SB800 - Marathon Motors Basic Training Manual

SB800 - Marathon Motors Basic Training Manual
Electric Motors
Gear Reducers
Gear Motors
Variable Speed Drives
A Regal Brand
Basic training for
industrial-duty and
commercial-duty products.
Basic Training
Industrial-Duty & Commercial-Duty
Electric Motors
Gear Reducers
AC & DC Drives
A Publication Of
Copyright ©2013
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Electric Motor History and Principles
II. General Motor Replacement Guidelines . . . . . . . . . . . 8
III. Major Motor Types . . . . . . . . . . . . . . . . . . . . . . . . . . 15
AC Single Phase
AC Polyphase
Direct Current (DC)
Motors For Precise Motor Control
Permanent Magnet (PMAC) Motors
Benefits of PMAC Motor
IV. Mechanical Considerations . . . . . . . . . . . . . . . . . . . . . 22
Enclosures and Environment
NEMA Frame/Shaft Sizes
NEMA Frame Suffixes
Frame Prefixes
Types of Mounts
Application Mounting
Motor Guidelines for Belted Applications
V. Electrical Characteristics
and Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Current (Amps)
Insulation Class
Service Factor
Thermal Protection (Overload)
Shaft Grounding Devices
Faraday Shield
Grounding Brush
Shaft Grounding Ring
Insulated Bearings
Torque Speed Characteristics
Individual Branch Circuit Wiring
Motor Starters
Across the Line Starting of Induction Motors
Magnetic Starters
Reduced Voltage Starters
Primary Resistance Starters
Autotransformer Starters
Wye-Delta Starting
Part Winding Starters
Reading a Model Number
Major Motor Components
VI. Metric (IEC) Designations . . . . . . . . . . . . . . . . . . . . . . 56
IEC / NEMA Dimensional Comparison
IEC Enclosure Protection Indexes
IEC Cooling, Insulation and Duty Cycle Indexes
IEC Design Types
IEC Mounting Designations
VII. Motor Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Lubrication Procedure
DC Motor Trouble-Shooting
AC Motor Trouble-Shooting
Relubrication Interval Chart
VIII. Common Motor Types and
Typical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Alternating Current Designs
Elevator Motors
Direct Current Designs
IX. Gear Reducers and Gearmotors . . . . . . . . . . . . . . . . . 75
Right-Angle Worm Gear Reducers
Parallel-Shaft Gear Reducers
Installation and Application Considerations
Special Environmental Considerations
Gear Reducer Maintenance
X. Adjustable Speed Drives . . . . . . . . . . . . . . . . . . . . . . 84
DC Drives
AC Drives
“One Piece” Motor/Drive Combinations
AC Drive Application Factors
Motor Considerations With AC Drives
Routine Maintenance of Electrical Drives
XI. XII. Engineering Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Temperature Conversion Table
Mechanical Characteristics Table
Electrical Characteristics Table
Fractional/Decimal/Millimeter Conversion
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Electric Motor History and Principles
The electric motor in its simplest terms is a converter of electrical
energy to useful mechanical energy. The electric motor has played a
leading role in the high productivity of modern industry, and it is therefore directly responsible for the high standard of living being enjoyed
throughout the industrialized world.
The beginnings of the electric motor are shrouded in mystery, but this
much seems clear: The basic principles of electromagnetic induction
were discovered in the early 1800’s by Oersted, Gauss and Faraday, and
this combination of Scandinavian, German and English thought gave us
the fundamentals for the electric motor. In the late 1800’s the actual
invention of the alternating current motor was made by Nikola Tesla, a
Serb who had migrated to the United States. One measure of Tesla’s
genius is that he was granted more than 900 patents in the electrical
field. Before Tesla’s time, direct current motors had been produced in
small quantities, but it was his development of the versatile and rugged
alternating current motor that opened a new age of automation and
industrial productivity.
An electric motor’s principle of operation is based on the fact that a current-carrying conductor, when placed in a magnetic field, will have a force
exerted on the conductor proportional to the current flowing in the conductor and to the strength of the magnetic field. In alternating current
motors, the windings placed in the laminated stator core produce the
magnetic field. The aluminum bars in the laminated rotor core are the
current-carrying conductors upon which the force acts. The resultant
action is the rotary motion of the rotor and shaft, which can then be
coupled to various devices to be driven and produce the output.
Many types of motors are produced today. Undoubtedly, the most
common are alternating current induction motors. The term “induction” derives from the transference of power from the stator to the
rotor through electromagnetic induction. No slip rings or brushes are
required since the load currents in the rotor conductors are induced by
transformer action. The induction motor is, in effect, a transformer - with
the stator winding being the primary winding and the rotor bars and end
rings being the movable secondary members.
Both single-phase and polyphase (three-phase) AC motors are
produced by Marathon Motors and many other manufacturers. In
polyphase motors, the placement of the phase winding groups
in conjunction with the phase sequence of the power supply line produces a rotating field around the rotor surface. The
rotor tends to follow this rotating field with a rotational speed that
varies inversely with the number of poles wound into the stator. Singlephase motors do not produce a rotating field at a standstill, so a starter
winding is added to give the effect of a polyphase rotating field. Once
the motor is running, the start winding can be cut out of the circuit,
and the motor will continue to run on a rotating field that now exists
due to the motion of the rotor interacting with the single-phase stator
magnetic field.
The development of power semiconductors and microprocessors has
brought efficient adjustable speed control to AC motors through the use
of inverter drives. Through this technology, the most recent designs of
so-called pulse width modulated AC drives are capable of speed and
torque regulation that equals or closely approximates direct current
Marathon Motors also produces permanent-magnet direct current
motors. The DC motor is the oldest member of the electric motor family. Technological breakthroughs in magnetic materials, as well as solid
state electronic controls and high-power-density rechargeable batteries,
have all revitalized the versatile DC motor.
