation resistance test (para 14-2). It is performed as a routine maintenance test for cables
already in service or as an acceptance test for new
cables. DC overpotential testing is another way of
testing cable insulation. This test is performed primarily on medium and high voltage cables to test
their dielectric strength and is not recommended for
routine maintenance testing of low voltage cables.
The insulation resistance test for low voltage cables
is usually performed using a megohmmeter (para
13-4). It is a simple, quick, convenient and nondestructive test that can indicate the contamination of
insulation by moisture, dirt or carbonization. Before
testing any cable, the circuit must be de-energized.
Once that is done, it is usually best to disconnect
the cable at both ends in order to test only the cable,
and to avoid error due to leakage across or through
switchboards or panelboards. For an acceptance
test, cable less than or equal to 300 V maybe tested
at 500 V and cable greater than 300 V but less than
600 V maybe tested at 1,000 V. For a routine maintenance test, test voltage should be restricted to 60
percent of the factory test voltage. The test voltage
should be applied from phase to ground on each
conductor with the shielding tapes and metallic
jackets also connected to ground (fig 6-l). While no
general standard exists for minimum acceptable insulation resistance values for cables in service, a
“rule-of-thumb” of one megohm of resistance (mini6-1
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 6-1. Connections for Testing Low Voltage Cable Insulation: a) Test on single-conductor cable, b) Tests on multi-conductor cable.
mum) per 1,000 V of applied test voltage is accepted. If a cable should fail the test, then further
cable testing is required to pinpoint the failure location. A cable locator/fault finder can trace the exact
path of buried or above ground cable and locate a
fault. The insulation resistance test should be performed at regular periods and a record kept of the
readings. Insulation resistance decreases with an
increase in temperature. Thus, in order to properly
interpret the results and to permit a reliable comparison of periodic readings, the readings should be
corrected to a base temperature. Correction factors
and methods are shown in the reference material of
the megohmmeter manufacturer. It should be noted
that persistent downward trends in insulation resistance indicate insulation deterioration even
though the readings may be higher than minimum
acceptable values.
6-4. Overpotential testing.
Both direct current (DC) and alternating current
(AC) overpotential testing practices require the use
of high voltages. Only properly trained, competent
shop personnel should perform such tests. Because
of the extra time, manpower and expense needed for
overpotential testing, it is not recommended as a
routine scheduled maintenance tool. The test is
done mainly to seek out weaknesses in the cable
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 6-1. (Continued) c) Use of the “guard” terminal to eliminate measure of surface leakage across exposed insulation at
one end of cable, d) Use of a “spare” conductor to guard both ends of a multi-conductor cable, e) Use of "guard” to
eliminate all surface leakages except conductor under test.
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
Figure 6-1. (Continued) f) Connection for testing total resistance between one conductor and all others plus ground, g) Testing one
conductor leakage to ground only, h) Testing one conductor to others in the bundle-leakage to ground eliminated by guard.
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
insulation system that otherwise may not show up
during insulation resistance testing. Overpotential
testing may be desirable as an overall quality acceptance test after installation, modifications, or expansion of a feeder cable system; as an additional
check of critical, emergency power feeder cables; as
an additional quality check that is known to have
conducted high current due to a short circuit fault
in the connected equipment; or, as a quality check
after cable splices have been made. Overpotential
testing is not recommended as a periodic, routine
maintenance test under three conditions. First, if
the cable cannot be completely disconnected or isolated from the connected load(s) or auxiliary devices
such as surge capacitors, lightning arresters, fuses,
cutouts, and switchgear bus, second, if unacceptable
readings have already been obtained from general
insulation resistance testing, and third, if the cables
are known to be laying under water.
a. Direct current (DC) tests. There are two methods used for DC overpotential testing. In the first
method, the voltage is raised gradually to the specified level. The rate of increase should be adjusted to
maintain a steady charging and leakage current.
The current for a DC testis measured in microampere. Sixty to ninety seconds has been found to be
an acceptable average time to reach the final test
voltage level. When this level has been reached,
leakage current readings are taken and recorded at
O, 1, 2, 3, 4, and 5 minutes. After the last reading,
the voltage is slowly lowered and the cable is allowed to fully discharge. The second method is
called the step method. Using this procedure, the
test voltage is raised in steps at given intervals. The
leakage current is measured and recorded at each
new voltage level as well as the O, 1, 2, 3, 4 and 5
minute intervals after the final test voltage has
been reached. The step method is intended to catch
an undesirable trend in the leakage current before
the cable actually fails. The test can be stopped
before the final voltage is reached. An engineering
judgment will be required to determine if the cable
should be left in service or if remedial measures
should be taken. In both test methods, good interpretation of the leakage current magnitudes and
the trends is necessary. Temperature, humidity, and
insulation surface conditions affect the readings.
Table 6-1 should be used as a guide in determining
the specified test voltages.
b. Alternating current (AC) tests. AC overpotential testing is severe and possibly destructive to
the cable under test. In the AC test, the voltage is
quickly raised from zero to the specified level. The
test is usually held for one minute. The current is
measured in milliamperes; however, its value is not
important. The reading of current is provided so
that the person running the test can determine if
the particular test set has sufficient capacity for the
task at hand. If the cable withstands the one
minute application, the test has been passed. Failure results in short circuit and a ruined portion of
the cable. The test set is designed to trip off immediately upon detection of the fault current. Table
6-1 gives the recommended test levels.
6-5. Cable trouble-shooting.
Table 6-2 provides information regarding the most
common cable failure: overheating. Probable causes
of overheating cables are listed along with recommended practices to remedy the problems.
Rated Circuit
Voltage, Phase
to Phase, Volts
Size AWG or
100 Percent
Insulatation Level
133 Percent
Insulation Level
100 Percent
Insulation Level
233 Percent
100 Percent
233 Percent
Insulation Level
Insulation Level
Insulation Level
* MCM-Thousands of circular mils.
100 percent level - Cables in this category may be applied where
the system is provided with relay protection such that ground faults
will be cleared as rapidly as possible, but in any cause within 1
minute. While these cables are applicable to the great majority of
cable installations which are on grounded systems, they may be used
also on other systems for which the application of cables is
acceptable provided the above clearing requirements are met in
completely de-energizing the faulted section.
133 Percent Level - This insulation level corresponds to that formerly designated for
ungrounded systems. Cables in this category may be applied in situations where the clearing
time requirements of the 100 percent level category cannot be met, and yet there is adequate
assurance that the faulted section will be de-energized in a time not exceeding 1 hour. Also
they may be used when additional insulation strength over the 100 percent level category is
(IPCEA S-68-51G, NEMA WC 8-1971).
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
Table 6-2. Cable maintenance--overheating problems.
Cause of overheating
Instal lat ion
Cables in racks
Heat from lower cables
in vertical racks
rises and heats upper
Cables spaced
horizontally affected
by mutual heating.
or in a
heat is
as near
closely spaced
location where
confined, s u c h
External sources of
Provide baffles to deflect
rising warm air.
Increase space between cables.
(For beat cooling, minimun
between cables should be twice
the cable diameter).
If constricted portion of cable
run is short, fans can be set
up to provide cooling.
Re-route cable or remove heat
Shield cables from heat or
ventilator with fan.
Cables in floor
Mutual heating of
cables that have been
piled aimlessly in
overcrowded floor
Restriction of air
circulation by solid
covers on channels.
Cables in tunnels
Mutual heating of
cables spaced too
closely on rack.
Rack cables systematically and
maintain spacing necessary to
minimize mutual heating.
replace solid
Where practical,
covers with perforated covers
to increase air circulation.
Re-route part of load from
overloaded cables to cables
carrying lighter loads.
Space cables on racks to
minimize mutual heating.
cables near the floor.
Force air circulation
External sources of
Insulate adequately from the
external heat source.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 6-2. Cable maintenance--overheating problems--continued.
Cables in
Cause of
addition of
loaded cables to
duct bank without
reducing the
rating of cables
already in bank
Transfer load from
overloaded cables to
cables carrying lighter
loads. Place power
cables in outside ducts
with most heavily loaded
cables at the corners of
Install ventilating
covers on congested
(A fan to force air out
through a ventilating
cover may help).
Cables buried
in earth.
Wetting dry soil improves
its conductivity, and may
slightly improve cable
capacity. Only real
remedy is transferring
portion of load to
another circuit.
Aerial Cables
Reduce load.
Cable in hot sun.
If practical, shade from
Capacity can be increased
15 percent by separating
cables installed in one
Cable Risers
Cable chosen for
operation instead
of in a conduit
in air.
Provide fans to cool
risers during overload
Heating air
rising and
trapped at top of
Provide ventilating
bushing at top of
Exposure to sun.
Shade risers, if
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 6-2. Cable maintenance--overheating problems--continued.
Cause of
High current
equipment, and
low voltage at
receiving end.
Install capacitors to
improve power factor.
Raise voltage by means of
taps on transformer or
reduce voltage drop by
moving single-conductor
cables closer together.
Move transformer closer
to load.
If load can be operated
at two voltages, use
higher value.
currents because:
loading of
phases, and
arrangement of
cables in group.
Balance arrangement of
single-phase loads to
divide current equally
between three conductors.
With two or more singleconductor cables in
parallel per phase,
consideration must be
given to phase
arrangement of cables to
prevent unbalanced
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
7-1. Solid-state maintenance.
Electronic system maintenance is required for
proper operation. Specific maintenance procedures
should be obtained from the equipment manufacturer. Preventing the solid-state component from
failing will increase the electronic system’s availability. Preventive maintenance applied to electronic systems should be directed toward minimizing the chance of component failures thereby
reducing the causes of system failure. There are two
primary causes of solid-state component failure.
First is heat caused by overloading, surface contamination or poor ventilation. The second is vibration caused by mechanical stress, shock, moisture
due to environment, overvoltage, electrical spikes
or static discharge while handling components.
a. Preventive measures. The following are general
preventive measures applicable to individual equip
ment within a system. Detailed preventive maintenance of specific solid-state components is covered
later in this chapter.
(1) Keep equipment clean. Limit overheating
and the chances of current leakages or flashover by
periodic vacuuming or blowing out dirt, dust, and
other surface contaminants from the equipment enclosures. Use a non-conducting nozzle on the
vacuum or air hose (a metal nozzle can cause component damage and/or breakdown). Do not use high
pressure air, it may damage components.
(2) Keep equipment dry. Space heaters will prevent the accumulation of moisture and subsequent
corrosion thereby limiting intermittent component
(3) Keep equipment tight. Tight connections
and secure leads and contacts limit adverse effects
of vibration.
(4) Keep equipment cool. Proper ventilation
limits overheating due to high ambient temperature.
b. System checks. The following are basic system
checks which may be applicable to components and
subassemblies within a given system.
(1) Magnetic device. Check the operation of
magnetic and contact-making devices in accordance
with applicable instructions. Brushes in motors
(used for all motor driven position adjusters, etc.)
and all exposed brushes or contact buttons for
rheostats, potentiometers, and variable transformers should be inspected every 12-18 months. For
frequent operations or adverse operating conditions,
such as very dusty, humid, and corrosive areas, inspections may have to be done every 4-6 months. If
arcing occurs, or if the brushes are badly worn,
replacement is recommended.
(2) Input and output. Input and output signal
voltages, which can be considered important indicators of operating conditions, should be checked on
the regulator or function panels. A high input impedance voltmeter should be used for these measurements. The checks should be performed every
12-18 months. Data should be recorded for future
reference and the test points where the data was
taken should be fully explained.
(3) Semiconductor-controlled rectifier (SCR).
Spot check operation of SCR’s by observing their
neon lamp monitors. All lamps should either glow or
not glow as a group. When lighted, all lamps should
glow with about the same intensity with one electrode in each lamp glowing somewhat more brightly
than the other.
(4) Planned outages. For planned outages, the
following maintenance should be performed:
(a) General cleaning with either low pressure, dry air and/or a vacuum cleaner. Any air intake filters should be inspected, cleaned if possible,
or replaced at this time.
(b) Check all brushes, small auxilliary motors, variable slide-wire resistors (rheostats), potentiometers, and variable transformers.
(c) Inspect all control and power relays for
freedom of operation and the condition of their contacts. Also, check for failed surge suppression devices when these are provided across the operating
coil connections.
(d) Check for any loose connections or evidence of heating on large cable, bus, and large
SCR’s or rectifiers. Correct cause when found.
(e) Check SCR or rectifier legs and corresponding fuses with an ohmmeter. Test all elements
of parallel groups individually.
7-2. Solid-state components.
Maintenance procedures for solid-state component
are designed to detect evidence of abnormal heating, moisture, dust and other contaminants; promote good reliability and minimize downtime; prolong the useful life of the equipment; and, recognize
repeated component failures and take corrective actions.
a. Static testing. For this work, static testing is
taken to mean one or more electrical tests, performed on a given component, using very low voltages or powers. Furthermore, these tests are designed to give a very general idea as to the
component’s overall condition and not its perfor7-1
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
mance per published specifications. To test most
capacitors, rectifiers (diodes), resistors, potentiometers, SCR’s, and bipolar junction transistors, the
volt-ohmmeter (VOM) is the recommended instrument (para 13-2). There are many types and models
available; however, the analog meter still serves
very well for static testing. It should be noted that
meters with very low energy resistance test ranges
will not produce the same results described in the
paragraphs below. Most all new digital models have
the low energy resistance test feature. The manufacturers have recognized this problem and usually
provide one additional function marked “diode test”
or simply the ANSI symbol for a diode. This type of
test is also different from those described below. The
diode test feature differs from the resistance test,
using an ohmmeter, in that the instrument generates a freed current (about 10-100 milliamperes)
and passes it though the device under test. The
corresponding voltage generated across the device
terminals is usually the reading that appears on the
instrument’s display. The maximum voltage is
never more than the battery voltage used to power
the meter. The ohmmeter applies a relatively constant voltage and allows the current to vary in proportion to the total circuit resistance (Ohm’s Law).
Before testing, the ohmmeter must be calibrated for
zero ohms. This nulls out the test lead resistance;
the test probes are touched together and the meter
reading is adjusted to indicate zero. Then, the particular component to be tested must be isolated
from the rest of the circuit. This is done by disconnecting at least one lead of the component.
b. Capacitors. A capacitor stores electrical energy
for dissipation as needed in an electrical circuit. The
amount of charge stored depends upon the value of
the capacitor (expressed in pico-, nano-, or microfarads) and the applied voltage. There are many types
of capacitors used in power electronic and control
equipment (fig 7–l). The more commonly used types
are: oil-impregnated and non-polarized; polarized
aluminum electrolytic; polarized wet slug and
dipped tantalum; non-polarized wet slug and dipped
tantalum; and, non-polarized paper, plastic film,
mica, or ceramic capacitors. A capacitor is defective,
or will soon be defective if it has a damaged case, is
leaking fluid or electrolyte paste, or testing shows it
to be nearly shorted or completely open.
(1) Inspection for oil leaks. Leaking capacitors
can be found by locating the oil or fluid that has
seeped from a cracked case or relief plug. A leaking
capacitor may be kept in service for brief emergency
periods but should be replaced before it fails altogether, or the leaking fluid damages other equipment. Before rejecting a capacitor for leaking oil, be
sure the oil was not deposited by some other appa7-2
ratus or another capacitor located above. An effort
should be made to determine the nature of the leaking fluid. If the capacitor is not specifically
stamped: “NON-PCB” or “NO PCB’s”, then the
Hazardous Waste Coordinator should be contacted
and the capacitor disposed of as recommended by
that Office.
(2) Testing. Open or solid capacitors maybe
found by using an ohmmeter to test as follows:
(a) Identify the polarity of the terminals
when electrolytic capacitors are to be tested. Always
test with the plus (+) lead of the meter connected to
the terminal marked plus (+) or the red dot. Reversed polarity, even at low voltages, causes high
dissipation in the electrolyte paste and gives poor
test readings on a possible good unit.
(b) For values under one (1) microfarad, use
the “X1OO” scale. For higher values, use either the
"X100” or the "10X" scale.
(c) Discharge the capacitor before testing.
Use a 100-1000 ohm resistor to limit the discharge
current. Remove the resistor connection.
(d) Connect the test probes and note the
meter deflection. If the capacitor is open, the ohmmeter will continually indicate infinity ohms. The
meter needle will not move the moment the leads
are touched to the capacitor terminals. Replace capacitors that are open circuit. If the capacitor is
shorted, the meter needle will immediately deflect
to zero or some low value and remain there. Replace
capacitors that are shorted. A good capacitor will
cause the meter needle to deflect toward zero ohms
the moment the leads are touched to its terminals.
However, the needle will begin to indicate everincreasing resistance as the capacitor charges up.
The amount of initial deflection and the rate of
return of the needle depend on the value of the
capacitor and the ohms scale multiplier selected.
Capacitors that are “leaking electrically” will cause
the meter needle to deflect as usual; however, the
final resistance value may be only several hundreds
of ohms rather than the several thousands that can
be expected. Capacitors not properly isolated from
the circuit during the test often give this kind of
reading because of the other components connected
in parallel. If it is certain the capacitor alone is
reading this way, it should either be replaced or
retested with an analyzer. All of the test results
described above will be more readily understood if
several values of capacitors that are known to be
good are tested first.
c. Rectifiers and semiconductor-controlled rectifiers (SCR). A rectifier (diode) is a solid-state device
that limits the flow of electrical current to one direction. The semiconducting material within the device
acts as an insulator in one direction (within certain
TM 5483/NAVFAC M-116/AFJMAN 32-1083
Figure 7-1. Typical
Capacitor Types: a) Oil-filled AC, snubber capacity b) Electrolytic,
ceramics and plastic film types for DC
voltage limits) and as a fairly good conductor to
current flow in the opposite direction. The ohmmeter may be used to measure the forward resistance
(conduction) and the reverse resistance (insulating
or blocking) of the device in order to determine its
overall condition. Testing should be done as shown
in figure 7–2c. Connect the ohmmeter to read resistance in the forward direction. The reading should
range between 6-35 ohms. This is the range for
general purpose rectifiers. Very small, signal type
rectifiers may read as high as 70-100 ohms. Very
large current capacity rectifiers may read between
five and ten ohms. Finally, germanium diodes read
lower than those made from silicon, and fast recovery types read lowest of all: two to six ohms. Connect the ohmmeter to read resistance in the reverse
direction. The reading obtained should be between
10,000 and 100,000 ohms or possibly more. The
reading tends to be near the lower end of the range
for large current capacity types. If the diode is good,
the values listed above will be obtained. Readings of
one (1) ohm or less mean the device is damaged or
shorted. Reverse direction readings less than 10,000
ohms generally mean the device is damaged or electrically leaking. In both cases, the unit should be
(1) Semiconductor-controlled rectifier (SCR).
The SCR is a diode with the ability to be forced into
conduction by the application of a gate signal. The
SCR cannot conduct in the reverse direction if it is a
good unit. However, the SCR will not conduct in the
forward direction either until a small gate voltage is
applied. Once in conduction, the SCR remains that
way until its current (not the voltage) drops below
the minimum holding value for that particular device. The SCR should be tested like the diode rectifier (fig 7–2d) but with the following modifications
to the procedure:
(a) Connect the ohmmeter to read forward
resistance. The meter needle should read infinity
ohms before a gate-cathode voltage is applied. Connect an additional voltmeter between the gate and
cathode leads of the SCR. Apply an adjustable DC
voltage to these leads and measure the voltage
needed to start conduction. The ohmmeter will give
readings like those for the diode when conduction
has been established. Note the gate-cathode voltage
when conduction starts. It should be between 0.6
and 1.3 volts for the most general purpose units.