DC motors have extremely high torque capabilities and can be used
in conjunction with relatively simple solid state control devices to give
programmed acceleration and deceleration over a wide range of
selected speeds. Because the speed of a DC motor is not dependent
on the number of poles, there is great versatility for any constant or variable speed requirement.
In most common DC motors, the magnetic field is produced by highstrength permanent magnets, which have replaced traditional field coil
windings. The magnets require no current from the power supply. This
improves motor efficiency and reduces internal heating. In addition, the
reduced current draw enhances the life of batteries used as power supplies in mobile or remote applications.
Both AC and DC motors must be manufactured with a great deal of
precision in order to operate properly. Marathon Motors and other major
manufacturers use laminated stator, rotor and armature cores to reduce
energy losses and heat in the motor. Rotors for AC motors are heat
treated to separate the aluminum bars from the rotor’s magnetic
laminations. Shaft and bearing tolerances must be held to ten
thousandths of an inch. The whole structure of the motor must be
rigid to reduce vibration and noise. The stator insulation and coil
winding must be done in a precise manner to avoid damaging the wire
insulation or ground insulation. And mountings musts meet exacting
dimensions. This is especially true for motors with NEMA C face
mountings, which are used for direct coupling to speed reducers,
pumps and other devices.
The electric motor is, of course, the very heart of any machine it drives.
If the motor does not run, the machine or device will not function. The
importance and scope of the electric motor in modern life is attested to
by the fact that electric motors, numbering countless millions in total,
convert more energy than do all our passenger automobiles. Electric motors
are much more efficient in energy conversion than automobiles, but they
are such a large factor in the total energy picture that renewed interest is
being shown in motor performance. Today’s industrial motors have energy
conversion efficiency exceeding 96% in larger horsepowers.
This efficiency, combined with unsurpassed durability and reliability,
will continue to make electric motors the “prime movers” of choice for
decades to come.
General Motor Replacement Guidelines
Electric motors are the versatile workhorses of industry. In many applications, motors from a number of manufacturers can be used.
Major motor manufacturers today make every effort to maximize
interchangeability, mechanically and electrically, so that compromise
does not interfere with reliability and safety standards. However, no
manufacturer can be responsible for misapplication. If you are not
certain of a replacement condition, contact a qualified motor distributor,
sales office or service center.
Safety Precautions
Use safe practices when handling, lifting, installing, operating, and
maintaining motors and related equipment.
Install motors and related equipment in accordance with the
National Electrical Code (NEC) local electrical safety codes and
practices and, when applicable, the Occupational Safety and Health
Act (OSHA).
Ground motors securely. Make sure that grounding wires and
devices are, in fact, properly grounded.
Failure to ground a motor properly
may cause serious injury.
Before servicing or working near motor-driven equipment, disconnect
the power source from the motor and accessories.
Identifying a motor for replacement purposes or specifying a motor for
new applications can be done easily if the correct information is known.
This includes:
Mechanical requirements of the driven load
Physical and environmental considerations -8-
Efficiency and economic considerations
Electrical Characteristics and Connections
Much of this information consists of standards defined by the National
Electrical Manufacturers Association (NEMA). These standards are
widely used throughout North America. In other parts of the world,
the standards of the International Electrotechnical Commission (IEC) are
most often used.
Driven Load - Mechanical requirements
For a motor to drive a load properly, It must produce enough
torque to accelerate from standstill to operating speed, and to
supply enough power for all possible demands without exceeding
its design limits.
To specify the motor properly, the following characteristics of the
load should be considered:
1) Running characteristics:
• Continuous running, constant load.
- horsepower requirement
• Continuous running, varying load
- peak horsepower requirement
• Cyclical load
- peak torque and horsepower requirements
2) Speed
• Constant speed
• Multi-speed
- what speeds required?
• Adjustable speed
- determine needed speed range
3) Starting and Stopping
• Frequency of starting and stopping
• Starting torque requirement
• Acceleration restrictions
• Requirements for braking
- mechanical
- plugging
From this information the size and design characteristics of the motor, as
well as control and braking requirements can be determined.
Physical and Environmental Consideration
Usual Service Conditions
Motor ratings apply to motors operating under usual service conditions.
NEMA and EEMAC (Electrical Equipment Manufacturers Association of
Canada) standards specify usual environmental conditions as:
1. Exposure to an ambient temperature in the range of 0º to 40ºC or
when water cooling is used, in the range of 10º to 40ºC.
2. Exposure to an altitude which does not exceed 3300 feet (1000
meters) (see MG1-14.04)
3. Installation on a rigid mounting surface
4. Installation in areas or supplementary enclosures which do not
seriously interfere with the ventilation of the machine
Unusual Service Conditions
The manufacturer should be consulted if the motor is to be operated in
unusual service conditions.
NEMA and EEMAC standards also specify typical unusual service
1) Exposure to:
• Combustible, explosive, abrasive or conducting dusts
• Lint or very dirty operating conditions where the accumulation of
dirt may interfere with normal ventilation
• Chemical fumes, flammable or explosive gases
• Nuclear radiation
• Steam, salt-laden air, or oil vapor
• Damp or very dry locations, radiant heat, vermin infestation, or
atmospheres conductive to the growth of fungus
• Abnormal shock, vibration, or mechanical loading from external
• Abnormal axial or side thrust imposed on the motor shaft
2) Operation where:
• Excessive departure from rated voltage or frequency exceeding 10%
• Unbalanced Voltage between legs by more than 1%
3) Operation of speeds above the highest rated speed
4) Operation in a poorly ventilated room or an inclined position
Operation subjected to:
• Torsional impact loads
• Repetitive abnormal overloads
• Reversing or electric braking
The enclosure for the motor should be chosen to protect it from the
expected operating environment
See Chapter IV for Enclosure listings
Motors are generally mounted horizontally with feet attached to the
floor, but other arrangements are common:
- wall mounted
- ceiling mounted
- pedestal mounted
- face mounted
- flange mounted
The size and length of the shaft can be specified if the standard shaft
types or materials are not suitable for the required mounting arrangement or machine configuration
See Chapter V for table of Insulation Class information
The type of insulation used in a motor depends on the operating
temperature that the motor will experience. Motors are specified
by ambient temperature and insulation class.