(b) Disconnect the gate lead. The SCR will
remain in conduction until the ohmmeter leads are
removed. This condition depends on two things:
first, the particular SCR must have a very low holding current; second, the battery in the ohmmeter
must be fresh or fully recharged. A gate to cathode
resistance check may be applied also. With plus (+)
on the gate, the ohmmeter reading will be similar to
the diode forward reading. There is no blocking
reading for the reverse. Readings for the cathode to
gate connection are generally only 10-50% higher
than those obtained in the forward mode. If a test
battery (fig 7–2d) is not available for the conduction
test, an alternate test can be done using only the
ohmmeter. This simplified test is harder to interpret and is less accurate than the procedure described above. To do the test, setup as in paragraph
(a) above. In place of the test battery, touch the gate
lead to the anode (+) lead. The SCR should begin to
(2) Other devices. There are many styles and
types of devices for both diodes and SCR’s. It is beyond the scope of this manual to describe all of them
in detail. several case styles (T62, T72, DO-200, and
TO-200 for diodes, and R62, R72, and T9G for SCR’s)
are designed to operate clamped between heat sinks.
There is a spring contact within the device that prevents operation unless the unit is physically compressed. These devices should be tested in place if
possible. Otherwise, moderate pressure applied with
the fingers is usually sufficient to “make” the internal connection. Apiece of insulating material should
be placed between the fingers and SCR surface to
prevent false leakage readings.
d. Resistors and rheostats. A resistor is a passive
component used to hinder the flow of electric current. Many sizes, shapes, values and types of resistors are available. The most common types are wire
wound (resistance wire wound around an insulator)
and carbon stick (pressed carbon tubes or rods). A
rheostat is simply a variable resistor. Like resistors,
rheostats also are made in numerous sizes, shapes,
values and types. Again like the resistor, the
rheostats are wire wound or carbon composition.
The rheostat is normally 3/4 circular in design with
a terminal at each end. A movable contact or brush
known as the “wiper” rides on the rheostat material
surface and can be moved to select the desired resistance value. Use an ohmmeter to accurately
measure the resistance of a resistor or rheostat.
However to avoid false readings of devices which
may be connected in parallel, disconnect one side of
the component to be tested before making resistance measurements. Replace components that do
not measure within plus or minus five percent of
the value given in the manual or as specified on the
schematic diagram, unless other tolerances are indicated. Replace broken, cracked or damaged units
and support brackets.
e. Zener diodes. A Zener diode is a semiconductor
device like the rectifier diode, but the Zener device
has its composition and P–N junction characteristics carefully controlled in order to produce a de-
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
Figure 7-2. Diodes and SCR’s: a) Various package styles, b) symbols and polarity, c) Testing a Diode, d) Testing an SCR.
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
sired breakdown voltage in the reverse direction.
The Zener diode will provide rectification in its forward mode; however, the precise voltage developed
across its reverse junction is of greater interest.
This property is useful as a voltage reference. No
significant reverse current flows until the Zener
voltage (V) is reached. At this point, a sharp increase in reverse current occurs as illustrated in
figure 7-3 characteristics “A” and "B". The device
will maintain its voltage over a considerable range
of reverse current. It should be noted that any di-
ode, but especially Zener diodes, should be operated
with some means of external series resistance in
order to limit the maximum current flow to within
the rating of the device. The Zener diode can be
manufactured to produce reverse breakdown
(Zener) voltages from 0.5-100.0 volts or more with
power ratings from 025W—100W. The Zener diode
is teated like the general purpose rectifier diode;
however, its Zener voltage (V) cannot be determined
using the ohmmeter tests. An external test voltage
must be applied to determine V (fig 7-4).
-550V. . . -1OV.
Figure 7-4 Testing Zener Voltage.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
f. Transistors. Transistors are three terminal,
solid state devices constructed so that the current
across the base-emitter junction will control a
greater amount of current crossing the collectoremitter junction. Because a smaller current can
control a larger one, the transistor provides gain or
amplification. Transistors vary in size, power, and
voltage ratings. Some idea of the electrical values,
type, and application of the transistor in the circuit
should be known before testing is attempted.
(1) Testing. The bipolar junction transistor
(BJT) is tested just like the general purpose rectifier
diode. These transistors are actually two diode junctions combined in such a way as to obtain current
control. General purpose transistor testing is done
as follows (fig 7-5):
(a) Check the polarity of the test leads and
zero the ohmmeter.
(b) Determine the type of transistor to be
tested, that is whether it is a positive, negative,
positive (PNP) or a negative, positive, negative
(NPN) junction type.
(c) Set the scale multiplier to “X1” or “L0”
and recheck for zero ohms.
(d) Test all combinations as shown in the
diagrams and tables given in figure 7-5a or 7-5b.
(e) Test all combinations as shown with the
scale multiplier set to "X100” or “H1”. If the values
shown in the tables are not obtained, the transistor
part number should be checked to confirm its type,
or the unit should be replaced if the type is known
to be correct.
g. Other solid-state devices. There are numerous
other types of solid-state devices used in modern
electronic and control systems. Most of these cannot
be statically tested with an ohmmeter and expected to give meaningful results. The following is a
brief list of devices that yield valid test results only
in a circuit:
(1) Field-effect transistors (FETs), metal-oxide
semiconductor field-effect transistors (MOSFETS),
or insulated-gate field-effect transistors (IGFETs).
(2) Unijunction Transistors (UJTs) or Programmable Unijunction Transistors (PUTs).
(3) Analog Operational Amplifiers and Integrated Circuits.
(4) Any class of Digital Logic Integrated Circuit.
7-3. Electrical disturbances (power quality).
Equipment with sensitive electronic circuits (digital
clocks, VCRs, computers, data terminals) may experience memory loss, system malfunction and even
component failure due to electrical power source
disturbances. Sags, surges and harmonics are some
common types of disturbances. Disturbances caused
by other customers or even by customer’s own
equipment may also affect customer’s equipment.
“Power quality” is a relatively new term used to
describe the quality of power (absence of voltage
dips, surges, harmonics outages, frequency variation) at the user’s location. Traditional measurements for reliability studies don’t deal with the
power quality needs of sensitive electronic equip
ment. Rather, they deal with the permanent or prolonged outage and how to improve upon it. While
this is indeed important to sensitive loads, there is
increased concern for short term or momentary disturbances. In addition to voltage limits, sensitive
loads such as computers typically require the frequency to be within plus or minus .05 Hz, the rate of change of
frequency less than 1 Hz/sec, voltage waveform distortion under five percent and voltage unbalance
less than three percent. For specific applications,
the power quality requirements should be obtained
from the manufacturer of the sensitive equipment.
Some of the common types of disturbances, the
symptoms, causes and effects are summarized in
table 7-1.
7-4. Disturbance measurement and monitoring.
Conditions may be quite different at any given site,
and it is desirable to obtain specific data about the
actual situation, if possible, before considering a
remedy. If it is an existing site, it is useful to obtain
any historical data which might correlate sensitive
equipment operation with power disturbances. The
type of data includes the sensitive equipment operating log and maintenance records, and electric utility operating log and voltage recordings.
a. The most useful activity for any existing site is
to conduct a site power line disturbance study for a
one or two month period-including the storm season, if possible. The monitoring should be at the
same point that powers the sensitive equipment
and must use equipment capable of recording the
types of transients that can affect sensitive loads.
b. There are several types of equipment designed
to perform this monitoring function. Unlike the traditional strip or circular chart recorders, this equipment is capable of recording variations of voltage in
the short time periods of interest for sensitive
equipment, yet operate continuously for weeks at a
time. Much of the equipment is of the digital readout type which, unfortunately, can lead to improper
interpretation of the conditions at the site because
it cannot always distinguish between harmless and
harmful disturbances.
c. Much more useful monitors produce an analog
recording of the disturbances with the ability to
expand the waveforms to examine them in detail.
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
Figure 7-5. Transitor Testing: a) PNP type, b) NPN type.
With this data, it is possible to determine if a disturbance is harmful or not by comparing it with
specific tolerance requirements for the sensitive
equipment actually used on site. This tolerance information is generally available from sensitive
equipment manufacturers upon customer request.
With the expanded waveform capability, it is often
possible to examine transients and observe a characteristic “signature” which will identify the source
of the disturbance.
7-5. Voltage surge suppression.
Voltage surges on a power system are a common
power problem experienced by sensitive electronic
equipment and mostly seen by the computer user.
These transients can be the cause of lost data, false
triggering and equipment failure. These transients
are generated both internally by the user and externally on the utility primary due to lightning and
equipment switching. Many different types of volt-
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 7-1. Power quality problems summary.
Sags -
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
age suppressors, filters, etc. are used to protect the
sensitive electronic equipment. These types of
equipment are called power conditioners.
a. Transient suppressors. Transient suppressors
are very low cost devices available for microcomputers in the form of outlet strips similar to extension
cords with multiple receptacles. They usually contain metal oxide varistors (MOVS) and sometimes
silicon avalanche diodes (SADS). These are typically
disc shaped devices connected between the power
lines and, sometimes, from line to ground. They
absorb energy from transients which exceed their
threshold (typically 100 percent above normal peak
voltage). Because of their small size and low cost
compared with the equipment they serve and the
cost of determining if such transients exist at a
given installation, many people provide this protection as insurance. This type of transient suppressors can be provided for a nominal cost and most of
the more expensive power conditioners such as line
voltage regulators, static switches and UPS systems
have these devices built in. They can even be added
to a distribution panelboard, if not included elsewhere. Another form of transient suppressor, a
surge arrester, is intended to lower the transient
energy level to that which can be handled by downstream power conditioners, such as MOVS or filters.
They typically use gas discharge tubes which are
slower acting than MOVS, but can absorb more energy. To be effective, however, they too must be
coordinated with upstream surge arresters having
greater energy absorbing capability. Usually, this is
done at each point of voltage transformation back to
the incoming line and is best coordinated with the
electric utility. Packaged transient suppressor systems combining the devices described above are
available which, when properly installed, will limit
expected surges as defined by the IEEE Standard
b. Filters. Line filters are used to reduce electromagnetic interference (EMI) and/or radio frequency
interference (RFI) to acceptable levels. Generally
small and low in cost, they, too, are usually built
into sensitive equipment and the more expensive
power conditioner equipment. The simplest form of
filter, a low pass filter, is designed to pass 60 Hz
voltage but to block the very high frequencies or
steep wavefront transients. They are not effective
for frequencies near 60 Hz, such as low order harmonics, but become effective in the Khz range. Filters can be connected line to line or line to neutral
for rejection of normal mode noise. They can also be
connected line to ground for common mode noise
rejection. Some of the better transient suppressor
outlet strips also contain these falters.
c. Isolation transformers. Isolation transformers
are more expensive power conditioners. They provide two functions. One is the ability to change to a
new voltage level and/or to compensate for high or
low site voltage. For example, by using 480V input
up to the point of use and then transforming to
120V or 208Y/120V, the switchgear and wiring can
be reduced in size and the effect of line drop reduced. If the voltage at the point of use is too low
due to line drop, it can be manually boosted in steps
by connecting to different taps on the transformer
windings. The second function of the isolation
transformer is to provide for the ground reference
right at the point of use. This eliminates the problem of common mode noise induced through “ground
loops” or multiple current paths in the ground circuit upstream of the established reference ground
d. Voltage regulators. Most of the voltage problems except outages can be handled by the addition
of voltage regulators equipped with transient suppressors. Several solid-state techniques have been
developed in recent years to replace the older, slow
acting electro-mechanical type. One type of fast response regulator is the phase modulating type. It
usually utilizes thyristor (SCR) control of buck and
boost transformers in combination with filters to
provide stable sinusoidal output even with nonlinear loads typical of computer systems. This is
done in a smooth continuous manner, but at great
speed, eliminating the steps inherent in the tap
changer. Heavy loads can be delivered for start-up
inrush typical of computer central processors or disc
drive motors while maintaining full voltage.
e. Motor generators. Motor generators consist of
an electric motor driving an AC generator so that
the load is electrically isolated from the power line.
Motor generators are used widely as a source of 400
Hz power for large computer central processors requiring this frequency. Because the frequency tolerance of the computers is wide, a simple induction
motor can be used to drive a brushless synchronous
generator (alternator). The speed changes with load
and input voltage variations hold output frequency
well within tolerance and constant voltage is maintained by automatic voltage regulators controlling
the generator’s field excitation.
f. Uninterruptible power supplies (UPS). For continuous operation of computer or other sensitive
systems when line voltage is interrupted, the only
solution is a UPS. A properly designed UPS can
provide computer quality power under essentially
all normal and abnormal utility power conditions
during outages for extended period of time depending on battery capacity. This bridges most power
outages and permits orderly shutdown for longer
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
outages. UPS systems are typically solid-state without any rotating machinery. However, some designs
incorporate motor generator sets in addition to
solid-state circuitry and batteries to supply continu-
ous power. These systems are commonly known as
rotary UPS. A rotary UPS electrical output is usually more sinusoidal than a solid-state UPS and is
less susceptible to distortion.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
8-1. Ground maintenance.
The term grounding implies an intentional electrical connection to a reference conducting body, which
may be earth (hence the term ground), but more
generally consists of a specific array of interconnected electrical conductors. The resulting circuit is
often referred to by several terms, such as: ground
plane, ground grid, mat or ground system. Grounding systems should be serviced as needed to ensure
continued compliance with electrical and safety
codes, and to maintain overall reliability of the facility electrical system. Action must be initiated and
continued to remove, or reduce to a minimum, the
causes of recurrent problem areas. When possible,
maintenance inspections should be performed at
times which have the least affect on user activities.
The complexity of ground systems and the degree of
performance expected from such systems is growing
all the time. Maintenance or shop personnel are
encouraged to become familiar with Article 250 of
the National Electrical Code (NEC), which deals
with grounding requirements and practices.
8-2. Types of grounding systems.
Six (6) types of grounding systems will be described.
They are static grounds, equipment grounds, system grounds, lightning grounds, electronic (including computer) grounds and maintenance safety
grounds. All of these systems are installed similarly.
However, their purposes are quite different. Some of
the systems carry little or no current with no freed
frequency. Others carry small to moderate currents
at 50 or 60 Hz. Still others must be able to carry
currents over a very broad range of frequencies in
order to be considered effective. Most grounding
system troubles are caused by one of two problems: 1) loss of effectiveness due to poor maintenance and, 2) inadequate ground system for the
degree of performance expected.
a. Static grounds. A static ground is a connection
made between a piece of equipment and the earth
for the purpose of draining off static electricity
charges before a spark-over potential is reached.
The ground is applied for more than just the comfort of the equipment operator. The possibility of an
explosion ignited by an electrical spark must be
considered. Dry materials handling equipment,
flammable liquids pumps and delivery equipment,
plastic piping systems, and explosives storage areas
all need static ground protection systems installed
and functioning properly. Static ground systems are
generally not called upon to conduct much current
at any given frequency. Smaller gauge, bare conductors, or brushes with metallic or conductive bristles
make up most parts of the static ground system.
b. Equipment grounds. An equipment ground
pertains to the interconnection and connection to
earth of all normally non-current carrying metal
parts. This is done so the metal parts with which a
person might come into contact are always at or
near zero volts with respect to ground thereby protecting personnel from electric shock hazards.
Equipment grounding consists of grounding all
noncurrent-carrying metal frames, supports and enclosures of equipment. All these metallic parts must
be interconnected and grounded by a conductor in
such a way as to ensure a path of lowest impedance
for the flow of ground fault current from any line to
ground fault point to the terminal at the system’s
source. An equipment grounding conductor normally carries no current unless there is an insulation failure. In this case the fault current will flow
back to the system source through the equipment
grounding conductors to protect personnel from
electrical shock. The equipment grounding conductor must never be connected to any other hot lines.
Equipment grounding systems must be capable of
carrying the maximum ground fault current expected without overheating or posing an explosion
hazard. Equipment grounds may be called upon to
conduct hundreds to thousands of amperes at the
line frequency during abnormal conditions. The system must be sized and designed to keep the equipment surface voltages, developed during such abnormal conditions, very low. An example of this
system is the bare copper wire (green conductor)
connected to the frames of electric motors, breaker
panels, outlet boxes, etc., see figure 6-1 for typical
equipment grounding. Electrical supporting structures such as metal conduit, metal cable trays or
metal enclosures should be electrically continuous
and bonded to the protective grounding scheme.
Continuous grounding conductors such as a metallic
raceway or conduit or designated ground wires
should always be in from the ground grid system to
downstream distribution switchboards to ensure
adequate grounding throughout the electrical distribution system. A typical grounding system for a
building containing significant electrical equipment
and related apparatus is shown in figure 8-2, The
illustration shown depicts three most commonly en8-1
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
countered areas pertaining to the grounding. The
grounding grid and grounding body (earth under
the building) with the ground rods (electrodes and
the water pipe system) are shown. The second part
is the conductors associated with the equipment
ground. Part of the equipment ground is also
formed by the switchgear ground bus.
c. System grounds. A system ground refers to the
condition of having one wire or point of an electrical
circuit connected to earth. This connection point is
usually made at the electrical neutral although not
always. The purpose of a system ground is to protect
the equipment. This ensures longer insulation life
of motors, transformers and other system component A system ground also provides a low impedance path for fault currents improving ground fault
relaying selectivity. In a properly grounded system
the secondary neutral of a power transformer supplying a building or facility is connected to a transformer grounding electrode. The transformer neutral is a part of the service entrance point which
bonds to the grounding electrode system of the
building. According to the National Electrical Code
(NEC) articles 250-81 and 250-83, metal underground waterpipes, metal building frames, encased
electrodes, rods and plates are among the items
that can make up the grounding electrode system of
a building. The NEC article 250-S3 requires that
the size of the grounding electrode iron or steel rod
must be at least 5/8 inches in diameter and driven
eight feet deep. The resistance of the electrode to
ground cannot exceed 25 ohms (NEC 250-84). Otherwise a second electrode should be added and the
distance between the two electrodes must be at
least six feet. However, in some systems the 25
ohms resistance value cannot achieve the goals of
grounding. They require ground resistance values
below ten ohms. According to MIL-STD-l88-12A
ten ohms ground resistance is acceptable. If the
main building load is composed of computers or
sensitive electronic equipment, the earth ground resistance should not exceed five ohms. There are
many methods of system grounding used in industrial and commercial power systems, the major ones
being ungrounded, solid grounding, and low and
high resistance grounding (fig 8-3). Technically,
there is no general acceptance to use any one particular method. Each type of system grounding has
advantages and disadvantages. Factors which influence the choice of selection include voltage level of
the power system, transient overvoltage possibilities, types of equipment on the system, cost of
equipment, required continuity of service, quality of
system operating personnel and safety consideration including fire hazards.
(1) Ungrounded system. An ungrounded system is one in which there is no intentional connection between the neutral or any phase and ground.
Ungrounded system implies that the system is
capacitively coupled to ground. The neutral potential of an ungrounded system under reasonably balanced load conditions will be close to ground potential because of the capacitance between each phase
conductor and ground. When a line-to-ground fault
occurs on an ungrounded system, the total ground
fault current is relatively small, but the voltages to
ground potential on the unfaulted phases will be
high. If the fault is sustained, the normal line-toneutral voltage on the unfaulted phases is increased
to the system line-to-line voltage (i.e. square root of
three (3) times the normal line-to-neutral value).
This, over a period of time, breaks down the line-toneutral insulation and hence results in insulation
failure. Ungrounded system operation is not recom-
mended because of the high probability of failures
due to transient overvoltages caused by restriking
ground faults. The remaining various grounding
methods can be applied on system grounding protection depending on technical and economic factors. The one advantage of an ungrounded system
that needs to be mentioned is that it generally can
continue to operate under a single line-to-ground
fault without an interruption of power to the loads.
(2) Solidly grounded system. A s o l i d l y
grounded system is one in which the neutral (or
occasionally one phase) is connected to ground without an intentional intervening impedance (fig 8-4).
On a solidly grounded system in contrast to an ungrounded system, a ground fault on one phase will
result in a large magnitude of ground current to
flow but there will be no increase in voltage on the
unfaulted phase. Solid grounding is commonly used
in low voltage distribution systems. Solid grounding
has the lowest initial cost of all Wounding methods.
It is usually recommended for overhead distribution
systems supplying transformers protected by primary fuses. However, it is not the preferred scheme
for most industrial and commercial systems, again
because of the severe damage potential of high magnitude ground fault currents. The NEC Article
250-5 (1990) requires that the following classes of
systems be solidly grounded:
(a) Where the system can be so grounded
that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts.
(b) Where the system is 3-phase, 4-wire,
wye-connected in which the neutral is used as a
circuit conductor.
(c) Where the system is 3-phase, 4-wire
delta-connected in which the midpoint of one phase
is used as a circuit conductor.
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
Figure 8-1. Typical Equipment Ground.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 8-2. Typical grounding system for a building and its apparatus.
(d) Where a grounded service conductor is
uninsulated in accordance with the NEC Exceptions
to Sections 230-22, 230-30 and 230-41.
(3) Resistance grounded system. Limiting the
available ground fault current by resistance
grounding (fig 6-5) is an excellent way to reduce
damage to equipment during ground fault conditions, and to eliminate personal hazards and electrical fire dangers. It also limits transient overvoltages
during ground fault conditions. The resistor can
limit the ground fault current to a desired level
based on relaying needs. At the occurrence of a
line-to-ground fault on a resistance grounded system, a voltage appears across the resistor which
nearly equals the normal line-to-neutral voltage of
the system. The resistor current is essentially equal
to the current in the fault. Therefore, the current is
practically equal to the line-to-neutral voltage di8-4
tided by the number of ohms of resistance used. The
grounding resistances are rated in terms of current
and its duration for different voltage classes.
(a) Low resistance grounding. Low resistance
grounding refers to a system in which the neutral is
grounded through a small resistance that limits
ground fault current magnitudes. The size of the
grounding resistor is selected to detect and clear the
faulted circuit. Low resistance grounding is not recommended on low-voltage systems. This is primarily because the limited available ground fault current is insufficient to positively operate series trip
units and fuses. These trip units and fuses would be
dependent upon both phase-to-phase and phase-toground fault protection on some or all of the distribution circuits. Low resistance grounding normally
limits the ground fault currents to approximately
100-600A. The amount of current necessary for se-
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 8-4. Methods of solidly grounding the neutral of three-phase systems.
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
lective relaying determines the value of resistance
to be used.
(b) High resistance grounding. High resistance grounding refers to a system in which the
neutral is grounded through a predominantly resistive impedance whose resistance is selected to allow
a ground fault current through the resistor equal to
or slightly more than the capacitive charging current of the system. Because grounding through a
high resistance entails having a physically large
resistance that is both bulky and costly, high resistance grounding is not practical and is not recommended. However, high resistance grounding
through a grounding transformer is cost effective
and accomplishes the same objective. High resistance grounding accomplishes the advantage of ungrounded and solidly grounded systems and eliminates the disadvantages. It limits transient
overvoltages resulting from a single phase-toground fault by limiting ground fault current to
approximately 8A This amount of ground fault current is not enough to activate series overcurrent
protective devices, hence no loss of power to downstream loads will occur during ground fault conditions. Special relaying must be used on a high resistance grounded system in order to sense that a
ground fault has occurred. The fault should then be
located and removed as soon as possible so that if
another ground fault occurs on either of the two
unfaulted phases, high magnitude ground fault currents and resulting equipment damage will not occur. High resistance grounding is normally applied
in situations where it is essential to prevent unplanned system power outages, or previously the
system has been operated ungrounded and no
ground relaying has been installed. Once the
ground point has been established through the resistor, it is easier to apply protective relays. The
user may decide to add a ground overcurrent relay
ANSI/IEEE device 50/51G. The relay maybe either
current actuated using a current transformer or
voltage actuated using a potential transformer. De-
pending on the priority of need, high resistance
grounding can be designed to alarm only or provide
direct tripping of generators off line in order to
prevent fault escalation prior to fault locating and
removal. High resistance grounding (arranged to
alarm only) has proven to be a viable grounding
mode for 600V systems with an inherent total system charging current to ground (31CO) of about
5.5A or less, resulting in a ground fault current of
about 8A or less. This, however, should not be construed to mean that ground faults of a magnitude
below this level will always allow the successful
location and isolation before escalation occurs.
Here, the quality and the responsiveness of the
plant operators to locate and isolate a ground fault
is of vital importance. To avoid high transient
overvoltages, suppress harmonics and allow adequate relaying, the grounding transformer and resistor combination is selected to allow current to
flow that equals or is greater than the capacitive
changing current.
d. Lightning grounds. Lightning grounds are designed to safely dissipate lightning strokes into the
earth. They are part of a lightning protection system which usually consists of air terminals (lightning rods), down conductors, arresters and other
connectors of fittings required for a complete system. A lightning protection system’s sole purpose is
to protect a building, its occupants and contents
from the thermal, mechanical and electrical effects
of lightning. Effective grounding for lightning
strokes is sometimes difficult to achieve because it
is nearly impossible to predict the maximum discharge current. Currents from direct strikes can
reach magnitudes of 100,000 amperes or more with
frequencies of tens to hundreds of kilohertz. Fortunately, the event is very short, thus allowing most
properly sized and maintained systems to survive
the "hit".
(1) Requirements. Main lightning protection requirement is dependent upon the height of the
building. According to NFPA 78-1986, there are two
classifications for a building. Class I is a building
with less than 75 feet height. The Class II building
is higher than 75 feet or has a steel frame with any
height. For further information about the lightning
protection code see NFPA 78-1986 which contains
more detail.
e. Electronic and computer grounds. Grounding
for all electronic systems, including computers and
computer networks, is a special case of the equipment ground and the system ground carefully applied. In fact, grounding systems for electronic
equipment are generally the same as for system
ground with an additional requirement: the degree
of performance required. Electronic equipment
grounding systems must not only provide a means
of stabilizing input power system voltage levels, but
also act as the zero voltage reference point. However, the need to do so is not restricted to a low
frequency of a few hundred hertz. Grounding systems for modem electronic installations must be
able to provide effective grounding and bonding
functions well into the high frequency megahertz
range. Effective grounding at 50-60 Hz may not be
effective at alI for frequencies above 100 kilohertz.
(1) Requirements. There are several aspects to
the requirement for good grounding performance for
electronic equipment; all of which are due to electrical circuit behavior. Digital systems operate at high
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
frequencies. Modem systems achieve clock and data
rates at 4 megahertz and higher. Clock rate is the
rate at which a word or characters of a word (bits)
are transferred from one internal computer element
to another. Data rate is the rate at which data is
transferred (bauds or bits per second) between computers. At these frequencies, due to the impedance,
a regular ground wire acts as conductor for only a
few feet. Compare the frequency and wavelength of
these systems with those used for 60 Hz power.
Electricity is conducted on a wire at very nearly the
speed of light (186,000 miles/sec.). Dividing the
speed by the frequency gives the full wavelength.
For 60 Hz, one wavelength is about 3,100 miles.
Communications and radar personnel know that interesting things begin to happen at one fourth of the
wavelength. The voltage and the current no longer
have the same relationship at this point on the wire.
The quarter wavelength for 60 Hz is about 775
miles. However, the quarter wavelength for ten
megahertz is only 24.5 feet. This is not the worst
case; the change in the current and voltage relationship along a wire occurs gradually over the distance
travelled. To maintain a close relationship between
the voltage and current at all points along the conductor’s path, it cannot be much longer than l/20th
of a wavelength. Therefore, effective ground conductor length for a ten megahertz signal is only about
4.9 feet. This does not mean electronic grounding
systems cannot be longer than four or five feet. The
important conductor is the equipment grounding
(bonding) conductor, which may be a copper cable,
strap, sheet, or braid. It is this particular conductor
which limits how far the electronic or computer
equipment may be placed from the signal reference
grid (equipotential plane) or system.
(2) Noise interference. Coupled and induced
electrical noise is also a problem at higher frequencies. This effect is rarely a concern for systems
operating at the 60 Hz powerline frequency. Very
little, if any, current is induced or coupled to the
ground conductors at low frequency. At high frequency, relatively more current is induced into the
ground conductors through shields, cable trays, conduit, and the enclosures used to house the electronic
system- As a result, these conductors must deal
with more noise current than 60 Hz systems. In
addition, they must hold the reference voltage very
near zero at all points on the equipotential system.
(3) Power system grounding. The input power
system ground resistance is important because it
keeps the system voltage at nominal values. This
“resistance” is not only a simple resistance measurement but also a frequency dependent impedance
measurement. The best test instruments (para
14-5) actually apply an alternating current which
returns a measurement of the conductors’ inductance plus the grounding system’s contact resistance. If the ground resistance reading is high at
the low frequencies applied by test instrument, it
will be much higher at the higher frequencies. The
manufacturers of some electronic systems call for
system grounding resistance of one ohm or less.
This low resistance is many times more difficult to
achieve than the 25 ohm maximum grounding resistance of a made electrode for power systems (NEC
article 250-84). To put that in perspective; aircraft
do not maintain an earth ground, but do maintain a
low impedance between on-board electronic devices
by using the aircraft skin and framework as a zero
voltage equipotential plane.
(4) Loop-flow. A low resistance to ground in the
input power system is no promise of trouble-free
performance. It is necessary to understand that the
earth is not a magic dumping area where unwanted
signals and currents simply disappear. Currents always flow in complete circuit loops that may include
various portions of the earth, the grounding electrodes, the grounding conductors, equipment bonds,
and the equipment enclosures.
(5) Isolated ground system. Loop currents flowing through one portion of the earth into another
usually include a substantial amount of induced
high frequency common mode noise. Many designers have tried to solve the noise problem with a
single point, isolated ground system. This system
uses an insulated ground wire from the load to the
service entrance panel board. All isolated ground
outlets are of a special design such that the ground
wire is isolated from the normal connections to the
metal mounting frame and electrical outlet box. The
isolated ground system is actually a very high impedance at high frequencies. This high impedance
does attenuate this noise, but causes problems as
high frequency voltages build up over its length,
due to the high frequency current through the impedance of the conductor (IZ). Most manufacturers
now include surge protection with their isolated
ground receptacles to protect the equipment from
the high voltages that develop at high frequencies
across these types of receptacles (common and
transverse mode). All exposed metal parts still require the equipment ground conductor. Therefore,
two ground conductors are required: the equipment
safety (“dirty”) ground, and the isolated system
(“clean”) ground. All of the equipment grounds are
routed and bonded in the normal way. All isolated
ground conductors must be brought back to one
point in the subpanel. The subpanel isolated ground
bus must not be bonded to the subpanel enclosure.
This ground bus must be isolated and only connected with insulated conductor(s) to the service
TM 5-683/NAVFAC M-116/AFJMAN 32-1083
entrance ground bus. The input power system neutral must also be grounded only at the service entrance. The isolated ground system stops loop currents and common mode electrical noise, but has
several major disadvantages: The long branch
feeder and isolated ground conductors are effective
only for low data transfer frequencies (fig 8-6c.
High voltages occur between the conductors during
surges. It is also a very difficult system to inspect
and maintain. Frequency inspections must be made
to ensure the system has not been defeated by inadvertent or deliberate installation of a jumper or
conductor between the two systems. Inspections
and tests on this type of grounding must be carried
out after each electrical system modification. It is
best not to use isolated ground systems at all unless
forced to by the equipment manufacturers. It is also
best to restrict such systems to small areas or only
one floor of the building.
(6) Electronic system grounding. Good electronic system grounding performance is achieved
with a properly laid out distribution of multipoint,
well-bonded grounding connections. This system
can use bare, braided, sheet, or stranded copper
conductors for grounding or bonding functions. This
system requires conduit and equipment enclosure
bonding at all junction points. In other words,
simple metallic contact between the enclosures, wiring conduits, and power panels is not enough. The
multipoint bonding provides low impedance grounding for the electronic equipment. The low impedance between the separate items of electronic equip
ment keeps the noise voltages at or near zero
between them and, therefore, provides an
“equipotential plane”. This system is much easier to
inspect and test. No special requirements must be
met during modifications or expansion of the electrical system. All power panels and all supply transformers feeding an installation with this type of
grounding system must be grouped and bonded together using short lengths of bare, braided, sheet, or
stranded copper conductors in order to achieve the
effective high frequency grounding performance described above. As shown in figure 8-6d, a single
area of power entry with a large equipotential
ground plane and short equipment grounding conductors forms the preferred grounding system for
large automated data processing (ADP) and computer applications.
f. Maintenance safety grounds. Grounds used for
maintenance work are usually intentional, but temporary, connections between equipment power conductors and ground. These connections are always
applied after the power source has been turned off
and the circuit(s) have been tested and are known to
be de-energized. The ground is intended to protect
maintenance personnel from an inadvertent reenergization of the circuit. The ground is removed
tier maintenance operations have been completed.
Application of a maintenance ground is discussed in
more detail in paragraph 12-2d.
g. Ground system tests. Periodic testing should be
done to assure grounding system effectiveness. The
following are points that should be addressed during inspection and maintenance:
(1) Inspect and test single point, isolated
ground systems after every electrical system modification. visually inspect outlets and panels for conductors forming loops between the equipment
ground and the isolated ground.
(2) Test the ground to neutral voltage at each
power distribution panel included in the particular
system. The voltage should be taken using a high
impedance AC voltmeter and an accurate record
should be kept. The voltage should be very low; on
the order of l0-150 millivolts (0.01-0.150V). Any
sudden changes or increasing trends should be investigated and the cause corrected.
(3) The made electrode, rod, plate, or selected
ground body contact point should be tested every
12-24 months. A record should be kept. Any increasing impedance indicates need for remedial action.
8-3. Ground fault interrupting methods.
Ground faults result when an electrical components
insulation deteriorates allowing an above normal
current leakage to ground. Minute current leakage
may normally occur from virtually every electrical
device. Ground faults become dangerous when an
unintended ground return path becomes established. This ground return path could be through
the normal electrical components and hardware
(equipment ground for instance), conductive material other than the system ground (metal, water,
plumbing, pipes, etc.), a person or, any combination
of the above. Ground fault leakage currents of much
lower levels than is needed to trip conventional circuit breakers can be hazardous. Therefore, to reduce the possibility of fire, injury, or fatality, the
NEC requires additional ground fault protection for
certain types of circuits. Ground fault protective
devices are of two distinct types: ground fault circuit interrupters and ground fault protectors. It is
extremely important to understand the difference
between them.
a. Ground fault circuit interrupters (GFI). A GFI
is designed to protect a person from electrocution
when contact between a live part of the protected
circuit and ground causes current to flow through a
person’s body. A GFI will disconnect the circuit
when a current equal to or higher than the calibration point (4 to 6 mA) flows from the protected
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 8-6. Grounding for Electronic and ADP Systems: a) Establish a central grounding point, b) Principal features of an isolated
grounding system.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Grounded by Gwen Wire Only
Figure 8-6. (Continued) Grounding for Electronic and ADP Systems: c) Avoid long runs of single grounding conductors, d) An effective
multi-point grounding system for high frequencies, e) Comparison of single conductors us a multi-point grid at high frequencies.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
circuit to ground (fig 8-6). It will not eliminate the
shock sensation since the normal perception level is
approximately 0.5 mA. It will not protect from electrocution upon line-to-line contact since the nature
of line-to-line loads cannot be distinguished by a
line-to-ground device. GFIs are sealed at the factory, and maintenance should be limited to that
recommended by the manufacturer. Tripping tests
should be performed with the test button on the
unit in accordance with the frequency recommended
by the manufacturer. Results and dates of tests
should be recorded on the test record label or card
supplied with each permanently installed GFI unit.
There are four types of GFIs. There are circuit
breaker type, receptacle type, portable type, and
permanently mounted type.
(1) Circuit breaker type. A circuit breaker type
GFI is designed in the form of a small circuit
breaker and is completely self-contained within the
unit housing. The circuit breaker type GFI provides
overload and short-circuit protection for the circuit
conductors in addition to ground-fault protection for
personnel. It is intended to be mounted in a
panelboard or other enclosure. For required maintenance refer to paragraph 5-4c.
(2) Receptable type. A receptacle type GFI is designed in the form of a standard receptacle that is
completely self-contained within the unit housing,
and does not provide overload or short-circuit protection. It is intended for permanent installation in conventional device outlet boxes or other suitable enclosures. Maintenance required for a GFI receptacle is
the same as any standard receptacle outlet. If the
GFI receptacle does not reset, is badly worn, cracked,
or broken, or if contacts are exposed, the GFI must be
replaced. It should also be replaced if accidental disengagement of a plug from the receptacle is a recurring problem. Proper wire connections on the receptacle and proper polarity of power connections should
be checked including the integrity of the equipment
ground. If there is abnormal heating on the GFI
receptacle face, check for loose terminal connections
and correct or replace. If there is evidence of burning
or arc-tracking, it should be replaced.
(3) Portable type. A portable type GFI is a unit
intended to be easily transported and plugged into
any grounded receptacle outlet. Cords, tools or other
devices to be provided with ground-fault protection
for personnel are then plugged into receptacles
mounted in the unit. Required maintenance would
include that recommended in paragraph (2) above
for receptacle type GFIs along with the following
cord care recommendations:
(a) Keep the cord free of oil, grease and other
material that may ruin the rubber cover. Avoid tangling knots or dragging across sharp surfaces.
(b) Make sure that the power tool is
grounded through the additional grounding conductor in the cord and the grounding prong of the plug.
The integrity of this ground circuit is necessary for
the Protection of personnel.
(c) Make sure that the cord is not cut, broken, spliced or frayed. Cords maybe replaced or the
damaged portion may be cut out and the two sections rejoined by attaching a plug and connector.
(d) Make sure that the green conductor is
connected to the frame of the tool and the grounding
prong of the attachment plug.
(4) Permanent type. A permanently mounted
type GFI is a self-contained, enclosed unit designed
to be wall or pole mounted and permanently wired
into the circuit to be protected. Maintenance beyond
tightening of connections and cleaning should not
be attempted. Any repairs needed should be referred to the manufacturer.
b. Ground fault protectors (GFP). A GFP is designed to limit damage to electrical equipment in
the event of a fault (either solid or arcing) between a
live part of the protected circuit and ground. A GFP
will cause the circuit to be disconnected when a
current equal to or higher than its setting flows to
ground (fig 8-7). GFPs are available with settings
typically ranging from five to 1200 amperes. It will
not protect personnel from electrocution. A GFP system is designed to be installed in a grounded distribution system. I t c o n s i s t s o f t h r e e m a i n
components: sensors; relay or control unit; and a
tripping means for the disconnect device controlling
the protected circuit. Detection of ground-fault current is done by either of two basic methods. With
one method, ground current is detected by sensing
current flow in the grounding conductor. With the
other method, all conductor currents are monitored
by either a single large sensor, or several smaller
ones. Sensors are generally a type of current transformer and are installed on the circuit conductors.
The relay or control unit maybe mounted remotely
from the sensors or maybe integral with the sensor
assembly. Circuit breakers with electronic trip units
may have a GFP system integral with the circuit
breaker. Any maintenance work performed on the
electronic circuitry should adhere to manufacturer’s
instructions. Maintenance on the mechanical operating mechanism components should be performed
as recommended in chapter 5. Maintenance requirements for the sensors are as specified in chapter 2
for instrument transformers. Tighten all terminal
connections and clean. Any repairs needed should
be performed by the manufacturer. If interconnections between components are disconnected, they
must be marked and replaced to maintain the
proper phasing and circuitry. If the system is
equipped with a test panel, a formal program of
periodic testing should be established. When the
system is not equipped with a test panel, refer to
the manufacturer for test instructions.
Figure 8-7. Ground fault circuit interrupter operation.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
9-1. Lighting maintenance.
Each lighting installation is designed to produce a
specific level of illumination adequate for those
working in the area. Adequate illumination should
be maintained to reduce eyestrain, improve morale,
increase safety, improve housekeeping, decrease fatigue, reduce headaches and increase production,
all of which are directly reflected in lower operating
cost. The maintenance of lighting systems is aimed
at preserving the light producing capability at the
original design level. Its necessity cannot be overemphasized. To prevent progressive deterioration of
the system, prompt repair of any deficiency is essential. Since dirt accumulating and lamp aging are the
two major factors which reduce the light output, it
is necessary that lamps, fixtures and reflective areas be kept clean; defective lamps be replaced; and
the voltage be held stable.
9-2. Fluorescent lighting.