Class A is an older classification. Class B is the standard for current
motor designs and class F and H are used in higher temperature
Efficiency and Economics
When selecting a motor for a particular application, both its capital cost
and the cost of energy for operation should be considered.
With today’s EISA mandates that went into affect on Dec. 19, 2010, we
have little choice in selecting the efficiency of the motor, especially if the
motor is a 140 frame motor or higher and rated over 1 HP. There are
no EISA mandates today for 1- Phase motors.
Electrical Supply Distribution System
The electrical supply distribution system must supply the correct voltage
and have sufficient capacity to start and operate the motor load.
Voltage and Frequency
Motors are available in standard voltage ranges:
Single-phase motors are rated for 120/240 volts @ 60 Hz
Three-phase motors up to 100 HP are available for 208-230/460 or
575 volts @ 60 Hz.
- 125 HP and up – 460, 575, 2400 or 4160 volts @ 60 Hz
- Other voltages and frequencies can be ordered to meet special
- Single-phase and three-phase motors are designed to operate
successfully with voltage variations of +/- 10%.
- Phase unbalance must be less than 1% for proper motor operation.
Phase unbalance leads to excessive temperature rise and a rise to
the full load amps of the motor.
- Frequency variation of up to 5% is permitted for normal motor
operation. Motor speed varies directly with the frequency of the
power supply.
Nameplate data is the critical first step in determining motor replacement.
Much of the information needed can generally be obtained from the
nameplate. Record all nameplate information; it can save time and confusion.
Important Nameplate Data
•MODEL - The ID number • DATE CODE - The month and year manufactured
•MTG. - Mounting • FRAME - The size & mounting
• PART NO. - Customer part number
• SER. - Serial number
• TYPE - Electrical type
• DES. - Code by NEMA or IEC
• PH - Electrical phase usually 1 or 3
• INS CL - Insulation Class
• DUTY - Time rating under load
• MAX AMB - The allowable surrounding air temperature
• ENCL - Enclosure (i.e. TEFC)
• RISE - The temperature rise over ambient expressed in degrees Celsius when the motor operates at nameplated HP or KW
• IP - Inherent Protection of the enclosure to solids and liquids as defined by IEC 34-5
• IC - Inherent Cooling
• CODE - NEMA locked-rotor KVA
MTH/YR MFG. - Month and year motor was manufactured
• WT/LBS - Motor weight in pounds
• WT/KG - Motor weight in kilograms
• HZ - Input frequency of the power supply, usually 50 or 60 HZ
• VOLTS - Voltage rating of the motor at the operating frequency
• HP - Rated horsepower the motor will produce
• KW - Rated output in watts
• F.L. AMPS - The rated load current expressed in amps at
nameplated horsepower with nameplate voltage and frequency
• S.F. - Percentage of the rated horsepower the motor can safely
operate at: Example: 1.15 SF (115% of rated HP)
• PF / COS - Power Factor / Cosine is the ratio of actual power to
the apparent power
• RPM - Full load speed at rated frequency
• NOM EFF - Average Efficiency
• SHAFT END BEARING - Manufacturer drive end bearing number
• OPP. END BEARING - Manufacturer opposite drive end bearing
• SHAFT END BRG - Drive end bearing size
• OPP - Opposite drive end bearing size
Major Motor Types
Alternating current (AC) induction motors are divided into two electrical
categories based on their power source – single phase and polyphase
(three phase).
AC Single Phase Types
Types of single-phase motors are distinguished mostly by the way they
are started and the torque they develop.
Shaded Pole motors have low starting torque, low cost, low efficiency,
and no capacitors. There is no start switch. These motors are used on
small direct drive fans and blowers found in homes. Shaded pole motors
should not be used to replace other types of single-phase motors.
motors have applications similar to shaded
pole, except much higher efficiency,
lower current (50% - 60% less), and higher
horsepower capability. PSC motors have a
run capacitor in the circuit at all times. They
can be used to replace shaded pole motors
for more efficient operation and can be used
for fan-on-shaft fan applications, but not for
belted fans due to the low starting torque.
Split Phase motors have moderate to low
PSC circuit diagram
starting torque (100% - 125% of full load),
high starting current, no capacitor, and a
starting switch to drop out the start winding when
the motor reaches approximately 75% of its
operating speed. They are used on easy-tostart belt drive fans and blowers, as well as
light-start pump applications.
Capacitor Start motors are designed in both moderate and high
starting torque types with both having moderate starting current, high
breakdown torques.
Cap start circuit diagram
Moderate-torque motors are used on applications in which starting
requires torques of 175% or less or on light loads such as fans, blowers,
and light-start pumps. High-torque motors have starting torques
in excess of 300% of full load and are used on compressors, industrial, commercial and farm equipment. Capacitor start motors use a
start capacitor and a start switch, which takes the capacitor and start
winding out of the circuit when motor reaches approximately 75% of its
operating speed.
Capacitor Start/Capacitor Run motors have applications and
performance similar to capacitor start except for the addition of a run
capacitor (which stays in circuit) for higher efficiency and reduced running amperage. Generally, start/ capacitor run motors are used for 3 HP
and larger single-phase applications.
On industrial duty motors,
capacitors are usually
protected by metal cases
attached to the motor
frame. This
capacitor start/capacitor
run motor has two cases.
A heavy-duty polyphase motor with cast-iron frame.
AC Polyphase (Three-Phase)
Polyphase induction motors have a
high starting torque, power factor, high
efficiency, and low current. They do not
use a switch, capacitor, relays, etc., and
are suitable for larger commercial and
industrial applications.
Polyphase induction motors are specified by their electrical design type: A,
B, C, D or E, as defined by the National
Electrical Manufacturers Association
(NEMA). These designs are suited to
particular classes of applications based upon the load requirements
typical of each class.