There are three principal types of fluorescent fixtures; preheat, instant-start and rapid-start. All
have practically the same physical dimensions but
different internal construction. A preheat fixture
has a ballast and starter which supplies nominal
voltage to the lamp (fig 9-l). These are older style
fixtures which cause the fluorescent tube to flicker
before it lights. An instant-start fixture has a ballast which supplies a high voltage to the fluorescent
tube to light it instantly. A rapid-start fixture has a
ballast which requires a starting aid voltage between the full length of the lamp and the grounded
metal surface of the fluorescent fixture. The type of
circuit in which a particular lamp must be used is
etched on the end of the lamp. For most applications, the 4-foot rapid-start lamp is the preferred
lamp. Energy efficient lamps and electronic ballasts
are also available. They can replace standard fluorescent lamps and save electricity by providing fulllight output at reduced wattage and operating temperatures. Electronic ballasts can save up to 25
percent of the energy. The advantages of the electronic ballast besides energy saving, are lighter
weight, less humming noise, dimmable and capable
of operating up to four lamps at a time. The National Electrical Code Article 410-73 requires that
all indoor fluorescent fixtures (except those with
simple reactance ballasts) incorporate Class p ballasts with integral thermal protection. This requirement applies to all new installations and replace-
ments. Older models with simple (single winding)
reactance ballasts are an exception. The NEC Article 410-18(a) also requires that fluorescent fixtures as well as all other lighting fixtures and
equipment with exposed conductive parts be
grounded. Failure to properly ground the ballast
and fixture combination could result in shock hazard. In addition to a shock hazard, failure to properly ground a fixture may result in frequent tube
failures and trouble with starting for certain designs. For relamping or lighting retrofit it is important to assure existing ballast is in compliance with
the new lamp. For example, when replacing a T-12
with a T-8 lamp the new ballast for the T-8 should
be installed since the existing T-12 ballast is incompatible although the lamp bases are similar.
9-3. Incandescent lighting.
In an incandescent lamp, light is generated by heating the filament to incandescence. The hotter the
filament, the more efficient it is in converting electricity to light. However, when the filament operates hotter, its life is shortened. Therefore the design of each lamp is a balance between efficiency
and life. Incandescent lighting fixtures are designed
for a particular lamp size and type. However, it is
possible to use much higher wattage lamps in a
fixture than the fixture or the circuit can adequately handle. The excessive heat of higher wattage lamps can damage the sockets, increase failure
rates and overload the circuits. Personnel are cautioned to use only the lamp size (in watts) recommended for the fixture or smaller rather than a
higher wattage lamp that may physically fit. Incandescent lamps come in a variety of voltage ratings.
For most applications, the lamp voltage rating nearest the available line voltage should be selected.
Under this condition, the lamp will produce its
rated value of life, watts and light output. Energy
efficient replacements are available for standard incandescent lamps. They provide better lamp efficiency with no loss in lamp life. Many incandescent
lamps are available with life ratings in excess of
ordinary general service lamps. Some have ratings
of 5,000 hours or more and some even are guaranteed to burn for five years. Use of these lamps may
be practical at locations where access is limited including high ceiling auditoriums, exit lights, stairwells, and marker lights on towers or fire alarm
boxes. Use of an ordinary general service lamp
whose voltage rating is higher than the circuit volt9-1
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 9-1. Preheat fluorescent lamp and fixture components.
age may be another alternative for inaccessible locations. By operating the lamp below its rated voltage, the life is increased but the light output is
9-4. High intensity discharge lighting (HID).
High intensity discharge lamps are those which
have a gaseous discharge arc tube operating at
pressures and current densities sufficient to generate desired quantities of visible radiation within
their arcs alone. Every HID light source-mercury,
metal halide, or high or low pressure sodium requires a ballast. Without a ballast, the lamp will not
work; the arc will act as a short circuit and the lamp
will destroy itself. Not only is a ballast necessary for
lamp operation, but a properly matched ballast is
essential to achieve rated life and performance with
any HID lamp. Therefore, all ballasts should be
designed to match the supply voltage with lamp
requirements, to start the lamp and to control its
performance throughout its life according to data
published by the lamp manufacturer. Ballast designs differ widely between mercury, metal halide,
HPS and LPS light sources and are therefore not
a. Mercury lamps. The maintained light output of
mercury lamps is high because the electrodes operate at a relatively cool temperature resulting in less
oxide contamination of the operating electrodes and
the discharge gas. Long average life (24,000 hours or
more) is a primary characteristic of most mercury
lamps. While some models may have lamp bases the
same size as incandescent lamps, standard mercury
lamps must never be used to replace a burned out
incandescent lamp (fig 9-2). However, there are selfballasted mercury lamps which can be used as direct
replacements for incandescent lamps. The installer
should check which type is compatible with the fixture before turning on the power. An objectionable
characteristic of mercury lamps is the time required
to reignite (several minutes) after a momentary loss
of power. It should be noted that this lamp can cause
serious skin burn or eye inflammation from ultraviolet radiation if the outer envelope of the lamp is
broken or punctured, and the arc tube continues to
operate. Lamps allowed to operate in this way constitute both a fire and a personnel safety hazard and
should be replaced promptly. There are certain
lamps available that will automatically extinguish
when the outer envelope is broken.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 9-2. Mercury lamp.
b. Metal halide lamps. Metal halide lamps resemble mercury lamps in appearance and are used
similarly. The color produced is better than mercury
lamps and control of the light is easier. The initial
efficiency is also better for wattages above 150W.
Otherwise mercury lighting is more efficient. Disadvantages of metal halide lamps are a higher cost,
and a shorter life expectancy than mercury lamps.
c. High pressure sodium (HPS) lamps. The HPS
lamp package is similar to the mercury vapor lamp.
Like most discharge lamps, the operating voltage is
not compatible with supply voltage and a current
limiting ballast must be used. The HPS ballast
must compensate for both variations in line voltage
and lamp voltage change due to ageing process in
the tube. The mercury lamp operating voltage
changes very little with life. With the HPS lamp,
the ballast must compensate for changes in the
lamp voltage as well as for changes in the line
voltage. The operating voltage of an HPS lamp can
change as much as 60 percent as it ages and the
ballast operating characteristics throughout the life
of the lamp is the key to good system performance.
High pressure sodium. is more efficient than mercury or metal halide lamps.
d. Low pressure sodium (LPS) lamps. The LPS
lamps are physically and electrically similar to fluo
rescent lamps but without the phosphor coating. A
ballast is required to start the LPS lamp. There is
about a 10-minute warm-up period when the lamp
is first turned on. LPS lamps are larger than mercury, metal halide and HPS lamps. The largest LPS
lamp is 180 watts, 44 inches long and emits 33,000
lumens of yellow (monochromatic) light compared to
a 400-watt HPS lamp 10 inches long which emits
50,000 lumens. There are about 1000 milligrams of
sodium in the 180-watt LPS lamp compared to 6
milligrams of sodium in the 400-watt HPS lamp.
Because of this, LPS lamps require special disposal
precautions that do not apply to HPS lamps. Applications for LPS lamps are limited to roadways or
floodlighting where color rendition is not important.
(1) Installation. A suitable ballast must be used.
The ballast must be in compliance with Illuminating
Engineer Society (IES) and/or ANSI specifications- If
using power factor correction in a star connected
multi-phase distribution, the power factor correcting
capacitor should be connected between the line and
neutral. A filter coil must be used if there is audiofrequency switching signals on the mains. The lamp
should be installed within the indicated limits to
avoid accumulation of sodium in the arc tube. Accumulation of sodium could reduce lamp life. Lamps of
90 watts or more must be set within 20 degrees of
horizontal. Lamps of 55 watts or less may operate up
to 20 degrees above horizontal.
(2) Maintenance. Do not allow the lamp to be
scratched. Ensure that power is off before installing
or removing the bulb. To avoid electric shock do not
touch any metal parts of a broken bulb. A great
degree of heat is produced by contact of the sodium
with a small amount of water. Therefore the lamps
must be stored or carried in their original container.
(3) Disposal. Let the lamp cool before removal.
To avoid the danger of fire or broken glass, care
must be taken in handling discarded lamps. No
more than 20 lamps at one time should be broken
into small pieces in a dry container of adequate size
and in an open area. To avoid injury from flying
glass, goggles should be worn. The broken pieces
should be sprayed with water from a distance.
When the chemical reaction has ceased the sodium
is harmless and the broken glass should be disposed
of as normal waste.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
9-5. Cleaning.
The cleaning schedule should be coupled with
relamping (spot/group schedule to minimize labor
costs). The cost of cleaning versus replacement
should be carefully evaluated. It is well-known that
dirt absorbs and masks light. The progressive decrease of light caused by accumulating dirt renders
periodic cleaning of lighting equipment-lamps, reflectors and lens--a necessity. The frequency of
cleaning depends entirely upon local conditions.
Fixtures in air-conditioned and air-filtered rooms
may require cleaning only once a year. But in an
atmosphere which is heavy with dust and fumes,
cleaning every few weeks may be necessary. The
cleaning intervals for a particular installation
should be determined by light meter readings after
the initial cleaning. When subsequent foot-candle
readings have dropped 15-20 percent, the fixtures
should be cleaned again. Readings should be made
with the light meter at the working surface with the
meter reader in the position of the operator or person using the working surface. Lighting equipment
should be washed, not just wiped with a dry cloth.
Washing reclaims five to ten percent more light
then dry wiping and reduces the possibility of marring or scratching the reflecting surfaces of the fixtures. Glassware, reflectors and diffusing louvers
that can be removed should be cleaned as follows:
a. Immerse in the washing solution. Do not immerse lamp base or electrical connections in the
cleaning solution. Scrub with a soft brush or sponge.
When incrustation is not removed by scrubbing, use
No. 0 steel wool to remove dirt film.
b. Rinse in warm clear water and dry with a
clean cloth. Walls, ceilings and surroundings are an
important part of the overall illumination system
since they redirect light to the working area. The
most efficient lighting system is obtained when the
fixtures are new and when the walls, ceilings, floors
and furnishings of the room are clean and colored
with a high reflectance color. A lighting maintenance program must therefore include cleaning and
painting of the walls and ceilings in addition to the
fixture cleaning schedule. Glassware, reflectors and
diffusing louvers that cannot be removed should be
cleaned as follows:
(1) Wipe with a moist cloth or sponge. When
incrustation is not removed by sponging, use No. 0
steel wool to remove dirt film. Care should be taken
to ensure that shreds of steel wool do not touch the
pin contacts or get into the lamp socket.
(2) Wipe off excess moisture with a clean cloth.
Clean fixture holders and stem hangers with a
moist sponge or cloth and wipe dry. Enameled,
chrome, aluminum or silver-plated reflecting sur9-4
faces that cannot be adequately cleaned and polished should be replaced.
9-6. Relamping.
The longer a lamp remains in service, the less light
it produces. The different types of lamps-filament,
fluorescent or high intensity discharge-depreciate
at different rates. Since their life expectancy is also
different, replacement intervals will vary. The two
general relamping procedures are spot relamping
and group relamping.
a. Spot relamping. Spot relamping is the replacement of individual lamps as they fail. Lamps that
are blackened or discolored should also be replaced
even if they are still burning because this discoloration indicates that the lamp will soon fail. Fluorescent lamps should be replaced as soon as they begin
to flicker, or when the ends of the tube adjacent to
the base blacken (fig 9-3).
b. Group relamping. Group relamping is most applicable to fluorescent lighting. When relamping, it is
economical to wash the fixtures. It is also advantageous to inspect the sockets, hangers, reflectors and
lens for broken glass, loose mountings, etc. Refer to
the lamp manufacturer for recommended replacement intervals and relamping procedures. It should
also be noted that replacement lamps must be of the
same type, color, wattage and voltage as those being
replaced. The following procedures apply:
Figure 9-3. Trouble-Shooting Fluorescent Lighting: a) Grey or
brown bands 1“—2” from base are normal and do not affect useful
life, b) Dark spots caused by condensed Mercury. Usually disappear after lamp warms up, c) Large blackened areas at ends mean
lamp is at end of useful life.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(1) Plan to replace all fluorescent lamps in a
given area upon completion of 80 percent of rated
burning life. Keep records of dates, costs, and other
pertinent information as necessary to determine the
realized savings.
(2) While the existing lamps are lighted, pick
the best 20 percent of old lamps and save for replacement stock. Choose only the brightest and cleanest
lamps for this purpose. Discard the remainder. Install new lamps in all sockets. Use the replacement
stack to replace the first 20 percent of individual
lamps as they burn out. When all of the replacement
lamps have been used, make another complete replacement of lamps and repeat the process.
9-7. Lamp trouble-shooting.
Light sources operate most efficiently and economically at their rated voltages. Operation outside their
normal operating range is undesirable. Both
undervoltage and overvoltage conditions have detrimental effects on the life, efficiency, and economy of
the light sources. These effects are as follows:
a. For fluorescent lamps, line voltage greater
than the maximum ballast range will shorten lamp
and ballast life. Line voltage less than the minimum
ballast range will also shorten lamp life, reduce
illumination and may cause uncertain starting. Frequent starting will shorten lamp life.
b. For incandescent lamps, line voltage greater
than the maximum lamp range will increase the
light output but will shorten the lamp life. Line
voltage less than the minimum lamp range will
extend lamp life but will reduce light output by
approximately three percent for each one percent
drop in voltage.
c. For HID lamps, line voltage greater than the
maximum ballast range will shorten lamp and ballast life. Line voltage less than the minimum ballast
range will reduce light output and may cause uncertain starting.
d. With the more common lamps and circuits,
continuous flashing or blinking will destroy the
starter, shorten lamp life and possibly damage
the ballast. Whenever possible, replacement ballasts should be of the “P’’-rated type that have
internal temperature sensitive overload protection. This is not always possible as “P” ballasts
may not operate satisfactorily in equipment that
is otherwise satisfactory. Original type ballasts
should be used if available. Replacement ballasts
should be of the type having an overload circuit
opening device. Other more common troubles encountered with lamp equipment, the probable
causes and the suggested solutions are listed in
table 9-1.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 9-1. Lamp Trouble-Shooting Guide.
Fluorescent Lamp Equipment
Lamp pins not
Seat lamp firmly and
Starter defective
Replace with tested
Low line voltage
Match lamp rating to
line voltage or
increase line voltage
Fault in circuit of
Check wiring and lamp
holders. Check
Low temperature of
surrounding air
Shield lamp from
drafts. Enclose lamp
to conserve heat.
Maintain voltages
within the rated
voltage range of the
lamp. Use thermaltype starters.
Poor ground on rapid
start ballast
Ground the fixture
Lamp at end of life
Replace with tested
Lamp flickers,
swirls, or
Cold or too rapid
Allow a new lamp to
operate a few hours
for seasoning. Turn
off a few moments then turn on. Change
lamps and, if flicker
remains, replace
End of map glow
Poor ballast
Check ballast
Faulty starter
Replace starter
Improper wiring or
Check wiring and
ballast for ground
Improper starting
Replace starter
Low line voltage
Increase voltage
Poor lampholder contact
Seat lamp firmly in
Check ballast and
Lamp fails to start
or flashes on and
off .
Lamp darkens early
in life
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 9-1. Lamp Trouble-Shooting Guide-Continued.
Fluorescent Lamp Equipment
Short lamp life
Radio interference
Noise from ballast
Low or high line
Maintain branch circuit
voltage within the
range specified on
Lamp turned on and off
Frequency of starting
affects lamp life.
Long periods of burning
give long life. Short
periods of burning
reduce lamp life
Not installed properly
Auxiliary equipment
should be enclosed in a
steel channel. Wiring
should be made up with
tight connection;
clamps and starters
should be firmly
installed in sockets
and fixture grounded
Line feedback
Install filter at radio
Radiation direct from
Locate radio antenna
system at least 10 ft.
from fixtures
Fluorescent equipment
is not noiseless type
If unit is particularly
noisy, replace
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 9-1. Lamp Trouble-Shooting --con tinued.
Lamp fai1s to
Lamp frequently
goes out
Lamp loose
Tighten in socket
Low voltage
Increase lamp voltage
by changing transformer
Wiring fault
Check wiring.
Low temperature
Lamps may not start
when temperature is
below 32° F
Fluctuating voltage
Check line voltage.
(Momentary dips of 10
percent, or more, often
cause lights to go
Lamp burned out
Wiring fault
Tighten connections.
Check wiring. Separate
lighting circuits from
heavy power circuits
Cyclic flicker
Where there is a 3phase supply, connect
luminaries on
alternate phases. On
single phase, add
incandescent luminaries
to the system
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 9-1. Lamp Trouble-Shooting Guide-Continued.
Lamp loose
Tighten in socket
Loose or broken
Secure terminals.
Repair wiring
Lamp burned out
Replace with new lamp
Lamp burns dimly
Low voltage
Match lamp rating to
line voltage or
increase line voltage
Short lamp life
High voltage
Match lamp rating to
line voltage.
Improve voltage
regulation and avoid
Lamp failure due to
mechanical shock
Replace lamp. Be sure
water does not drip on
bulb. Use rough
service lamps if
Incorrect lamp
Replace with lamp of
size for which
luminaire is rated
Excessive vibration
Use vibration or rough
service lamps
Water contacts bulb
Use enclosed vaportight luminaire if
exposed to moisture
Bulb touches luminaire
Use correct lamp size
Lamp not burning
Lamp breakage
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
10-1. Other systems.
Previous chapters have outlined methods for servicing electrical system components such as switchgear, transformers, rotating equipment, etc. These
are the major areas in which real property electrical
shops are involved. There are, however, many other
interior systems which merit some mention. Detailed operation and maintenance data on these systems are difficult to develop due to the wide variety
of types of interior systems and the uniqueness of
each system. It is, therefore, suggested that all
manufacturer’s publications for a particular system
be obtained and all recommended maintenance and
troubleshooting practices be followed.
10-2. Emergency and stand-by systems.
The function of an emergency power system is to
provide a source of electrical power of required capacity reliability, and quality for a given length of
time to loads within a specified time after loss or
failure of the normal supply. The continued reliability and integrity of this power system is dependent
upon an established program of routine maintenance and operational testing. This program shall
be based upon manufacturer’s recommendations,
instruction books, and the minimum requirements
presented in this section. Instruction books protided by the manufacturer shall contain: a detailed
explanation of the operation of the system; instructions for routine maintenance; detailed instructions
for repair of the components of the system; pictorial
parts list and part numbers; and, pictorial and schematic electrical drawings of wiring systems, including operating and safety devices, control panels,
instrumentation and annunciators.
a. Special tools and testing devices required for
routine maintenance shall be available for use when
needed. Spare parts shall be stocked as recommended by the manufacturer. A written record of
inspections, tests, exercising, operation, and repair
of an emergency power system shall be maintained
on the premise. This record shall include: date of
the maintenance report; identification of the servicing personnel; and, notification of any unsatisfactory conditions and corrective actions taken, including parts replacement.
b. Transfer switches shall be subjected to a
maintenance program to include tightening connections, inspection or testing for evidence of overheating and excessive contact erosion, removal of dust
and dirt, and replacement of contacts as required.
As a minimum, a monthly load test of thirty minute
duration shall be conducted on an emergency power
system. Backup power should be tested at full critical emergency load. If it is impossible to test at full
load, then the test load capacity shall not be less
than 50 percent of the total connected critical emergency load. The test should include a complete cold
start of the generator. Consideration should also be
given to more stringent conditions as recommended
by the individual energy converter manufacturer. At
the time of emergency power system load testing,
all transfer switches and emergency system circuit
breakers shall be exercised. The routine maintenance and operational testing program shall be
overseen by a properly instructed individual.
10-3. Signal systems.
Signal systems include nurses’ call systems, paging
systems, buzzers, intercommunication sets and
similar devices. For the most part, these do not
require servicing at regular intervals. Generally, it
is sufficient to clean the equipment occasionally and
perform repair after some trouble is indicated. Local
evaluation will be used in determining servicing
10-4. Detection systems.
There are many types of intrusion and fire detection
systems in use at military installations. All require
frequent tests and checks, in some instances as often as once a day. The emphasis is on operational
tests to ensure the continued functionability of the
designed system, rather than on routine maintenance of component parts. Spare parts such as relays, contacts, batteries, transistors, pilot lamps
and detectors should be stocked for fast replacement. Further information is available from publications listed in appendix A. In all cases, the manufacturer’s instructions should be carefulIy followed.