The table on the next page can be used to help guide which design type
to select based on application requirements.
Because of their widespread use throughout industry and because their
characteristics lend themselves to high efficiencies, many types of generalpurpose three-phase motors are required to meet mandated efficiency
levels under the U.S. Energy Policy Act. Included in the mandates are
NEMA Design B, T frame, foot-mounted motors from 1-200 HP.
Design E
Normal locked rotor
torque and current,
low slip
Design D
High locked rotor
torque and high slip
Design B
Normal locked rotor
torque and normal
locked rotor current
Design C
High locked rotor
torque and normal
locked rotor current
Rated Load Rated Load
Rated Load
Design A
High locked rotor
torque and high
locked rotor current
High peak loads with or without
flywheels such as punch presses,
shears, elevators, extractors,
winches, hoists, oil-well pumping
and wire-drawing motors
Conveyors, crushers, stirring
motors, agitators, reciprocating
pump and compressors, etc.,
where starting under load is
Medium or
Fans, blowers, centrifugal pumps
0.5-5% and compressors, motor-generator
sets, etc., where starting torque
requirements are relatively low
Medium or
Typical Applications
Fans, blowers, centrifugal pumps
0.5-5% and compressors, motor-generator
sets, etc., where starting torque
requirements are relatively low
Fans, blowers, centrifugal pumps
800-1000 0.5-3% and compressors, motor-generator
sets, etc., where starting torque
requirements are relatively low
The following table can be used to help guide which design type should be selected:
NEMA Electrical Design Standards
Direct Current (DC)
Another commonly used motor in industrial applications is the direct
current motor. It is often used in applications where adjustable speed
control is required.
Permanent magnet DC designs are generally used for motors that produce less than 5 HP. Larger horsepower applications use shunt-wound
direct current motors.
DC motors can be operated
from rectified alternating current of from low-voltage battery or generator source. This
is a low-voltage design, which
includes external connection
lugs for the input power. With
the rear endshield removed,
as in this view, the brush
assemblies and commutator
that form a DC motor’s electrical heart are clearly visible.
Both designs have linear speedtorque characteristics over the entire
speed range. SCR rated motors – those designed for use with common
solid-state speed controls – feature high starting torque for heavy load
applications and reversing capabilities, and complementary active material to compensate for the additional heating caused by the rectified AC
input. Designs are also available for use on generated low-voltage DC
power or remote applications requiring battery power.
A gearmotor is made up of an electric motor, either DC or AC, combined with a geared speed reducer.
Spur, helical or worm gears may be
used in single or multiple stages.
The configuration may be either
that of a parallel shaft, emerging
from the front of the motor, or a
right-angle shaft. Gearmotors are
often rated in input horsepower;
however, output torque, commonly
measured in inch-pounds, and output speed are the critical values.
Speed reduction
gearing is visible in this cutaway view of a
parallel-shaft gearmotor. Shown is a small,
sub-fractional horsepower gearmotor.
Gearmotors may be either integral, meaning the gear reducer and
motor share a common shaft, or they may be created from a separate
gear reducer and motor, coupled together. Integral gearmotors are
common in sub-fractional horsepower sizes; separate reducers and
motors are more often the case in fractional and integral horsepowers.
For more on gear reducers and gearmotors, see Chapter IX.
A brakemotor is a pre-connected package of industrial-duty motor and
fail-safe, stop-and-hold spring-set brake. In case of power failure, the
brake sets, holding the load in position. Brakemotors are commonly used
on hoists or other lifting devices. Brake features can also be added to standard motors through conversion kits that attach to the shaft end of either
fan-cooled or open motor.
A three-phase brakemotor. Note the
brake on the fan end. Like many brakemotors, this model has a NEMA C face
for direct mounting to the equipment
to be driven.
Motors for Precise Motion Control
These motors are always part of integrated motor-and-controller systems
that provide extreme accuracy in positioning and speed. Common applications include computer-controlled manufacturing machines and process
equipment. Servomotors are the largest category of motors for precision
motion control. AC, DC brush-type, and brushless DC versions are
available. Closed-loop control systems, common with servomotors, use
feedback devices to provide information to a digital controller, which
in turn drives the motor. In some cases, a tachometer may be used for
velocity control and an encoder for position information. In other cases,
a resolver provides both position and velocity feedback.
Step (or stepper) motors, which move in fixed increments instead of
rotating continuously, provide another means of precision motion control. Usually, they are part of open-loop control systems, meaning there
are no feedback devices.
Permanent Magnet (PMAC) Motors
The PMAC (Permanent Magnet AC) motor is traditionally of a more
complex construction than the standard induction motor. With the
new motor type, the design has been simplified by using powerful
permanent magnets to create a constant flux in the air gap, thereby
eliminating the need for the rotor windings and brushes normally used
for excitation in synchronous motors. This results in the accurate performance of a synchronous motor, combined with the robust design of a
standard induction motor. The motor is energized directly on the stator
by the variable speed drive.
Benefits of a PMAC Motor
Standard induction motors are not particularly well suited for low-speed
operation as their efficiency drops with the reduction in speed. They
may also be unable to deliver sufficiently smooth torque across the
lower speed range. This is normally overcome by using a gearbox. The
new solution provides a high torque drive coupled directly to the load.
By eliminating the gearbox, the user saves space and installation costs,
as he only needs to prepare the foundations for one piece of machinery.
This also gives more freedom in the layout design.
The PMAC motor can deliver more power from a smaller unit. For
instance, powering the in-drives of a paper machine directly at 220 to
600 r/min with a conventional induction motor would require a motor
frame substantially larger than that of a 1500 r/min motor. Using permanent magnet motors also means higher overall efficiency and less
Mechanical Considerations
Enclosures and Environment
Open Drip Proof (ODP) motors have venting
in the end frame and/or main frame, situated
to prevent drops of liquid from falling into the
motor within a 15° angle from vertical. These
motors are designed for use in areas that
are reasonably dry, clean, well-ventilated, and
usually indoors. If installed outdoors, ODP
motors should be protected with a cover that
does not restrict air flow.