Detection alarm systems are generally composed of
very rugged and reliable components. Little repair
work is required other then replacement of expendable parts and maintenance generally involves the
cleaning of alarm system sensors, such as smoke
detectors. Because most systems appear complicated and highly sophisticated at first, the tendency
is to turn over the maintenance to a service company. In actuality, the systems are much less complicated and most electrical servicemen can master
the work with brief training. Electrical shops nor10-1
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
really have all the tools and test equipment needed
to service these alarm systems. Consequently, the
cost will be much less if the routine maintenance is
performed in-house.
a. Fire detection system. The concept of defense in
depth is applied in fire protection when an early
warning fire detection system is used to communicate plant or equipment status to a central location
or assigned staff. The first line of defense is the
early warning fire detection system designed to detect the particles of combustion formed before overt
signs of fire appear, followed by systems designed to
detect fire and release extinguishing agents. The
system’s purpose is to provide the earliest possible
warning of a potential fire hazard, principally by
the extensive use of ionization smoke detections. One
of the major advantages of using a remote multiplexing system for fire detection is the ease of adding alarm detectors without the requirement of long
conduit and multiple cable runs throughout the
plant. A sample arrangement of this type of system
is as shown in figure 10-1. The early warning fire
detection system may be a Class A proprietary protective signaling system that meets the requirements of The National Fire Protection Association
(NFPA) Standard for the Installation, Maintenance,
and Use of Protective Signaling Systems (NFPA 7290). Class A and Class B fire detection circuits are
shown in figure 10-2. Class A means a fire alarm
can be received and displayed at the central alarm
station in the abnormal presence of a single break of
a single ground fault in any signaling circuit. A
Class B system does not include this emergency
operating feature. NFPA 72-90 also deals with the
styles of supervisory circuits. NFPA 72-90 further
requires that the central alarm station be continuously manned. Alternative main power supply
sources must be provided within the supervisory
central station. The signal-initiating device in the
fire detection system is the fire detector. The three
basic types of detectors can detect smoke, heat, and
flame. In addition to these generic types, detectors
can be configure as spot type or line type (table
10-1). In spop-type detectors, such as smoke detectors, the sensing element is concentrated at a particular location. Line-type detectors sense temperature changes along the length of a metal wire. When
heat above a predetermined level reaches the lines
strung throughout an area to be protected, an alarm
or alarm and fire-suppression system is triggered.
Heat detectors are fixed-temperature, rate-compensated, or rate-of-rise types. A fixed-temperature detector is a device that responds when its operating
element becomes heated to a predetermined level or
higher. A rate-compensated detector is a device that
responds when the temperature of the air surrounding the device reaches a predetermined level, regardless of the rate of temperature rise. A rate-ofrise detector is a device that responds when the
temperature rises at a rate exceeding a predetermined amount.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(1) Smoke detectors. Two types of smoke detectors are used: ionization and photoelectric. Ionization smoke detectors contain a small amount of radioactive material which ionizes the air in the
sensing chamber, thus rendering it conductive and
permitting a current flow through the air between
two charged electrodes. When smoke particles enter
the ionization area, the detector circuit responds
with an alarm or buzzing.
(a) Photoelectric spot-type detectors contain
a chamber that has either overlapping or porous
covers of light that allows the entry of smoke. The
unit contains a light source and a special photosensitive cell in the darkened chamber. The cell is either
placed in the darkened chamber at an angle different from the light path or has the light blocked from
it by a light stop or shield placed between the light
source and the cell. With the admission of smoke
particles, light strikes the particles and is scattered
and reflected into the photosensitive cell. This
causes the photosensing circuit to respond to the
presence of smoke particles in the smoke chamber.
(b) Flame detector is a device that responds
to the appearance of radiant energy visible to the
human eye or to radiant energy outside the range of
human vision.
(c) Photoelectric flame detector is a device
which the sensing element is a photocell that either
changes its electrical conductivity or produces an
electrical potential when exposed to radiant energy.
(d) Flame flicker detector is a photoelectric
flame detector with means to prevent response to
visible light unless the observed light is modulated
at a frequency characteristic of the flicker of a
(e) Infrared detector is a device with a sensing element which is responsive to radiant energy
outside the range of human vision.
(f) Ultraviolet detector is a device with a
sensing element which is responsive to radiant energy outside the range of human vision.
(2) Sprinkler systems. Protecting the plant
from fire frequently requires the installation of a
sprinkler system. Equipment consisting of overhead
piping and attached sprinklers connected to an automatic water supply protects defined spaces and a
variety of hazards. There are four major types ‘of
sprinkler systems: The wet-pipe system is the simplest and most common. The piping is always filled
with water, which begins to flow as soon as the first
sprinkler opens. Other types are dry-pipe, deluge,
and pre-action systems.
b. Security system. Before the advent of low-cost
computer multiplexed hardware, security systems
were simple hardwired alarm systems, providing a
minimum level of intrusion detection. Today, the
system may be a fully redundant computer-based
system interfaced with a redundant looped timedivision-multiplexed communication network for
gathering alarm data from sensors and for sending
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
commands to release locked doors under the cardaccess control subsystem. The remote multiplexer
may be microprocessor-based units, capable of data
collection, communication with the host computer,
and performing limited-access control functions.
The security system provides location information
as well as delay time for the guards. By successive
detections, the security force can track the intruder
and relay location information via portable radio
communications equipment to the responding
guards. In turn, the guards can constantly inform
the security force on the progress of their work or
the need for additional assistance. The cameras,
using various means of target intensification, can
“see” better than the human eye. Guard patrols are
also used to detect unusual activity. Perimeter detection is accomplished by the application of electronic detection systems.
(1) Microwave detection links. These devices
are mounted on posts inside the fence. Transmitters
radiate amplitude modulated X-band energy and
receivers detect and process the received energy.
Thus, an invisible energy envelope is produced that
will detect an intruder.
(2) Infrared detection links. These devices are
postlike and mounted inside the fence. Transmitters
radiate multiple beams of modulated infrared energy, and the receivers detect and process the energy. Penetration of the invisible infrared shield will
alarm the system.
(3) E-field links. Transmitter wires and receiver wires are strung horizontally from mounting
posts located inside the fence or mounted on the
fence. A radio-frequency energy field is generated
around the wires. The intrusion of a person into the
invisible field will “short” energy, creating an alarm.
(4) Buried sensor links. Devices sensing seismic, pressure, (or electromagnetic disturbances for
a combination of these) are buried inside the fence
and alarm upon the intrusion of someone into the
field of detection.
(5) Other systems. Other systems are available
that can be used in combination with the previously
mentioned systems. The probability of detection by
these outdoor devices depends on their application.
Perimeter detection equipment must be applied
with consideration of the environmental limitations
of the device’s technology. Once the intruder has
penetrated the fence, he has entered what is called
the protected area. Once again, visual or closedcircuit television surveillance may detect the intruder. Entry into a building is provided by the
application of a balanced magnetic switch on doors
and openings. This device uses an internal bias
magnet to balance a delicate reed switch in the field
of the external magnet attached to the door. Should
the door be opened, even a fraction of an inch, or
should another magnet be introduced in an attempt
to defeat it, the switch will change state and alarm.
Other devices for detection of an intruder may be
applied inside the building, including microwave
and infrared motion detection, photoelectric or laser
beams, seismic, sound detection, passive infrared,
and other devices. Because all the doors are locked
and alarmed, a means of allowing personnel to enter and leave must be provided. Positive-access control is established at the main guardhouse located
at the perimeter fence. All persons with a need to
enter the protected area are screened by explosive
detectors, metal detectors, and package X-ray detection equipment. Once permitted access to the plant
protected area, they are only allowed into vital areas within the plant on a need-to-enter basis. Control of personnel movement into vital areas is by
closed-circuit television/electronic-access control
equipment. At each vital area door, split image
closed-circuit television devices check the person
against his picture identification card. He then inserts his coded card into a magnetic reader, which
sends the coded information to the access computer.
If the person has been authorized to enter the particular vital area of the plant at that particular
time, the computer verifies the code and allows access. The guard watches the entrance via wideangle closed-circuit television to ensure that the
person enters alone. Using state-of-the-art circuit
design and multiplexing communication techniques,
the alarm monitoring systems offer a high degree of
tamper resistance. Redundancy is achieved by using
a central alarm station and a separately located
secondary alarm station. Electronic line supervision
or digitally encoded transmissions are used to prevent unauthorized persons from touching the system wiring. Any tampering will cause an alarm.
Access control, tamper indication, and administrative controls combine to prevent an insider from
attempting to sabotage the plant or help an outsider
penetrate the security system.
10-5. Monitoring systems.
Supervising the operations of the environmental
conditions throughout a building can be achieved by
the use of an integrated monitoring system. This
system consists of a centrally located console capable of continually monitoring many activities.
Console input signals may be initiated by pressure,
temperature, speed, humidity, air flow, electric current, water, steam, sewage, or opening or closing of
electric contacts. With this system, an operator can
quickly determine the operating condition of any
number of sewage lift stations, air conditioning
equipment, boiler auxiliaries or any other measur10-5
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
able condition or situation. Malfunctions are pinpointed in moments. The necessity for making daily
field checks is reduced or eliminated. Monitoring
systems consist of transducers located at the monitored equipment which convert some action into a
signal which, in turn, is transmitted to the console
by pneumatic, electrical or electronic means. Detailed plans, instruction books and maintenance
manuals on such systems should be obtained. Build-
ing personnel, whenever possible, should survey the
installation of the system and be able to locate components and determine operational methods. Most
monitoring systems contain solid-state devices
which are very reliable, but still require annual
servicing to ensure that all parts are functioning
properly (see chap 7). If skilled in-house personnel
are not available, local service contracts should be
used to accomplish servicing.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
11-1. Environmental protection.
This chapter concentrates on the Environment
Protection Agency (EPA) identification of hazardous substances. If a hazardous substance is released into the environment in a reportable quantity the facility Hazardous Waste Coordinator
must be notified. “Release” by definition involves
any spilling, leaking, pumping, emitting, empty.
ing, discharging, injecting, escaping, dumping or
disposing of a hazardous substance. A “reportable
quantity’’ varies by weight for each hazardous sub
stance. Refer to Section 311 of the Clean Water Act
(CWA) for established quantities for hazardous
substances. For hazardous substances not listed,
one (1) pound or more of that substance released
to the environment is reportable until otherwise
specified by the EPA. Failure to comply with notification requirements may result in civil and
criminal penalties. In all cases, handling and disposing of any hazardous substance must be directed by the Site Hazardous Waste Coordinator.
Hazardous substances include:
a. Wastes listed in the Resource Conservation and
Recovery Act (RCRA).
b. Air pollutants listed in the Clean Air Act
(CAA)-Section 112.
c. Substances and priority pollutants listed in the
Clean Water Act (CWA)-Sections 311 and 307a.
d. Chemical substances designated under the
Toxic Substances Control Act (TSCA)-Section 7.
e. Other substances as designated by the EPA
11-2. Polychlorinated biphenyls (PCBS).
PCBs belong to a broad family of organic chemicals known as chlorinated hydrocarbons. Virtually
all PCBs have been synthetically manufactured.
Their use has primarily been in transformers and
capacitors but they are also found in fluorescent
ballasts. PCBs are no longer intentionally manufactured in the United States although inadvertent production of PCB byproducts can occur when
chlorine, organic carbon, elevated temperatures or
catalysts are present together in a process. The
Monsanto Corporation was the principal domestic
manufacturer of PCBsand marketed the product
under the trade name, Aroclor. However, other
companies who used PCBs in the manufacture of
transformers, capacitors, etc. used other trade
names (table 11-1). From an electrical standpoint,
one desirable feature of PCB is its chemical stabil-
ity. Resistance to degradation by heat, oxidation
etc. is very desirable. But it is the long life feature,
coupled with the fact that PCB is bioaccumulative
and concentrates in the fat tissue of fish and other
animals, including man, that has led to its identification as an environmental problem. Handling,
storage and disposal of PCBs and products containing PCBs are therefore regulated by the EPA
and the Site Hazardous Waste Coordinator. All
questions pertaining to hazardous wastes should
be directed to that office. Basic concepts have been
presented to acquaint facilities personnel with the
hazards of PCBs. Physical problems which maybe
related to PCB exposure include an acne-like skin
eruption associated with baking, soldering or heat
transfer applications; changes in skin pigmentation; peripheral numbness; digestive upsets; headaches; and fatigue. PCB has also been found by
the Occupational Safety and Health Administration (OSHA) to include tumors in experimental
animals after repeated oral ingestion and concludes that PCBs are a potential carcinogen to
humans. Unless laboratory tests confirm the presence of less than 50 parts per million (PPM) of
PCB, then all transformers or capacitors filled
with petroleum-based dielectric are assumed to be
PCB-contaminated for EPA regulatory purposes.
Sample testing an oil sample involves a comprehensive test, a gas-in-oil test and a presence of
PCBstest. The gas-in-oil analysis determined the
concentrations of gases absorbed in the oil sample.
The presence of PCBs analysis determines the
concentration of PCBs in the oil sample. Oil classifications and concentrations are: non-PCB—less
than 50 PPM; PCB contaminated-greater then
50 PPM but less than 500 PPM and, PCB-greater
than 500 PPM. The comprehensive test includes
the following analyses:
a. Dielectric strength.
b. Color.
c. Acidity.
d. Water content.
e. Viscosity.
f. Specific gravity.
g. Pour point.
h. Interracial tension.
i. Power factor.
j. Corrosive sulphur.
k. Visual examination.
l. Particle count.
TM 5-683/NAVFAC MO- 116/AFJMAN 32-1083
Table 11-1. Common trade names for PCBs by manufacturers.
American Corp.
Allis Chalmers
Sangamo Electric
Cornell Dubilier
McGraw Edison
Westinghouse Electric
Wagner Electric
General Electric
Kuhlman Electric
Bayer (Germany)
Caffaro (Italy)
Caffaro (Italy)
Mitsubishi (Japan)
Prodelec (France)
Prodelec (France)
Mitsubishi (Japan)
Note. Generic Trade name use for non-flammable insulating liquids containing PCBs in capacitors and transformers.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
11-3. Lighting ballast.
Since the capacitor of the ballast in fluorescent lamps
contains a small quantity of PCB the EPA has laid
out regulations for the disposal of lighting ballast:
a. If the PCB lighting ballast is leaking the disposal is regulated under the Toxic Substance Control Act (TSCA). The leaking ballast must be incinerated at an EPA approved incinerator.
b. If the PCB lighting ballast is not leaking the
disposal is not under the TSCA. Check with your
local EPA office to find out any requirements in your
area for the disposal.
11-4. Flammable liquids and gases.
Flammability is the capability of a substance to
ignite easily, burn intensely and spread rapidly. Extreme caution should be taken when storing and
handling flammable materials, follow the National
Fire Protection Association (NFPA) Standard 251.
Of the flammable and combustible liquids and gases
in use, the most common are liquid hydrogen, liquified petroleum gas and natural gas (methane).
a. Hydrogen. Liquid hydrogen, like other cryogenic liquids, presents a hazard due to its extremely
low temperature, and the high pressures that can
be generated if it is allowed to evaporate in a confined space. However, the major hazard lies primarily in the wide ranges of flammability and detonability of gaseous hydrogen in air. The principal
method of preventing hydrogen gas ignition or detonation is by diluting the gas below the lower limit of
flammability and eliminating all sources of ignition.
This can be accomplished by:
(1) Providing adequate ventilation.
(2) Avoiding areas where pocketing may occur.
(3) Minimizing confinement.
(4) Limiting the amount of liquid hydrogen at
any one location.
(5) Using non-sparking tools and explosionproof equipment.
(6) Grounding equipment properly.
(7) Avoiding open flames.
(8) Observing no-smoking rules.
b. Liquified petroleum gas (LPG). LPG is a dangerous fire and explosion hazard when released in
air. Vapors may flow along surfaces for substantial
distances, reach a source of ignition and flash back.
LPG is also an asphyxiant. It is heavier than air,
and may accumulate in pits and other low lying
areas where it may displace air. Contact with liquified gas can cause frostbite. The following special
precautions must be observed:
(1) LPG must be stored and used in wel]ventilated areas, and kept away from heat, ignition
sources, and oxygen and chlorine cylinders.
(2) LPG systems shall have approved containers, valves, connectors, manifold valve assemblies
and regulators.
(3) LPG systems shall meet all Department of
Transportation specifications.
(4) LPG containers and vaporizers shall have
at least one approved safety relief valve.
(5) LPG shall not be stored within buildings.
(6) LPG storage locations shall be equipped
with at least one 20-B/C rated fire extinguisher.
c. Natural gas (methane). Under normal storage
and handling conditions, natural gas is stable when
contained. But when mixed with air or other oxidizing agents, it readily becomes flammable or explosive. Natural gas is lighter than air and can be an
asphyxiant by displacing air. The following precautions must be observed.
(1) Cylinders must be stored in well ventilated
and low fire hazard areas.
(2) All lines and equipment used with natural
gas must be grounded to prevent static sparks.
(3) Smoking must not be allowed. ’
(4) Non-sparking tools must be used.
11-5. Toxic materials.
Toxicity is the degree to which a substance will
affect living cells under certain conditions. It is dependent upon the dose, rate, method and site of
absorption. It is also dependent upon the health,
tolerance, diet and temperature of an individual.
Physiological effects result from inhalation, ingestion or absorption of a toxic material. To limit this
exposure, smoking and eating are not permitted in
hazardous areas, and personnel are required to
wash their hands thoroughly before eating, smoking
or using toilet facilities.
a. Mercury. Mercury metal is a distinct hazard
because of its property of vaporization at room temperature. The rate of evaporation increases with
temperature and with the surface area exposed.
This property is of great importance since mercury
can seep into human skin. Mercury or metal contaminated with mercury should never be heated
without providing exhaust ventilation or approved
air respirators.
b. Solvents. Special precautions should be taken
when working with solvents due to potential toxic
affects and flammability characteristics. Protective
measures include providing plenty of ventilation or
respirators; using rubber gloves, chemical safety
goggles, and face shields; and providing for immediate
availability of emergency eyewash facilities. Trichlorethylene and perchloroethylene are solvents suspected of being carcinogenic. The use of carbon tetrachloride as a solvent is prohibited. Acute poisoning
caused by prolonged inhalation may result in death.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
12-1. Human factor.
The protection of human life is paramount. Electrical equipment can be replaced; lost production can
be made up; but human life can never be recovered
nor human suffering ever compensated. The principal personnel dangers from electricity are that of
shock, electrocution, and/or severe burn from an
electrical arc or its effects, which may be similar to
that of an explosion. The major contributors to
work-related electrical accidents are unsafe conditions or unsafe practices. The most common unsafe
conditions are damaged, defective, burned or wet
insulation or other parts; improperly guarded or
shielded live parts; loose connections or strands
pulled loose; and equipment not grounded, or poor
or inadequate grounding connection. Unsafe practices include failing to de-energize equipment being
repaired or inspected; assuming an unsafe position
near energized equipment; using tools or equipment
too near bare energized parts; and misusing tools or
equipment. Safety manuals provided by the military services are based upon the National Electrical
Safety Code (NESC) which establishes general safe
practices for construction, maintenance, and operation of all electric utility systems. The rules contained in these manuals are considered mandatory
and must therefore be referenced at all times. Any
deviations from these procedures must be agreed
upon by the safety director. In general, to improve
safety to personnel and avoid accidents, special attention must be directed to the following:
a. Be alert. Alertness is particularly essential on
new assignments until safe habits are formed, but
should never be relaxed since conditions often
b. Be cautious. Caution should be exercised at all
c. Develop safe habits. Safe habits result from
repeated alertness and caution, and continuous adherence to the rules.
d. Know your job. Have complete and thorough
information before proceeding.
e. Observe the rules. The rules and instructions
applying to a variety of cases, both electrical and “
mechanical in nature, cover most of the common
causes of accidents.