Totally Enclosed Non-Ventilated (TENV) motors have no vent openings.
They are tightly enclosed to prevent the free exchange of air, but are not
air tight. TENV motors have no cooling fan and rely on convection for
cooling. They are suitable for use where exposed to dirt or dampness, but
not for hazardous locations or applications having frequent hosedowns.
Totally Enclosed Fan Cooled (TEFC) motors are
the same as TENV except they have an external
fan as an integral part of the motor to provide
cooling by blowing air over the outside frame.
Totally Enclosed Air Over motors are
specifically designed to be used within the airflow of the fan or blower they are driving. This provides an important
part of the motor’s cooling.
Totally Enclosed Hostile and Severe Environment motors are designed
for use in extremely moist or chemical environments, but not for
hazardous locations.
Explosion Proof motors meet Underwriters Laboratories or CSA standards for
use in the hazardous (explosive) locations
shown by the UL/CSA label on the motor. The
motor user must specify the explosion proof
motor required. Locations are considered
hazardous because the atmosphere contains
or may contain gas, vapor, or dust inexplosive quantities. The National Electrical Code (NEC) divides these locations into classes and groups according to the type of explosive agent.
The following list has some of the agents in each classification. For a
complete list, see Article 500 of the National Electrical Code.
Class I (Gases, Vapors)
Group A
Group B Butadiene, ethylene oxide, hydrogen,
propylene oxide
Group C Acetaldehyde, cyclopropane, diethlether,
ethylene, isoprene
Group D Acetone, acrylonitrile, ammonia, benzene,
butane, ethylene dichloride, gasoline,
hexane, methane, methanol, naphtha,
propane, propylene, styrene, toluene, vinyl
acetate, vinyl chloride, xylene
Class II (Combustible Dusts)
Group E Group F Group G
Aluminum, magnesium and other metal
dusts with similar characteristics
Carbon black, coke or coal dust
Flour, starch or grain dust
The motor ambient temperature is not to exceed +40°C or -25°C unless
the motor nameplate specifically permits another value. Marathon
Motors explosion proof motors are approved for all classes noted
except Class I, Groups A & B .
Europe - ATEX
(Category G - Gases)
North America
Europe - ATEX
(Category D - Dusts)
Class II Area Classification
(Combustible Dusts)
Group C
Group C
Group D
Group IIA, Category G - Group is not applicable to that Division or Zone, or is not defined.
¬ Group is not available from Marathon Motors.
Contact factory representative for availability.
Group D
Group IIC, Category G
Group B
Group IIB, Category G Group IIC, Category G
Group A
Group IIA, Category G Group IIB, Category G Group IIC, Category G Group IIC, Category G Group G
Group F
Group E
Category D
Group F ¬
Group G ¬
Category D
Category D
Category D
Category D
Category D
Division 2
Division 1
Zone 1
Zone 2
Zone 21
Zone 22
North America
Class I Area Classification
(Flammable Gases, Vapors or Mists)
Division 1
Group A ¬
Group B Á
Hazardous Duty Motor Area Classification Chart
Explosion Proof - Class I, Group D
(Group C as noted)
Division 1/Zone 1
Class I Area Classification
(Flammable Gases, Vapors or Mists)
Division 1/Zone 21
Class II Area Classification*
(Combustible Dusts)
Division 1 Explosion Proof/Zone 1 Flameproof
XRI® Severe Duty & IEEE-841 @ 1.15 S.F.,
Class I, Groups A,B,C,D (Sine wave power)
Division 2/Zone 2
Class I Area Classification
(Flammable Gases, Vapors or Mists)
Division 2/Zone 2 Non-Sparking
Class I, Groups A, B, C, D
ATEX compliant motors
Available through Marathon’s Mod
Central on Explosion Proof - Class I,
Group C & D @ 1.0 S.F. -
Contact Factory
ATEX compliant motors
Available through Marathon’s Mod Central on Explosion Proof Class II, Group F & G @ 1.0 S.F. Contact Factory
* Class II, Division 2 motors are not available from Marathon Motors, Zone 22 groups are not defined by ATEX.
160OC T3CT3(160)
Explosion Proof - Class I, Group D
Explosion Proof - Class II,
(Group C as noted), Sine wave Groups F & G, Sine wave
C T3BT3(165)
or PWM power
or PWM power
Available through Marathon’s Mod Central
on Totally Enclosed EPAct, XRI®, XRI® Severe
200OCT3 T3
Duty or IEEE-841 @ 1.0 S.F., Sine wave power
Class I, Groups A, B, C, D
Available through Marathon’s Mod Central
Enclosed EPAct, XRI®, XRI® Severe
215OC T2DT2(215)on Totally
or IEEE-841 @ 1.0 S.F. on PWM VFD,
280OC T2AT2(280)
260OC T2BT2(260)
Hazardous Duty Motor Temperature Code Chart
NEMA Frame/Shaft Sizes
Frame numbers are not intended to indicate electrical characteristics
such as horsepower. However, as a frame number becomes higher so in
general does the physical size of the motor and the horsepower. There
are many motors of the same horsepower built in different frames.
NEMA (National Electrical Manufacturers Association) frame size refers
to mounting only and has no direct bearing on the motor body diameter.
In any standard frame number designation there are either two or three
numbers. Typical examples are frame numbers 48, 56, 145, and 215.
The frame number relates to the “D” dimension (distance from center
of shaft to center bottom of mount). For example, in the two-digit 56
frame, the “D” dimension is 31/2”, 56 divided by 16 = 31/2”. For the
“D” dimension of a three-digit frame number, consider only the first two
digits and use the divisor 4. In frame number 145, for example, the first
two digits divided by the constant 4 is equal to the “D” dimension. 14
divided by 4 = 31/2”. Similarly, the “D” dimension of a 213 frame motor
is 51/4”, 21 divided by 4 = 51/4”.