12-2. Equipment isolation.
As a general rule, no electrical apparatus should be
worked on while it is energized. If it is not known
whether a circuit is de-energized or not, it must be
assumed that the circuit is energized and dangerous
until such time it is proven otherwise. It is also
important to regard exposed copper as energized
and treat it accordingly since copper is rarely used
except to carry current. When working near electricity, do not use metal rules or flashlights, or metallic
pencils, and do not wear watch chains, finger rings
or other objects having exposed conducting material.
a. De-energization. Personnel, who must work on
de-energized equipment, should be protected
against shock hazard and flash burns that could
occur if the circuit were inadvertently re-energized.
To provide this protection, the circuit must first be
de-energized. Check applicable up-to-date drawings, diagrams and identification tags to determine
all possible sources of supply to the specific equipment. Open the proper switches and/or circuit
breakers for each source in order to isolate the
equipment to be worked on. In cases where visible
blade disconnecting devices are used, verify that all
blades are fully open. Drawout-type circuit breakers
should be withdrawn to the fully disconnected position. Do not consider automatic switches or control
devices to be a disconnecting means for personnel
b. Tagging and lock-out. All employees should
plan for safety by following all lockout procedure
rules before beginning work on any equipment.
Four steps vital to any good lockout procedure are:
(1) Lock the equipment to prevent its use. Any
energized equipment should be shut down by turning off power or closing valves to eliminate the possibility of electrocution, the inadvertent operation of
machinery, or the release of hazardous materials.
(2) Identify the equipment to let other employees know it is not in service, when the lockout was
initiated, and the purpose of the lockout.
(3) Clear the area to assure that other employees are a safe distance from the equipment before
the lockout is tested.
(4) Test the equipment to verify that the equipment cannot be energized and that the lockout renders it inoperable. Before the test, check to be sure
that all interlocks are engaged.
(5) Once the equipment is isolated, precautions
must be taken to guard against accidental reenergization. Attach to the operating handles of the
open disconnecting devices padlocks (fig 12-1)
and/or approved red safety tags (fig 12-2). Red tags
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 12-1. Padlock and multiple lock adapter.
Figure 12-2. Typical safety tag.
are applied to devices to ensure that their positions
will not be changed by unauthorized persons as long
as equipment is blinked out and red tagged. These
tags must identify the person having the key to the
lock and the reason why the circuit is open. They
must also show the time and date of its application.
If fuses have been removed to de-energize the equipment, special precautions should be taken to prevent their unauthorized reinsertion. The following
general rules should be observed in every lockout
(a) An employee should never give a lock to
another employee.
(b) Maintenance personnel should learn
proper lockout procedures.
(c) All employees must follow correct lockout
c. Testing for voltage. After the equipment has
been de-energized, tagged and locked out, the circuit must be tested to confirm that all conductors to
the equipment are de-energized. This test is especially important on circuits which involve switches
and freed-type breakers in which the blades cannot
be visually checked. Use a volt meter or a volt-ohmmilliammeter (VOM) as described in paragraph
13-2 to test the de-energized circuit for zero volts.
Before and after testing the affected conductors,
determine that the VOM is operating satisfactorily
by testing the voltage of a source which is known to
be energized. Once these steps are completed, the
equipment is safe to work on.
d. Maintenance grounding. In spite of all precautions, de-energized circuits can be re-energized inadvertently. When this occurs, adequate maintenance
or safety grounding is the only protection for personnel. For this reason, it is especially important that
adequate grounding procedures be established and
rigidlv enforced. The tools used to apply a maintenance ground are primarily special heavy-duty
clamps which are connected to cables of adequate
capacity. These clamps and cable should not be larger
than necessary because bulkiness and weight hinder
personnel while connecting them to the conductors,
Chains, small diameter wire or battery clamps
should not be used to apply a maintenance ground
because they can easily be vaporized in the event of a
fault. Prior to application, ground cables should be
inspected for broken strands in the conductors and
loose connections to the clamp terminals, and clamp
mechanisms should be checked for defects. Defective
equipment should be replaced. Maintenance grounds
should be applied on each side of a work point, or at
each end of a de-energized circuit.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(1) Ground cables. Ground cables must be sized
for the maximum available fault current. Due to the
wide range of system voltages and fault currents, no
published standards have been developed for specific applications or locations of grounding cables. A
general survey of commercially available grounding
and related safety devices shows use of 1/0 American Wire Gauge (AWG) copper cables. This size appears to be a good compromise between a reasonable range of fault currents, the cable’s ability to
safely conduct those currents given the thermal capacity, and the ease of physically handling the particular size wire. Ground cables (fig 12-3) should be
no longer than necessary in order to keep cable
resistance as low as possible and to minimize cable
slack thereby preventing their violent movement
under fault conditions. Ground cables should be
connected first to the metal structure or switchgear
ground bus and then to a phase conductor of the
de-energized equipment. Then the ground cables
should be connected between phases and to the system neutral (when available) to minimize the voltage drop across the work area should reenergization occur. When removing maintenance
grounds, the above procedure should be reversed.
Care must be taken to remove all ground cables
before the equipment is m-energized. It is recommended that all conductors be tested with a
megohmmeter to ascertain if any are still grounded.
(2) Ground clamps. Solid metal-to-metal connections are essential between ground clamps (fig
12-4) and the de-energized equipment. Ground
clamps should have serrated jaws because it is impractical to clean conductors from paint or corrosion. The clamps should be tightened slightly in
place, given a rotation on the conductors to provide
a cleaning action by the serrated jaws, and then be
securely tightened. Ground clamps which attach to
switchgear ground bus are equipped with pointed or
cupped set screws which should be tightened to
ensure penetration through corrosion and paint, to
provide adequate connections.
12-3. Switchgear.
The following precautions should be taken when
working on switchgear.
a. Before you work on the switchgear enclosure,
remove all drawout devices, such as circuit breakers, instrument transformers, fuses and control
power transformers.
Figure 12-3. Ground cable.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 12-4. Grounding clamps.
b. Do not lay tools on the equipment while you
are working. It is too easy to forget a tool when
closing an enclosure.
c. Circuit breakers and switches are rated at
maximum capacity and must not be used beyond
this limit for fear of exploding an under-rated device.
d. If the enclosure is to be opened for any work at
all, make sure power is off the bus. The insulating
coating on the buswork is not sufficient to protect
personnel working around it.
e. Knife switches must not be used to open power
circuits, except for certain approved types of enclosed switches designed for that purpose. Before
closing a disconnecting switch, make sure that conditions are safe for such an operation. Then throw
the switch with a swift action without hesitation.
Keep the body away from the front of these enclosures when operating them. Turn your head to prevent being burned from a possible flash.
f. Maintenance closing devices for switchgear are
not suitable for closing in on an energized system.
12-4. Capacitors.
Before changing capacitor connections or doing
work of any kind on them, discharge the capacitors
with a properly insulated medium from terminal to
terminal, terminals to case, and case to ground.
Remember to keep capacitors short-circuited when
not in use.
12-5. Rotating equipment.
The safety tips below must be followed when working on rotating equipment:
a. All rotating machinery must be carefully and
thoroughly inspected for foreign objects before being
started. This inspection must cover the machine
both inside and outside. Loose articles lying on the
base, pedestals, frame or blocking may fall or be
drawn into the rotating parts; articles inside the
machine may be thrown out.
b. Do not wear neckties or any other loose clothing, or carry loose tools that may get caught in
rotating machinery.
c. At all times, the frames of all machinery, including portable hand tools, must be securely
d. While a machine is in motion or has voltage
applied, brushes shall not be shifted. Even when
inspecting brushes, the voltage should not be removed and extreme caution must be observed.
e. The commutators of DC machines must not be
cleaned while voltage is applied. If cleaning is necessary, disconnect the source of power and allow the
machine to coast while the operation is being performed.
f. Never open a field circuit unless some means
is available to limit the induced voltage. Cutting in
a discharge resistance is effective and protects an
operator from injury and the machine from damage.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
g. Rotating machinery must not be loaded or
speeded beyond their ratings.
12-6. Transformers.
Never open-circuit the secondary of a current transformer having current flowing through its primary
winding because of the resulting high induced voltages. If a current transformer has no secondary connected load, then the secondary terminals should be
shorted. The secondary windings of both current and
potential transformers must be grounded.
12-7. Wiring and testing.
Observe the safety rules below when wiring or testing:
a. Never start work or allow anyone else to start
work on any circuit until you have made certain
that the circuit has been properly de-energized,
tagged, locked-out and grounded (see para 12-2).
Inspect terminal connections and make sure that
the bolted, soldered, crimped or welded lugs are
b. Complete and inspect all wiring before making connection to the power circuit.
c. Before a plugging operation is attempted, the
apparatus and circuit must be de-energized by
opening a breaker or a switch.
d. When plugging power, first plug one end of the
cable into the “load circuit” so that no power is on
the cable. Then plug the other end firmly into an
energized receptacle. When disconnecting a plug,
reverse the sequence above.
e. When plugging to a grounded power supply
the first conductor shall be connected in the
grounded side of the circuit.
f. Whenever using a test table to operate electric
equipment on which test set controls may be “hotto-ground”, stand on an insulated floor mat.
g. At least two persons should be present in the
general area of all testing work of a hazardous nature, so that emergency assistance will be available.
h. Use only one hand whenever practical when
working on circuits or operating control devices.
i. Instruments are likely to be “hot-to-ground”,
and power shall be removed from them before any
reconnecting is attempted.
j. Carefully insulate exposed connections.
k. Under no circumstances shall cables with
damaged insulation or without terminals be used.
l. Keep wiring off an iron floor. Do not roll trucks
or other objects over any exposed cable.
m. The frames of all equipment under test or
used in test must be grounded before power is applied.
n. Whenever connection is made to power circuits,
proper protection must be afforded to both personnel
and equipment by suitable opening devices.
o. Where connection is made to a DC circuit one
side of which is grounded, one circuit breaker in the
high side is sufficient. Where neither side is
grounded, a circuit breaker must be placed on both
sides of the circuit.
p. Note identification of all circuit outlets at test
tables and switchboards, and be sure you make the
correct connection.
q. Use only portable droplights with insulated
lamp guards and handles.
r. Always test a circuit that you are to work on
for zero volts. Before and after this test, check a
circuit that is known to be energized so that the
functionability of the tester maybe verified.
s. Do not rely on the solid insulation surrounding
an energized conductor to protect personnel.
12-8. Mechanical.
Many power circuit breakers are both opened and
closed with springs. These springs may remain
charged even when a breaker has been withdrawn
from its enclosure, and are capable of operating the
breaker. If the breaker is closed, make sure the
opening spring is discharged before you approach it
with your tools or fingers. If the breaker is open,
block it and wire the trip latch. Above all, read the
manufacturer’s instructions so that you can predict
the condition of the breaker.
12-9. Danger warning and fire.
Approved danger warnings shall be used to indicate
any temporary hazard, either electrical or mechanical, and the hazard area shall be sealed off. Under
no circumstances shall this area be entered by unauthorized personnel until the warning is completely removed. Approved warning tags should be
used, and military safety standards should be referenced for marking hazardous areas. Before attempting to extinguish an electrical fire, remove the voltage. Use fire extinguisher recommended for
electrical fires but if none are available, attempt to
contain the fire with water. Do not use carbon tetrachloride in confined areas, because of the poisonous fumes that may be emitted.
12-10. Personal protective equipment
For low voltage systems, the following personal protective equipment is recommended as a minimum:
a. Hard hats—
(1) ANSI Class A—limited voltage protection.
(2) ANSI Class C-no voltage protection.
b. Safety glasses (fig 12-5).
c. Safety shoes, steel toe.
d. Rubber gloves.
e. Breathing apparatus.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 12-5. Eye and eye protection selection guide.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
13-1. Equipment maintenance.
Accurate and appropriate test equipment is critical
to the maintenance of electrical equipment. Listed
in table 13-1 are some of the tools and equipment
that each military facility electrical shop should
possess. A brief description of the equipment application is also given. To perform specialized testing,
such as infrared or insulation resistance testing,
special equipment may be rented, or purchased depending upon projected future use. This testing may
be performed by experienced military facilities personnel, or it may be contracted to an electrical testing shop. In the sections that follow three of the
more common and versatile test equipment available are described: the volt-ohm-miniammeter, the
clamp-on volt-ammeter, and the megohmmeter. As
in the use of all test equipment, these devices
should be used in strict compliance with the manufacturer’s instructions and recommendations. Failure to do so may result in injury to personnel making the tests as well as produce meaningless data.
13-2. Volt-ohm-milliammeter (VOM).
This meter incorporates the functions of the voltmeter, ohmmeter and milliammeter into one instrument. A VOM can be used to measure AC or DC
voltage, current and resistance, with several ranges
for each function. There are also solid-state VOMS
which perform the same functions. For precise operating procedures, the manufacturer’s instructions
must be referenced. A VOM which measures true
RMS should be used.
a. Safety precautions. A VOM is usually designed
to prevent accidental shock to the operator when
properly used. However, careless use of the instrument can result in a serious or fatal accident. The
VOM should only be used by personnel qualified to
recognize shock hazards and trained in the safety
precautions required to avoid possible injury. Safety
precautions are as follows:
(1) Do not work alone when making measurements of circuits where a shock hazard can exist.
Notify another person that you are, or intend to
make such measurements.
(2) Locate all voltage sources and accessible
paths prior to making measurement connections.
Check that the equipment is properly grounded and
the right rating and type of fuse(s) are installed. Set
the instrument to the proper range before power is
(3) Remember, voltages may appear unexpectedly in defective equipment. An open bleeder resistor may result in a capacitor retaining a dangerous
charge. Turn off power and discharge all capacitors
before connecting or disconnecting test leads to and
from the circuit being measured.
(4) For your own safety, inspect the test leads
for cracks, breaks or flaws in the insulation, prods
and connectors before each use. If any defects exist,
replace the test leads immediately.
(5) Do not make measurements in a circuit
where corona is present. Corona can be identified by
its sound, the odor of ozone or a pale-blue color
emanation from sharp metal points in the circuit.
(6) Hands, shoes, floor and workbench must be
dry. Avoid making measurements under humid,
damp, or other environmental conditions that could
affect the dielectric withstanding voltage of the test
leads or instrument.
(7) For maximum safety, do not touch test
leads or instrument while power is applied to the
circuit being measured.
(8) Use extreme caution when making measurements in a radio frequency (RF) circuit where a
dangerous combination of voltage could be present,
such as in a modulated RF amplifier.
(9) DO not make measurements using test
leads which differ from those originally furnished
with the instrument.
(10) Do not come into contact with any object
which could provide a current path to the common
side of the circuit under test or power line ground.
Always stand on a dry insulating surface capable of
withstanding the voltage being measured, or that
could be encountered.
(11) The range or function switch should only
be changed when the power to the circuit under
measurement is turned off. This will provide maximum safety to the user, eliminate arcing at the
switch contacts and prolong the life of the meter.
b. Operation. Before making any measurements,
the VOM pointer must be adjusted to zero. With the
VOM in operating position, check that the pointer
indicates zero at the left side of the scale when there
is no input. If pointer is off zero, adjust the screw
located in the case below center of the dial. Use a
small screwdriver to turn the screw slowly clockwise or counterclockwise until the pointer is exactly
over the zero mark at the left side of the scale. With
the indicating pointer set on the zero mark, reverse
the direction of rotation of the zero adjuster. Rotate
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 13-1. Tools and equipment for effective electrical maintenance.
TM 5-6831/NAVFAC MO-116/AFJMAN 32-1083
Table 13-1. Tools and equipment for effective electrical maintenance--continued.
the zero adjuster a sufficient amount to introduce
mechanical-freedom or “play’’ but insufficient or disturb the position of the indicating pointer. This procedure will eliminate disturbances to the zero setting from subsequent changes in temperature,
humidity, vibration and other environmental conditions. Once the VOM is zero adjusted, anyone ofa
dozen measurements canbe made. The two more
common tests are for AC voltage and resistance.
(l) AC voltage measurement. Outlined below is
the procedure for measuring voltage in a circuit. Be
careful when measuring line voltage, be sure that the
range switch is set to the proper voltage position.
(a) Set the function switch at AC (fig 13-1).
(b) Set the range switch at the desired voltage
range position. When in doubt as to the actual voltage present, always use the highes tvoltage range as
a protection to the instrument. If the voltage is
within a lower range, the switch maybe set for the
lower range to obtain a more accurate reading.
(c) Plug a test lead in the– COMMON jack
and another test lead in the + jack.
(d) Connect the test leads across the voltage
(e) Turn on power in the circuit being measured.
(f) Read the value on the scale.
(2) Resistance measurement. The procedure for
measuring resistance is outlined below.
(a) Prior to measuring a resistance, the VOM
must be adjusted to zero. Turn range switch to de-
sire ohms range (fig 13-2). Plug a test lead in the –
COMMON jack and another test lead in the + jack.
Connect ends of test leads to short the VOM resistance circuit. Rotate the ZERO OHMS control until
pointer indicates zero ohms. If pointer cannot be
adjusted to zero, one or both the VOM internal
batteries must be replaced. Before measuring resistance be sure power is off to the circuit being tested.
Disconnect the component from the circuit before
measuring its resistance.
(b) Set the range switch to one of the resistance range Positions.
(c) Set the function switch at either – DC or
+ DC. Operation is the same in either position.
Adjust ZERO OHMS control for each resistance
range as described in (a).
(d) Observe the reading on the OHMS scale
at the top of the dial. Note that the OHMS scale
reads from right to left for increasing values of resistance.
(e) To determine the actual resistance value,
multiply the reading by the factor at the switch
(f) If there is a “forward” and “backward” resistance such as in diodes, the resistance should be
relatively low in one direction (for forward polarity)
and higher in the opposite direction. Rotate the
function switch between the two DC positions to
reverse polarity. This will determine if there is a
difference between the resistance in the two directions.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 13-1. Set-up for measuring AC voltage.
13-3. Clamp-on volt-ammeter.
Most clamp-on volt-ammeters are designed to read
alternating current only, although some types are
available which will read direct current as well.
Most are provided with plug-in leads so that the
instruments can be used as voltmeters. Some models can also be used as ohmmeters. Refer to the
manufacturer’s instructions for operational procedures.
a. Application. Where a conductor is accessible at
600 volts or below, clamp-on volt-ammeters are used
simply by clamping the instrument around insulated or noninsulated conductors. Thus with no in13-4
terruption of service, the user may check motor
loads and starting current for fractional-horsepower
motors. Other applications include balancing
polyphase systems, locating overloaded feeders,
checking line voltages, trouble shooting fuse boxes
and control circuits, repairing electrical appliances,
and diagnosing miscellaneous operating problems.
Although the clamp-on volt-ammeter is easy to use,
care must be taken to obtain accurate readings. For
example, be sure that the frequency of the circuit
under test is within the range of the instrument.
Many of these instruments are calibrated at 60
Hertz. Also, take care that stray magnetic fields do
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 13-2. Set-up for measuring resistance.
not affect the current reading. When taking current
readings, try to arrange conductors so that they are
as far removed as possible from the conductor-under
test. If testing is being done in a control panel, try to
take the current readings at a location remote from
relay magnet coils which could influence the accuracy of the reading. Also, avoid taking current readings on conductors at a point close to a transformer.
Where a conductor is inaccessible at 600 volts or
below, for instance in conduit or cable troughs, current can still be measured by using a current
adapter in the fused disconnect switch. The
cartridge-fuse type has three sets of adapters for
various fuse sizes. The blade-fuse type is screwed
onto the fuse holder in the switch box. The clamp-on
ammeter function should not be used on pulsating
dc because it will give erroneous readings.
b. Accessories. A clamp-on range extender permits the measurement of high currents beyond the
range of the clamp-on volt-ammeter. The unit extends the current range ten times and allows an
actual current reading of 1000 amps AC on the
0-100A meter scale. A current multiplier permits
current measurement on low-current equipment.
The device multiplies the load current by lx, 5x or
10x. A phase sequence indicating attachment is
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
used in conjunction with the voltmeter circuit of the
clamp-on volt-ammeter. To determine phase sequence, the circuit voltage is first measured. Then
connections are made as shown in figure 13-3. If the
meter reading is higher than the original circuit
voltage, the phase sequence is black-yellow-red. If
the meter reading is below original circuit voltage
the phase sequence is red-yellow-black.
13-4. Megohmmeter.
The megohmmeter is an instrument used to measure very high resistances (fig 13-4). The megger
consists of a hand-driven direct-current generator
and a meter to indicate resistance in ohms. The
meter used is an opposed coil type, having two coils,
A and B, mounted over a gapped core (fig 13-5). The
coils are wound on a light frame, and rotate around
the core which remains stationary. The current for
the coils is supplied by the hand-driven generator.
To explain the operation of the unit, it is necessary
to examine the action of the coils with the earth and
lien terminals open; with these terminals shorted;
and with a resistance (Rx) across these terminals.
When these terminals are open, current flow is from
the generator, through B and R which are in series
with the generator. Since the terminals are open, no
current flows through coil A to oppose movement
and coil B will swing counterclockwise to a position
over the gap in the core. In this position the pointer
indicates infinity. With the terminals shorted together, a larger current flows through coil A than
through coil B and the greater force in coil A moves
the pointer clockwise to the zero position on the
scale. Resistor R’ is a current limiting resistor
which prevents damage to the meter in this situation. If a resistance is connected across the terminals, current flows through coil A, R' and the unknown resistance Rx. This current attempts to
move coil A clockwise, but the opposing force created
by current through coil B tries to move it counterclockwise. The final position of the coils is determined by the magnitude of the current through Rx’
and the coils will stop at a point where the forces
tending to move them are at a balance. The pointer
then indicates the value of the unknown resistance
on the scale. No springs are used in the movement
since the opposing forces in coils A and B balance
the pointer when a reading is being taken. Having
no springs to hinder its movement, the pointer
floats freely back and forth across the scale when
the meter is not in operation. Megohmmeters may
be obtained with different voltage ranges; the more
common being 500 and 1000 volts. The higher the
resistance range to be measured, the higher the
voltage required to actuate the movement for reading. Friction clutches are used to hold the generator
to its rated voltage output. In operation, these
clutches are designed to slip if cranked over a certain rate of speed, thus dropping the output to a
safe value.
a. Safety precautions. When operating a
megohmmeter, a very high voltage is generated at
the output terminals which could prove fatal. The
following safety precautions should be adhered to
when operating a megohmmeter.
(1) Take the equipment to be tested out of service. This involves de-energizing the equipment and
disconnecting it from other equipment and circuits.
Figure 13-3. Setup for testing phase sequence.
TM 5-683/NAVFAC MO- 116/AFJMAN 32-1083
Figure 13-5. Diagram of megohmmeter connections.
(2) If disconnecting the equipment from the circuit cannot be accomplished, then inspect the installation to determine what equipment is connected and will be included in the test. Pay
particular attention to conductors that lead away
from the installation. This is very important, because the more equipment that is included in a test,
the lower the reading will be, and the true insulation resistance of the apparatus in question maybe
masked by that of the associated equipment.
(3) Test for foreign or induced voltages with a
VOM (para 13-2). Pay particular attention once
again to conductors that lead away from the circuit
being tested and make sure they have been properly
disconnected from any source of voltage.
(4) Large electrical equipment and cables usually have sufficient capacitance to store up a dangerous amount of energy from the test current.
Therefore discharge capacitance both before and after any testing by short circuiting or grounding the
equipment under test.
(5) Apply safety grounds.
(6) Generally, there is no fire hazard in the
normal use of a megohmmeter. There is, however, a
hazard when testing equipment is located in inflammable or explosive atmospheres. Slight sparking
may be encountered when attaching test leads to
equipment in which the capacitance has not been
completely discharged or when discharging capacitance following a test. It is therefore suggested that
use of a megohmmeter in an explosive atmosphere
be avoided if at all possible. If testing must be conducted in an explosive atmosphere, then it is suggested that test leads not be disconnected for at
least 30 to 60 seconds following a test, so as to allow
time for capacitance discharge.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(7) Do not use a megohmmeter whose terminal
operating voltage exceeds that which is safe to apply to the equipment under test.
b. Operation. The following are general directions
for operating a hand-driven megohmmeter. For specific instructions, refer to the megohmmeter manufacturer’s instructions. For megohmmeter connections when testing low voltage cables or motors,
refer to paragraphs 6-3 and 4-5, respectively.
(1) Place the megohmmeter on a firm and level
base. Avoid large masses of iron and strong magnetic fields.
(2) If the megohmmeter has a selector switch,
set it to MEGOHMS + 1.
(3) Check infinity by turning the hand crank in
a clockwise direction. The pointer should move
promptly to infinity. This check is made with no
connections to the test terminals. If the reading is
not infinity, then use the INFINITY ADJUSTER to
set the pointer to infinity.
(4) Check zero by short-circuiting the testing
terminals. Turn the crank slowly. The pointer
should move promptly to zero or off the lower end of
the scale.
(5) Use well-insulated testing leads connected
to the megohmmeter terminals and with opposite
ends separated, turn the crank. If the pointer indicates less than infinity, there is a leak between the
leads which must be removed before proceeding
with tests. Touch together the test ends of the leads
while turning the crank to make certain, by a zero
reading, that the leads are not open-circuited.
(6) Apparatus to be tested must not be live. It
must be taken out of service and disconnected electrically from all other equipment (para 13-4.1).
(7) Connect leads to apparatus to be tested. For
testing to ground, connect from the LINE terminal
to a conductor of the apparatus, and from the
EARTH terminal to the frame of a machine, the
sheath of a cable or to a good ground. For testing
between two conductors, connect test leads to the
two conductors.
(8) Turn the crank in the clockwise direction
and observe the position of the pointer over the
scale. It shows the value of the insulation resistance
under test. Take the reading while operating and at
a fixed time, preferably 30 or 60 seconds.
13-5. Harmonic measurements.
The increasing use of solid-state switching devices
contributes to current wave forms which are
nonsinusoidal. This distorted current wave form results in a distorted voltage waveform. This distorted
wave form can be viewed as a fundamental 60 Hz
sine wave with odd multiples of 60 Hz harmonics
wave forms. Even harmonics are usuall y n o t
present in an AC system, except under special circumstances. The common frequency range of harmonics is O-5 kHz with O-3 Khz being most common.
If the harmonic levels are high, they may cause:
interference to control and communication lines;
heating of ac motors, transformers and conductors;
higher reactive power demand and hence poor
power factor; misoperation of sensitive electronics;
overloading of shunt capacitors and, higher power
loss. These harmonic currents will accumulate in
the neutral conductor. Therefore, it is recommended
that a double ampacity neutral conductor be used.
a. The purpose of harmonic measurements is:
(1) Monitoring existing values of harmonics
and checking against recommended or admissible
(2) Testing equipment which generates harmonics.
(3) Diagnosis and trouble-shooting situations
where the equipment performance is unacceptable
to the utility or to the user.
(4) Observations of existing background levels
and tracking the trends in time of voltage and current harmonics (daily, monthly, seasonal patterns).
b. Basic equipment used for the measurement of
nonsinusoidal voltage and currents. The techniques
used for harmonics measurements differ from ordinary power system measurement. The harmonic
measurements require more specialized instruments. Brief descriptions for three generic types of
instruments used for harmonic measurements are
included in this section.
(1) Oscilloscope. The display of the voltage
wave-form on the oscilloscope gives immediate
qualitative information on the degree and type of
distortion. Sometimes cases of resonances are
readily identifiable through the multiple peaks
present in the current wave.
(2) Spectrum analyzers. These instruments display the signal as a function of frequency. A certain
range of frequencies is scanned and all the components, harmonics and interharmonics of the analyzed signal are displayed. The display format may
be a CRT or a chart recorder. For harmonic measurements, the harmonic frequencies must be identified by reference to the fundamental frequency. A
wide range of analog and digital types of Spectrum
Analyzers are available in the market.
(3) Wave analyzers. Harmonic analyzers or
wave analyzers measure the amplitude (and also
phase angle in more complex units) of a periodic
function. These instruments provide the line spectrum of an observed signal. The cutput can be recorded or can be monitored with analogue or digital
meters. An example of these is the Dranetz 636
disturbance wave analyzer. Again instruments with
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
a wide range of capabilities are available starting
from printing results on a paper tape to automatic
storing on a personal computer. Also several different manufacturers have similar instruments.
c. The use of harmonic measurement instruments and analyses of harmonic measurement results require more sophistication. Hence, it is recommended that outside resource and manpower is
brought in for this type of work. Also if use of inhouse personnel is desired, special training of those
personnel is recommended before they are assigned
to make such measurements.
13-6. Maintenance equipment guide.
Table 13-1 recommends the tool or piece of test equipment that should be used for a particular application.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
14-1. Test evaluation.
The tests listed in this chapter are most commonly
performed to determine the condition of low voltage
equipment. If a testing program is to provide meaningful information, all tests must be conducted in a
proper manner. All conditions which would affect
the evaluation of these tests must be considered
with any pertinent factors recorded. The test operator must be thoroughly familiar with the test equip
ment used and should also be able to detect any
equipment abnormalities or questionable data during the performance of the test. To provide optimum
benefits, all testing data and maintenance actions
must be recorded. The data obtained in these tests
provide information which:
a. Determines whether any corrective maintenance or replacement is necessary or desired.
b. Ascertains the ability of the element to continue to perform its design function adequately.
c. Charts the gradual deterioration of the equipment over its service life.
14-2. Insulation testing.
Insulated electric wire is usually made of copper or
aluminum (which is known to be a good conductor of
the electric current) conductor with appropriate insulation for the rated voltage. The insulation must
be just the opposite from a conduction it should
resist current and keep the current in its path along
the conductor. The purpose of insulation around a
conductor is much like that of a pipe carrying water
(fig 14-1). Pressure on water from a pump causes
flow along the pipe. If the pipe were to “spring a
leak”, water would spout out; you would waste water and lose some water pressure. With electricity,
“voltage” is like the pump pressure causing electricity to flow along the copper wire. As in a water pipe,
there is some resistance to flow, but it is much less
along the wire than it is through the insulation.
Insulation, with a very high resistance, lets very
little current through it. As a result, the current
follows a “path of least resistance” along the conductor. The failure of an insulation system is the most
common cause of problems in electrical equipment.
Insulation is subject to many effects which can
cause it to fail; such as, mechanical damage, vibration, excessive heat, cold, dirt, oil, corrosive vapors,
moisture from processes, or just the humidity on a
muggy day. As pin holes or cracks develop, moisture
and foreign matter penetrate the surfaces of the
insulation, providing a low resistance path for leakage current. Sometimes the drop in insulation resistance is sudden, as when equipment is flooded. Usually, however, it drops gradually, giving plenty of
warning, if checked periodically. Such checks permit
planned reconditioning before service failure. If
there are no checks, a motor with poor insulation,
for example, may not only be dangerous to touch
when voltage is applied, but also be subject to bum
out. Current through and along insulation is made
up of three components (fig 14-2): capacitance
charging current; absorption current; and conduction or leakage current. The total current is the sum
of the three components and it is this current in
terms of megohms at a particular voltage that can
be measured directly by a megohmmeter. Note that
the charging current disappears relatively rapidly,
as the equipment under test becomes “charged”.
Larger units with more capacitance will take longer
to be charged. This current also is the stored energy
initially discharged after your test, by shortcircuiting and grounding the insulation. You can see
further that the absorption current decreases at a
relatively slow rate, depending upon the exact nature of the insulation. This stored energy, too, must
be released at the end of a test, and requires a
longer time than the capacitance charging
current-about four times as long as the voltage
was applied. With good insulation, the conduction
or leakage current should build up to a steady value
that is constant for the applied voltage. Any increase of leakage current with time is a warning of
trouble. With a background now of how time affects
the meaning of instrument readings, let’s consider
two common test methods: (1) short-time of spot
reading and (2) time-resistance tests.
a. Short-tin or spot-reading test. In this method,
connect the megohmmeter (para 13-4) across the
insulation to be tested and operate it for a short,
specific timed period (60 seconds usually is recommended). Commonly used DC test voltages for routine maintenance are as follows:
Equipment AC Rating
DC Test Voltage
up to 100 volts
440 to 550 volts
100 and 250 Volts
500 and 1,000 Volts
Bear in mind also that temperature and humidity,
as well as condition of your insulation affect your
reading. Your very first “spot reading” on equipment, with no prior test, can be only a rough guide
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 14-2. Curves showing components of measured current during insulation testing.
as to how “good” or “bad” is the insulation. By taking
readings periodically and recording them, you have
a better basis of judging the actual insulation condition. Any persistent downward trend is usually
fair warning of trouble ahead, even though the
readings may be higher than the suggested minimum safe values. Equally true, as long as your
periodic readings are consistent, they may be O.K.,
even though lower than the recommended minimum values. You should make these periodic tests
in the same way each time, with the same test
connections and with the same test voltage applied
for the same length of time. In table 14-1 are some
general observations about how you can interpret
periodic insulation resistance tests, and what you
should do with the result.
b. Time-resistance method. This method is fairly
independent of temperature and often can give you
conclusive information without records of past tests.
It is based on the absorption effect of good insulation compared to that of moist or contaminated insulation. You simply take successive readings at
specific times and note the differences in readings.
Tests by this method are sometimes referred to as
absorption tests (fig 14-3). Test voltages applied are
the same as those listed for the spot-reading test.
Note that good insulation shows a continual increase in resistance over a period of time. If the
insulation contains much moisture or contaminants, the absorption effect is masked by a high
leakage current which stays at a fairly constant
value-keeping the resistance reading low. The
time-resistance test is of value also because it is
independent of equipment size. The increase in resistance for clean and dry insulation occurs in the
same manner whether a motor is large or small. You
can, therefore, compare several motors and establish standards for new ones, regardless of their
horsepower ratings. The ratio of two time-resistance
readings is called a Dielectric Absorption Ratio. It is
useful in recording information about insulation. If
the ratio is a ten minute reading divided by a one
minute reading, the value is called the Polarization
Index. Table 14-2 gives values of the ratios and
corresponding relative conditions of the insulation
that they indicate.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 14-1. Interpreting insulation resistance test results.
1. Fair to high values and wellmaintained.
No cause for concern.
2. Fair to high values, but
showing a constant tendency
towards lower values.
Locate and remedy the cause and check
the downward trend
3. Low but well-maintained.
Condition is probably all right, but
cause of low values should be checked.
4. So low as to be unsafe.
Clean, dry-out, or otherwise raise the
values before placing equipment in
service (test wet equipment while
drying out).
5. Fair or high values,
previously well-maintained,
but showing sudden lowering.
Figure14-3. Typical curves showing dielectri absorption effecting
a time-resistance or double-mading test.
14-3. Protective relay testing.
Protective relays are used to detect and isolate system abnormalities with minimum disturbance to the
rest of the electrical distribution system. The more
common protective relays are the electro-mechanical
types. In them, a mechanical element, such as an
induction disk or magnetic plunger, moves in response to an abnormal change in a parameter of the
eletrical system. This movement causes a contact in
the control circuit to operate, tripping the circuit
Make tests at frequent intervals until
the cause of low values is located and
remedied; or until the values have
become steady at a lower level but safe
for operation; or until values become
so low that it is unsafe to keep the
equipment in operation.
to be applied to each particular relay, and the test
points. This data is often furnished on a timecurrent characteristic curve of a coordination study.
(4) A test instrument should be available as
recommended by the manufacturer.
(5) Most protective relays can be isolated for
testing while the electrical system is in norma operation. However, an operation of the breaker is
required to ascertain that the operation of the relay
contacts will trigger the intended reaction, such as
to trip the associated circuit breaker.
b. The tests to be performed are determined by
the relay to be tested. For electro-mechanical relays, inspection, testing and adjustment are recommended.
(1) Inspection. Each relay should be removed
from its case for a thorough inspection and cleaning.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Table 14-2. Condition of insulation indicated by dielectric absorption ratios.
Less than 1
1.0 to
1.0 to 2
1.4 to 1.6
2 to 4
Above 1.6 **
Above 4 **
*These values must be considered tentative and relative
with the time-resistance method over a period of time.
- subject
**In some cases, with motors, values approximately 20% higher than shown here
indicate a dry brittle winding which will fail under shock conditions or during
maintenance, the motor winding should be cleaned,
treated, and dried to restore winding flexibility.
If the circuit is in service, remove one relay at a
time so as no to totally disable the protection. Before the relay cover is removed, excessive dirt, dust
and metallic material deposited on the cover should
be noted and removed.Removing such material will
prevent it from entering the relay when the cover is
taken off. The presence of such deposits may indicate the need for some form of air filtering at the
station. "Fogging’’ of the cover glass should be noted
and cleared. Such fogging is, in some cases, a normal condition due to volatile materials being driven
out of coils and insulation. However, if the fogging
appears excessive, further investigation is necessary. A check of the ambient temperature and the
supplied voltage and current must be compared to
the nameplate or manufactured instruction book
(2) Electrical tests. Manually close (or open) the
relay contacts and observe that they perform their
required function; i.e., trip a breaker, reclose a
breaker, etc. Apply prescribed settings or ascertain
that they have been applied to the relay. Gradually
apply current or voltage equal to the tap setting to
the relay to verify that the pickup is within specified limits. If miscalibrated, the restraining spiral
spring can be adjusted. The data that this test
yields should be compared to previous data. Reduce
the current or voltage until the relay drops out or
resets fully. This test will indicate excess friction.
Should the relay be sluggish in resetting or fail to
reset completely, then the jewel bearing and pivot
should be examined. A magnifying glass is adequate
for examining the pivot, and the jewel bearing can
be examined with the aid of a needle which will
reveal any cracks in the jewel. Should dirt be the
problem, the jewel can be cleaned with an orange
stick while the pivot can be wiped clean with a soft,
lint-free cloth. No lubricant should be used on either
the jewel or pivot. Should evidence of overheating
be found, the insulation should be checked and if
brittle replaced. Withdrawal of the connection plug
in drawout relays may reveal evidence of severe
fault currents or contaminated atmospheres, either
of which may indicate that a change in the maintenance schedule is necessary.
(3) Mechanical adjustments. All connections
should be tight. If several connections are loose,
excessive vibration may be indicated, and should be
corrected. All gaps should be free of foreign materials, if not, inspection of the gasket is necessary.
Contact gaps should be measured and the values
compared with pervious measurements. Should
there be a large variation in these measurements,
excessive wear may be indicated, in which case the
worn parts should be replaced. It may also be found
that an adjusting screw has worked loose and must
be retightened. This information should be noted on
the test record. All contacts, except those not recommended for maintenance, should be burnished and
measured for alignment and wipe. Relays that operate after a time delay when subjected to an overcurrent condition should have an operating time test
performed. This test is made anywhere from two to
ten times tap setting. The time it takes the relay to
trip must coincide with the manufacturer's recommended operating times. If not, then relay adjustments should be made, if possible and the relay
retested. Readjustments may be necessary until the
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
relay operates within acceptable limits. Tests
should be made with the relay in its panel and case,
and the time tests run at the calibrated setting. For
precise testing procedures, manufacturer’s instructions should be consulted. Some protective relays
operate instantaneously; that is, with no intentional
time delay. They should be set by test. Most types of
protective relays have a combination target and
seal-in unit. The target indicates that the relay has
operated; the seal-in holds the relay contacts closed.
It should be verified that the target is functional
and that the relay will seal-in with the minimum
specified DC current applied to the seal-in unit.
14-4. Equipment ground resistance testing.