By NEMA definition, two-digit frame numbers are fractional frames even
though 1 HP or larger motors may be built in them. Three-digit frame
numbers are by definition integral frames. The third numeral indicates
the distance between the mounting holes parallel to the base. It has no
significance in a footless motor.
A summary of NEMA standard dimensions is on the facing page.
Shaded area denotes dimensions established by NEMA standard MG-1. Other dimensions will vary among
Motor Frame Dimensions
NEMA Frame Suffixes
= NEMA C face mounting (specify with or without rigid base)
= NEMA D flange mounting (specify with or without
rigid base)
= Indicates a frame with a rigid base having an F dimension larger than that of the same frame without the suffix H. For example, combination 56H base motors have mounting holes for NEMA 56 and NEMA 143-5T and a standard NEMA 56 shaft
= NEMA C face, threaded shaft pump motor
JM = Close-coupled pump motor with specific dimensions and
JP = Close-coupled pump motor with specific dimensions and
M =6 / ” flange (oil burner)
N =7 / ” flange (oil burner)
T,TS = Integral horsepower NEMA standard shaft dimensions if no additional letters follow the “T” or “TS”.
TS = Motor with NEMA standard “short shaft” for belt driven loads.
= Non-NEMA standard mount; a drawing is required to be sure of dimensions. Can indicate a special base, face or flange.
= Non-NEMA standard shaft; a drawing is required to be sure of dimensions.
Frame Prefixes
Letters or numbers appearing in front of the NEMA frame number are
those of the manufacturer. They have no NEMA frame significance. The
significance from one manufacturer to another will vary.
Unless specified otherwise, motors can be mounted in any position
or any angle. However, unless a drip cover is used for shaft-up or
shaft-down applications, drip proof motors must be mounted in the
horizontal or sidewall position to meet the enclosure definition. Mount
motor securely to the mounting base of equipment or to a rigid, flat
surface, preferably metallic.
Types of Mounts
Rigid base is bolted, welded, or cast on main
frame and allows motor to be rigidly mounted
on equipment.
Resilient base has isolation or resilient rings
between motor mounting hubs and base to
absorb vibrations and noise. A conductor is
imbedded in the ring to complete the circuit for
grounding purposes.
NEMA C face mount is a machined face with
a pilot on the shaft end which allows direct
mounting with the pump or other direct coupled equipment. Bolts pass through mounted
part to threaded hole in the motor face.
NEMA D flange mount is a machined flange
with rabbet for mountings. Bolts pass through
motor flange to a threaded hole in the mounted
part. NEMA C face motors are by far the most
popular and most readily available. NEMA D
flange kits are stocked by some manufacturers,
including Marathon Motors.
Type M or N mount has special flange for
direct attachment to fuel atomizing pump on an
oil burner. In recent years, this type of mounting has become widely used on auger drives in
poultry feeders.
Extended through-bolt motors have bolts protruding from the front or rear of the motor by
which it is mounted. This is usually used on small
direct drive fans or blowers.
Application Mounting
For direct-coupled applications, align shaft and coupling carefully, using
shims as required under motor base. Use a flexible coupling, if possible,
but not as a substitute for good alignment practices.
Pulleys, sheaves, sprockets and gears should be generally mounted as
close as possible to the bearing on the motor shaft, thereby lessening
the bearing load.
The center point of the belt, or system of V-belts, should not be beyond
the end of the motor shaft.
The inner edge of the sheave or pulley rim should not be closer to the
bearing than the shoulder on the shaft, but should be as close to this
point as possible.
The outer edge of a chain sprocket or gear should not extend beyond
the end of the motor shaft.
To obtain the minimum pitch diameters for the flat-belt, timing-belt,
chain and gear drives, the multiplier given in the following table should
be applied to the narrow V-belt sheave pitch diameters in NEMA MG
1-14.444 for alternating current, general-purpose motors, or to the
V-belt sheave pitch diameters as determined from NEMA MG 1-14.67
for industrial direct current motors.
Flat belt*
Timing belt†
Chain sprocket
Spur Gear
Helical gear
* This multiplier is intended for use with conventional single-ply flat
belts. When other than single-ply belts are used, the use of a larger
multiplier is recommended.
† It is often necessary to install timing belts with a snug fit. However,
tension should be no more than what is necessary to avoid belt slap or
tooth jumping.
Motor Guidelines for Belted Applications
The information contained in this document is intended to be used for
applications where Marathon Motors motors are connected to other
equipment through the use of a V-belt drive. These are to be used as
guidelines only since Marathon Motors does not warrant the complete
drive system.
The goal of any belted system is to efficiently transmit the required
torque while minimizing the loads on the bearings and shafts of the
motor and driven equipment. This can be accomplished by following
these four basic guidelines:
Use the largest practical sheave diameter.
Use the fewest number of belts possible.
Keep sheaves as close as possible to support bearings.
Tension the belts to the lowest tension that will still transmit the
required torque without slipping.
1. Sheave Diameter Guidelines
In general, smaller sheaves produce greater shaft stress and shaft
deflection due to increased belt tension. See Table 1 for minimum
recommended sheave diameters. Using larger sheaves increases the
contact with belts which reduces the number of belts required. It also
increases the belt speed, resulting in higher system efficiencies. When
selecting sheaves, do not exceed the manufacturer’s recommended
maximum rim speed. Typically 6,500 feet per minute for cast iron
sheaves, 8,000 feet per minute for ductile iron and 10,000 feet per
minute for steel. The following formula will determine sheave rim speed:
Shaft RPM x 3.14 x Sheave Dia. in inches
2. Number of Belts
In general, use the fewest number of belts that will transmit the required
torque without slipping. See Table 1 for maximum recommended
number of belts. Each belt adds to the tension in the system which
increases load on the shafts and bearings. Belts are most efficient when
operated at or near their rated horsepower.
If the sheaves have more grooves than the number of belts required, use
the grooves closest to the motor.
3. Sheave Location
Install sheaves as close to the housings as possible to increase the
bearing life of the motor and driven equipment.
4. Belt Tension
In general, belt tensions are to be kept as loose as possible while still
transmitting the required torque without slipping. Belt tensions must be
measured with a belt tension gage. These inexpensive gages may be
obtained through belt manufacturers, or distributors.
Proper belt tension is determined by measuring the required force to
deflect the center of the belt at a given distance. See Fig. 3. The proper
deflection (in inches) is determined by dividing the belt span in inches
by 64. Calculate the proper deflection and then see Table 1 for the
required belt deflected force to achieve the calculated deflection.
After tensioning the belt, rotate the sheaves for several rotations or start
the system and run for a few minutes if possible to seat belts into the
grooves, then re-tension the belts.
Belt tensioning by feel is NOT acceptable. Tensioning by “feel” can be
very misleading, and can damage equipment. New belts will stretch
during use, and should be retensioned after the first eight hours of use.
Table 1: Recommended Sheave Diameters, Belt Type and Number of Belts
1200 rpm1800 rpm3600 rpm
Min.Max. Belt Min.Max. Belt Min.Max.Belt
Sheave Belt # DeflectedSheaveBelt # DeflectedSheaveBelt # Deflected
Hp Dia. (in.) Type
Dia. (in.) Type
Dia. (in.) Type
0.752.2 3VX 1
3.4 2.23VX 1
2.2 2.23VX 1 1.3
1 2.4 3VX 1
4.0 2.23VX 1
3.1 2.23VX 1 1.6
1.52.4 3VX 2
3.1 2.43VX 2
2.1 2.23VX 1 2.5
2 2.4 3VX 3
2.8 2.43VX 2
2.9 2.43VX 1 2.7
3 3.0 3VX 2
2.9 2.43VX 3
2.9 2.43VX 2 2.3
5 3.0 3VX 3
4.0 3.03VX 3
3.7 2.43VX 3 2.5
7.53.8 3VX 4
4.7 3.03VX 4
4.1 3.03VX 2 4.2
10 4.4 3VX 4
5.4 3.83VX 4
4.3 3.03VX 3 3.8
15 4.4 3VX 5
5.4 4.43VX 4
5.4 3.83VX 3 4.4
20 5.2 3VX 6
6.0 4.43VX 6
4.8 4.43VX 3 5.0
25 6.0 3VX 7
5.6 4.43VX 7
5.2 4.43VX 4 4.7
In general, 3600 RPM motors 30 HP and
40 6.8 5VX 4
6.0 3VX
larger are not belted due to bearing
50 8.2 5VX 4
6.8 3VX
speed-load limitation.
60 8.2 5VX 5
7.4 5VX
NEMA sheave sizes
Above - NEMA Sheave sizes
5V/8V 11 / 7
14 / 24
5V/8V 12 / 7
14 / 26
5V/8V 13 / 8
15 / 26
5V/8V 14 / 9
15 / 25
Exceeds cast iron sheave rim speed –
5V/8V 15 / 9
15 / 27
special sheave material required
1. Horsepowers are nameplate motor horsepowers, and RPMs are
motor (driver) speeds.
2. NEMA minimum sheave diameters are from NEMA MG 1, Part 14,
Table 14-1.
3. Consult Marathon Motors for applications utilizing (1) smaller
sheaves and/or more belts than specified (2) variable speed applications (3) values outside these recommendations.
4. Selections are based on a 1.4 service factor, 5 to 1 speed ratio
and various Power Transmission Manufacturer’s catalogs used as
5. These selections are for Narrow V-belt sections only. Consult
Marathon Motors for details on conventional V-belt sections (A, B,
C, D and E), or other belt types.
6. Belt deflected force is per section 4 of this document and is the
average force required to deflect the center of a belt 1/64 of the
belt span distance. Tolerance on this force is ± 0.5 lbf. for forces 6
lbs, and ± 2 lbf. for forces > 6 lbs.
Electrical Characteristics and Connections
Voltage, frequency and phase of power supply should be consistent
with the motor nameplate rating. A motor will operate satisfactorily
on voltage within 10% of nameplate value, or frequency within 5%, or
combined voltage and frequency variation not to exceed 10%.
Common 60 hz voltages for single-phase motors are 115 volt, 230 volt,
and 115/230 volt.
Common 60 hz voltage for three-phase motors are 230 volt, 460 volt
and 230/460 volt. Two hundred volt and 575 volt motors are sometimes
encountered. In prior NEMA standards these voltages were listed as 208
or 220/440 or 550 volts. Motors with these voltages on the nameplate
can safely be replaced by motors having the current standard markings
of 200 or 208, 230/460 or 575 volts, respectively.
Motors rated 115/208-230 volt and 208-230/460 volt, in most cases,
will operate satisfactorily at 208 volts, but the torque will be 20% - 25%
lower. Operating below 208 volts may require a 208 volt (or 200 volt)
motor or the use of the next higher horsepower, standard voltage
Single-phase motors account for up to 80% of the motors used in the
United States but are used mostly in homes and in auxiliary low-horsepower industrial applications such as fans and on farms.
Three-phase motors are generally used on larger commercial and
industrial equipment.
Current (Amps)
In comparing motor types, the full load amps and/or service factor amps
are key parameters for determining the proper loading on the motor.
For example, never replace a PSC type motor with a shaded pole type
as the latter’s amps will normally be 50% - 60% higher. Compare PSC
with PSC, capacitor start with capacitor start, and so forth.
Hertz / Frequency
In North America 60 hz (cycles) is the common power source. However,
most of the rest of the world is supplied with 50 hz power.
Exactly 746 watts of electrical power will produce 1 HP if a motor could
operate at 100% efficiency, but of course no motor is 100% efficient. A 1
HP motor operating at 84% efficiency will have a total watt consumption
of 888 watts. This amounts to 746 watts of usable power and 142 watts
loss due to heat, friction, etc. (888 x .84 = 746 = 1 HP).