An equipment ground is a connection to ground
from one or more noncurrent-carrying m e t a l p a r t s
of the equipment (para 8-2b). Instrument are available to determine if the grounding path is continuous and has sufficiently low resistance. When using
these instruments, one should remember that although a high resistance value is an indication of a
problem, for example a loose connection or excessive
conductor length, a low resistance reading does not
necessarily indicate the adequacy of the grounding
path. A grounding path that is found to have a low
resistance may not have sufficient capacity to
handle large ground faults. Visual examinations
and torquing connections are still needed to determine that adequacy of the grounding path.
with the seasons, and one earth resistance reading
alone with not guarantee a safe earth ground.
c. Grounding system. As the grounding electrode
is placed further into the earth the ground resistance decreases (fig 14-7), and there is less resistance change due to temperature and moisture
variations. Changing the diameter of the electrode
has little effect on ground resistance. An electrode
(fig 148) is pictured surrounded by hemispheres of
equal thickness and composed of the same type of
soil. Each additional hemisphere away from the
electrode increases in area. As the hemisphere’s
area increases, the resistance decreases- In effect,
the earth resistance is the sum of all the hemisphere resistances. A point will be reached where
the addition of new hemispheres will not effectively
change the total resistance. This will be the value of
the earth resistance.
(1) Precautions. All earth resistance testing
methods can involve hazards to the operator. Precautions should be taken as follows:
Electrode to earth
14-5. System ground resistance testing.
A system ground is a connection to ground from one
of the current- carrying conductors (para 8-2c). An
adequately grounded system is necessary to provide
for ground fault protections and to reduce the hazards of fire and shock to personnel. A system ground
or earth resistance test has been developed to determine the effectiveness and integrity of the grounded
system. Periodic testing is recommended based
upon the importance of the ground system. The
current flowing through an earth electrode encounters three basic resistive components: electrode;
electrode-to-earth; and earth (fig 144). The earth
resistance is the largest of the three resistance components. The earth resistance depends on the following:
a. Type of soil. As the soils composition varies so
does the corresponding resistance values. Also as
the soil becomes more closely packed, the resistance
becomes less.
b. Moisture and temperature of soil. When a soil
dries out, or its temperature is lowered, the soils
resistance value increases (figs 14-5 and 14-6).
Therefore, resistance values measured will vary
Figure 14-4. Resistive components of a made electrode.
Percent moisture in soil
Figure 14-5. Soil resistivity vs. moisture content of red clay soil.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Earth surface
E l e c t r o d e
Figure 14-8. Earth electrode with hemispheres.
Figure 14-6. Soil resistance vs. temperature of clay soil.
Depth of electrode in feet
Figure 14-7. Soil resistance vs. depth of electrode.
(a) When testing earth resistance, remember
that during fault conditions, dangerous voltages
may exist between a system ground and a remote
point being tested. Care should be taken when connecting leads and test equipment, Avoid as much
contact with the leads and probes as possible.
(b) Most of the earth resistance is located
close to the grounding system due to the “hemisphere effect”. When a ground fault occurs, the majority of the voltage drop is close to the system.
Caution should be used when approaching a live
(c) At stations where the fence is not connected to the station ground, a dangerous voltage
can develop under fault conditions between the
fence and station ground. Do not touch both at the
same time.
(d) Surge and switching effects in transmission lines may induce dangerous spikes in the test
leads strung under the line. Care should be exercised in handling these test leads.
(e) Tests should not be performed during a
(2) Protection. Rubber gloves, boats, an insulated platform, etc., capable of protecting the operator against full-line voltage, are recommended for
(3) Fall-of-potential method. The fall-ofpotentiaI method is probably the most widely used
and accepted of all methods available. It can be
used most practically on small and medium sized
systems. A ground resistance test set is used. Measure the earth resistance of the earth system (E) (fig
14-9). In this method, greater pin spacing is required for testing ground grids and multiple rod
installations than for single rod testing. To accomplish this, current is supplied between the current
electrode (CE) and the system E under test. A voltmeter measures the voltage drop between the potential electrode (PE) and the system. By moving
the potential electrode between E and CE, various
voltages will be recorded and corresponding resistance values found. When the resistance values are
plotted versus distance, the earth resistance can be
seen to increase as the potential electrode moves
away from the system ground, but at a decreasing
rate of change. This results because each new outer
hemisphere of earth around the system E adds a
smaller amount of resistance to the total earth resistance as previously discussed. At a point, usually
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
d. The hydrometer must be held vertical such
that the float is free and not in contact with the
sides of the hydrometer barrel.
e. With hydrometer floating freely, read and
record the float scale point at the true liquid level
(fig 14-11). The level at point A is 1.210; at point B,
where the float is lower in the liquid, the reading is
14-7. Infrared inspection.
Figure 14-9. Fall-of-potential method graph.
about 62 percent
of the total distance between the
current probe and the system, the earth resistance
should become almost constant. This is the point
where the earth resistance of the system is most
14-6. Battery specific gravity test.
Great care should be exercised when sampling and
handling battery electrolyte. Since it may contain
acid it can cause irritation if it comes in contact
with the skin, and could cause blindness if it were
splashed in the eye. Electrolyte is also a conductor
and can cause short circuits if splashed over the cell
terminals. When specific gravity of a battery is being measured, wear acid resistant eye protection,
gloves and apron. It is also available to wear rubber
slippers or boots when working with batteries.
When sampling the cells’ electrolyte:
a. Place a hydrometer tube (or hose) firmly into
the mouth of the cell electrolyte withdrawal tube
(fig 14-10).
b. Slowly squeeze the hydrometer bulb so as to
force air into the withdrawal tube, clearing it of
c. Release hand pressure on the hydrometer bulb
allowing electrolyte to draw up into the glass barrel of
the hydrometer. Sufficient electrolyte must be withdrawn to allow the hydrometer float to float freely.
Infrared thermography is the process of making inframed radiation visible and measurable. This radiation is emitted by all objects as heat, which is constantly being absorbed and re-emitted by
everything including ourselves. When an electrical
connection is loose or corroded, it is said that the
conductor has developed a high resistance connection. A high resistance connection produces heat
which can be detected through infrared thermography. Loose connections should be tightened
and corroded connections cleaned. Cables with poor
insulation should be repaired or replaced. Infrared
inspections of electrical equipment help to reduce
the number of costly and catastrophic failures and
unscheduled shutdowns. Such inspections performed by qualified and trained personnel on energized equipment may uncover potentially dangerous situations. Proper diagnosis and remedial
action have also helped to prevent major losses. The
instruments most suitable for infrared inspections
are of the type that use a scanning technique to
produce an image of the equipment being inspected.
These devices display a picture, where the “hot
spots” appear as bright spots. Infrared surveys may
be performed by military facilities personnel if they
own infrared imaging instruments and adhere to
the manufacturer’s instructions. Routine infrared
surveys should be performed at the very least every
year during periods of maximum possible loading.
These surveys should be well documented and if
critical, impending faults exist, the electrical supervisor should be notified and corrective actions
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 14-10. Sampling the cell electrolyte.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 14-11. Reading the hydrometer flint.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083/
15-1. Personnel.
This chapter sets up timetables for maintenance
actions. Whenever the electrical shop/electrician or
the electrical supervisor is mentioned, it refers to
the appropriate shop or individual responsible to
the facilities engineer, the public works officer, the
base civil engineer or to the appropriate individual
having responsibility for the maintenance of real
property facilities. The user or using service is the
occupant actually benefiting from the service. The
maintenance group consists of personnel who are
responsible for the routine scheduled maintenance
of real property facilities. This group may or may
not have affiliated electrical personnel. The operator has the responsibility for starting, operating and
securing the equipment when not in use.
15-2. Responsibilities.
The responsibility for maintenance of all real property electrical items will be assigned to the electrical shop/electrician. For example, the electrical
shop/electrician is responsible for electric motors
and pertinent controls that power such equipment
as air conditioners, boilers and water pipes, even
though the overall responsibility for the powered
equipment is assigned to other shops. While most of
the electrical maintenance will be accomplished by
personnel in the electrical shop/electrician, it is often more logical and economical to have certain
tasks, particularly preventive maintenance, accomplished by other personnel. Such tasks will be determined by the electrical supervisor who, through coordination and inspection, assures adequacy of the
work performed. Often the user or other shops have
the capability to perform periodic electrical maintenance. For example, air conditioning mechanics
generally have the capability to service motors and
controls associated with their responsibilities. In
designating tasks for others, the electrical supervisor will be guided by their capabilities. In tables
15-3 and 15-4 entries in the column headed "responsibility” indicate the suggested groups that might be
expected to perform the listed maintenance work at
typical military installations. These suggested assignments may be changed to suit local conditions
and capabilities.
15-3. Frequencies and procedures.
Of many factors involved in reliability of equipment, timely and high quality preventive mainte-
nance are very important. A properly developed and
implemented electrical preventive maintenance
program minimizes equipment failure. However,
performing maintenance at too frequent intervals is
expensive, both in labor and material costs, but
sometimes this can also cause failure. Thus there is
a general optimum interval between scheduled preventive maintenance instances. Table 15-1 lists the
data regarding percentage of failures since last
maintenance. From this table, the following conclusions regarding maintenance frequency can be
a. One year or less interval for scheduled maintenance of all electrical equipment combined as a
general rule is desirable.
b. One year interval for circuit breaker is appropriate.
c. Two year interval for motors (DC motors may
need more frequent maintenance compared to AC
motors) should be sufficient (bearings may need
more attention).
d. Two year interval for transformers.
e. This interval needs to be adjusted for specific
equipment, type of duty, operating environment and
quality of maintenance. Quality of maintenance can
be factored into the failure rate by using multipliers
shown in table 15-2. For example, poor quality of
motor maintenance will double (1.97 in table 15-2)
its failure rate for the same maintenance interval,
whereas perfect maintenance reduces the failure
rate (given in table 15-4) by 16 percent. The preventive maintenance inspection and service frequencies
that follow (tables 15-3 and 15-4) are guides which
may be modified to meet local requirements. Whenever manpower constraints prevent the facilities
manager in following the suggested maintenance
frequency, procuring outside contractors is an option. However, if budgetary constraints make this
an impossible task, then maintenance should be
scheduled as close to the suggested interval as possible. Exceptions should not be made for maintaining equipment and facilities which serve critical
loads and functions. The maintenance group or user
should immediately report any defects beyond their
repair capability to the electrical shop/electrician.
They should keep records of all defects in the system and corrective actions taken to repair these
defects. The table inputs are self-explanatory. The
references are to sections in this manual covering
procedures of inspections and maintenance.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083/
Table 15-1. Percentage of failure caused since maintained.
*small sample size; less than 7 failures caused by inadequate maintenance.
Table 15-2. Equipment failure rate multipliers versus maintenance quality.
Tables 15-1 and 15-2 reproduced here from ANSI/IEEE Std 493-1980, IEEE
Recommended Practice for Design of Reliable Industrial and Commercial Power
Systems, copyright C 1985 by The Institute of Electrical and Electronics
Engineers, Inc., with permission of the IEEE Standards Department.
Note: The Navy will follow inspection and service
frequencies as established in this section. Modifications will be made as required by NAVFAC MO-322,
Inspection for Maintenance Public Works and Public Utilities, and Volume 2, Inspection GuidesElectrical.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083/
Table 15-3. Interior wiring and lighting system.
Maintenance Group
Each scheduled
building visit
Unauthorized or nonstandard attachments
Defective convenience outlets and switches.
Improper cords.
Proper fuse sizes in panels.
Overheating of panels.
Any condition likely to cause fire. Check batterytype emergency lights and replacement lamps.
Check for Iamps larger than standard prescribed
for outlet.
A S Required
Replace burnt out lamps in hard-to-reach places.
(To be accomplished by electrical shop if special
equipment such as ladder trucks are needed).
Panels for circuit idenificaton and accessibility.
Replace blown fuses.
Replace burnt out or defective incandescent lamps.
Replace burnt out fluorescent lamps if personnel
have been instructed in this function and if assigned
to user. Promptly replace or report defective
lamps since a lamp approaching bum out flashes on
and off, causing overduty on auxiliary equipment.
As required.
Make repairs and adjustments to systems when
malfunctions are reported. Ensure that all work
complies with the NEC
As required.
Check ground resistance for special weapons
facilities at request of user.
Check for low voltages and/or low power factor.
Monthly or
Inspect station (substation switchgear or UPS) as
(1) Check electrolyte level and add distilled water if
(2) Check charging rate. Adjust charging rate as
necessary to maintain proper specific gravity.
(3) Test for proper operation under simulated
power interruption. Check maintenance free
batteries. Check voltage, check and clean
Table 15-3. Interior wiring and lighting system-continued.
As required
Infrared scan, if available, and inspect
buildings for defective wiring and loose
connections. Tighten or replace, as
necessary. Check grounds for continuity.
Check all systems for abnormal conditions.
Correct discrepancies.
Inspect disconnects, cabinets, panels and load
centers. Tighten connectionss. Clean panels.
Check fuse sizes. Manually operate switches
and breakers.
Use ohmmeter to detect grounds. Eliminate
Check and correct unbalance of loads
Clean transformers, ducts and capacitors.
As required
3, 24,
Clean lighting fixtures whenever foot-candle
readings drop 20 to 25%. This will beat
approximate ly annual intervals in ordinary
offices, longer in clean rooms, and at lesser
intervals for dirty areas. Work should be
accomplished by custodial or by user if
within capabilities.
Electrical Shop
Every Year
Every 5 years
Test power circuit breakers and protective
Test metering and indicating instruments
2-8-4, 28-5, 2-87
Test molded case feeder and main circuit
breakers in main panelboards.
Test single phase watt hour meters.
Table 15-4. Electric motors and controls.
As Required
Report any unusual conditions. Clean and lubricate those
motors assigned to the team for this purpose
As Required
Kcep area around motors free from obstructions.
Report any:
(1) Unusual noises
(2) Overheating
(3) Accumulation of dust and moisture
(4) Sparking
(5) Difficulty in coming up to speed
Check oil level on sleeve bearing motors with oil gages.
Fill, if necessary. Add oil and check only when motor is
Check belts for suitable slack.. Adjust as necessary.
Aa required
Check brushes in holders for fit and free play. Tighten
brush studs. Replace brushes if necessary.
Inspect commutator for high mica. glaze, roughness or
Check for vibration.
Check shunt, series, and commutating fields or tightness.
Check cable connections.
Check for bearing wear. Lubricate ball bearings.
Measure insulation resistanc e on motars over 10 hp.
Check winding insulation for cracks or other defects.
Make sure windings are dry.
Check air gap between rotor and stator on motors over 1
horsepower. Use long feeler gages for this purpose. A
record of yearly checks will give a picture of bearing wear.
A variation of 10 percent from one year to the next is
Cheek belts to insure that they are no tighter than necessary
to insure against slipping. Check chains for evidence of
Maintain proper alignment between motor and machine that
it drives.
Check motor to see that end thrust is not excessive and
shaft has a reasonable axial float.
Lubricate motors. Flush and refill oil reservoirs. USe
lubricants recommended by equipment manufacture.
Frequency of lubrication depends on usage of motors.
Grease lubricated ball or roller bearing motors may require
lubrication only once a year if motor is operated lightly,
but as often as every 2 months if hard driven. Do not mix
greases of different type or specifications.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083/
Table 15-4. Electric motors and controls-continued.
TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
A-1. Government Publications
Department of the Army
Facilities Engineering; Reports
AR 420-16
Electrical Services
AR 420-43
Fire Protection
AR 420-90
Military Custodial Services Manual
TM 5-609
Facilities Engineering; Electrical Facilities Safety
TM 5-682
Facilities Engineering Electrical Exterior Facilities
TM 5-684
Maintenance of Fire Protection Systems
TM 5-695
Interior Wiring
TM 5-760
Electric Power Supply and Distribution
TM 5-811-1
Electrical Design; Interior Electrical System
TM 5-811-2
Electrical Design; Lightning and Static Electricity Protection
TM 5-811-3
Department of the Navy
Technical Coordination and Support of the Maintenance of Public Works and Public
Public Works Types Maintenance Problems Arising from Field Operation Experience
Fire Alarm and Sprinkler Maintenance
Electrical Exterior Facilities
Operation of Electric Power Distribution System
Control of Electromagnetic Interference on Overhead Power Lines
Wire Communication and Signal System Maintenance
Electrical Power System Analysis
Central Heating and Steam-Electric Generating Plants
Operation and Maintenance of Internal Combustion Engines
Department of the Air Force
Air Force Occupational Safety and Health (AFOSH) Standards, Department of
Labor Occupational Safety and Health (OSHA) Standards, and National Institute for Occupational Safety and Health (NIOSH) Publication
of Electric Power Plants and Generators
API 32-1062
Supply and Distribution
AFJMAN 32-1080
Interior Electrical Systems
AFJMAN 32-1081
Design, Lightning and Static Electricity Protection
A.FM 88-9
Facilities Engineering, Electrical Exterior Facilities
AFJ MAN 32-1082
Electric Power Systems
AFI 32-1063
Grounding Systems
AFI 32-1065
Electrical Safety in Medical Facilities
AFI 41-203
Visual Air Navigation Systems
AFI 32-1044
A-2. Nongovenment Publications
American National Standards Institute (ANSI), National Electric Safety Code, Standard C2, 1993, 1430
Broadway, New York, NY 19918
Illuminating Engineer Society (IES), IES Handbook, 1987, 345 East 47th Street, New York, NY 10017
Institute of Electrical and Electronics Engineers (IEEE), Guide for Field Testing of Relaying Current
Transformers IEEE Standard C57.13-1-1981, 345 East 47th Street, New York, NY 10017
Institute of Electrical and Electronics Engineers (IEE), IEEE Recommended Practice for Grounding of
Industrial and Commercial Power Systems, IEEE Standard 142-1982, 345 East 47th Street, New York, NY
Institute of Electrical and Electronics Engineers (IEEE), ZEEE Recommended Practice for Power Systems
Analysis, IEEE Standard 399-1980, 345 East 47th Street, New York, NY 10017
Institute of Electrical and Electronics Engineers (IEEE), IEEE Recommended Practice for Protection and
Coordination of Industrial and Commercial Power Systems, IEEE Standard 242-1986,345 East 47th Street,
New York, NY 10017
Institute of Electrical and Electronics Engineers (IEEE), IEEE Recommended Practice on Surge Voltages
in Low Voltage AC Power Circuits, IEEE Standard C62.41-1991, 345 East 47th Street, New York, NY 10017
National Electrical Manufacturers Association (NEMA), Enclosures for Electrical Equipment, NEMA
Standard 250-1991, 2101 L Street, NW, Washington, DC 20037
National Electrical Manufacturers Association (NEMA), Guidelines for Inspectionn and Preventative
Maintenance of Molded Case Circuit Breakers Used in Commercial and Industrial Applications, NEMA
Standard AB 4-1991, 2101 L Street, NW, Washington, DC 20037
National Fire Protection Association (NFPA), National Electrical Code, NFPA publication #70, 1990, 1
Batterymarch Park, Quincy, MA 02269
National Fire Protection Association (NFPA), Recommended Practice for Electrical Equipment
Mainte- nance, NFPA publication #70B, 1990, 1 Batterymarch Park, Quincy, MA 02269
National Fire Protection Association (NFPA), Installation, Maintenance, and Use of Protective Signaling
Systems, NFPA publication #72, 1990, 1 Batteryrmarch Park, Quincy, MA 02269
National Fire Protection Association (NFPA), Fire Tests of Building Construction and Materials, NFPA
publication #251, 1990, 1 Batterymarch Park Quincy, MA 02269
Underwriters Laboratories (UL), UL Standard for Safety: Molded Case Circuit Breakers and Circuit
Breaker Enclosures, UL #489-1991, 207 East Ohio Street, Chicago, IL 60611
TM 5-83/NAVFAC M-116/AFJMAN 32-1083
The proponent agency of this publication is the United States
Army Center for Public Works. Users are invited to send comments and suggested improvements on DA Form 2028 (Recommended Changes to Publications and Blank Forms) directly to
Director, U.S. Army Center for Public Works, Attn: CECPW-EE,
7701 Telegraph Rd., Alexandria, VA 22315-3862.
By Order of the Secretaries of the Army, the Navy, and the Air Force:
General, United States Army
Chief of Staff
Rear Admiral CEC, USN Commander,
Naval Facilities Engineering Command
The Civil Engineer
Army: To be distributed in accordance with DA Form 12-34-E, block
0695 requirements for TM 5-683.
Air Force: F
*U.S. G. P.O. : 1996-404-611 :20046
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