Horsepower can also be calculated if torque is known, using one of
these formulas:
Torque (lb-ft) x RPM
HP = 5,250
Torque (oz-ft) x RPM
HP = Torque (lb-in) x RPM
HP = Speeds
The approximate RPM at rated load for small and medium motors operating at 60 hz and 50 hz at rated volts are as follows:
60 hz
50 hz
Synch. Speed
2 Pole345028503600
4 Pole172514251800
6 Pole
8 Pole
Synchronous speed (no-load) can be determined by this formula:
Frequency (Hertz) x 120
Number of Poles
Insulation Class
Insulation systems are rated by standard NEMA classifications according
to maximum allowable operating temperatures. They are as follows:
Maximum Allowed Temperature*
* Motor temperature rise plus maximum ambient
Generally, replace a motor with one having an equal or higher insulation
class. Replacement with one of lower temperature rating could result in
premature failure of the motor. Each 10°C rise above these ratings can
reduce the motor’s service life by one half.
Service Factor
The service factor (SF) is a measure of continuous overload capacity at
which a motor can operate without overload or damage, provided the
other design parameters such as rated voltage, frequency and ambient
temperature are within norms. Example: a 3/4 HP motor with a 1.15 SF
can operate at .86 HP, (.75 HP x 1.15 = .862 HP) without overheating
or otherwise damaging the motor if rated voltage and frequency are
supplied at the motor’s leads. Some motors, including most Marathon
Motors motors, have higher service factors than the NEMA standard.
It is not uncommon for the original equipment manufacturer (OEM)
to load the motor to its maximum load capability (service factor). For
this reason, do not replace a motor with one of the same nameplate
horsepower but with a lower service factor. Always make certain that
the replacement motor has a maximum HP rating (rated HP x SF) equal
to or higher than that which it replaces. Multiply the horsepower by the
service factor for maximum potential loading.
For easy reference, standard NEMA service factors for various horsepower motors and motor speeds are shown in this table.
Service Factor Synchronous Speed (RPM)
1/6, 1/4, 1/3
1-1/2 up
1.35 1.35
1.25 1.25
1.15 1.15
1.15 1.15
The NEMA service factor for totally enclosed motors is 1.0. However, many manufacturers build TEFC with a 1.15 service factor.
Capacitors are used on all fractional HP induction motors except shadedpole, split-phase and polyphase. Start capacitors are designed to stay
in circuit a very short time (3-5 seconds), while run capacitors are permanently in circuit. Capacitors are rated by capacity and voltage. Never
use a capacitor with a voltage less than that recommended with the
replacement motor. A higher voltage is acceptable.
A motor’s efficiency is a measurement of useful work produced by the
motor versus the energy it consumes (heat and friction). An 84% efficient
motor with a total watt draw of 400W produces 336 watts of useful
energy (400 x .84 = 336W). The 64 watts lost (400 - 336 = 64W) becomes
Encoders are devices that translate a signal, whether motion into position or velocity feedback for a motion control system. Take a conveyor
system as an application. You want to run the conveyor at 100 feet per
minute. The motor that powers this conveyor has an encoder mounted
to its shaft. Output from the encoder goes into the controller and as
long as the output signal is telling the controller that everything is fine
– the motor is running at the correct speed - it continues running at
the current speed. If the load on the conveyor changes, like it is being
overloaded due to additional weight of product added to the conveyor,
the controller should notice a change in pulses from the encoder, for the
speed of the conveyor slows down from this additional weight, and the
controller will send a signal to the motor to speed up to compensate
for this load change. Once the load has been returned to the standard
expected load, the control will again see a signal from the encoder and
will slow the motor down to the needed speed.
There are two main types of Encoders, Rotary and Linear and each type
can use different sensing technologies. They include Optical, Magnetic
or Inductive. Optical Rotary encoders are the most common type used.
Thermal Protection (Overload)
A thermal protector, automatic or manual, mounted in the end frame
or on a winding, is designed to prevent a motor from getting too hot,
causing possible fire or damage to the motor. Protectors are generally
current- and temperature-sensitive. Some motors have no inherent
protector, but they should have protection provided in the overall system’s design for safety. Never bypass a protector because of nuisance
tripping. This is generally an indication of some other problem, such as
overloading or lack of proper ventilation.
Never replace nor choose an automatic-reset thermal overload protected motor for an application where the driven load could cause
personal injury if the motor should restart unexpectedly. Only manualreset thermal overloads should be used in such applications.
Basic types of overload protectors include:
Automatic Reset: After the motor cools, this line-interrupting protector automatically restores power. It should not be used where
unexpected restarting would be hazardous.
Manual Reset: This line-interrupting protector has an external button
that must be pushed to restore power to the motor. Use where
unexpected restarting would be hazardous, as on saws, conveyors,
compressors and other machinery.
Resistance Temperature Detectors: Precision-calibrated resistors
are mounted in the motor and are used in conjunction with an instrument supplied by the customer to detect high temperatures.
Shaft Grounding Devices
Shaft grounding is recommended (NEMA MG1 as an effective
means of bearing protection for motors operated from inverter power.
Shaft voltage occurs in motors powered by variable frequency inverters
(VFD) These VFDs induce shaft voltages onto the shaft of the driven motor
because of the extremely high speed switching of the insulated gate bipolar transistors (IGBTs) which produce the pulse width modulation used
to control AC motors. The presence of high frequency ground currents
can cause sparks, arcing and electrical shocks and can damage bearings.
One grounding device is adequate to bleed down inverter-sourced shaft
voltages, thereby protecting both bearings for motors as large as 6085
There are four common techniques that can minimize or eliminate this
bearing damage caused by these ground currents” Faraday shield, insulated bearings or ceramic bearings, a ground brush or a grounding ring.
Shielding the cable or wire between the motor and the VFD can also
significantly improve these spikes as well.
Faraday Shield:
An electrostatic shielded induction motor (ESIM) is one approach to the
shaft-voltage problem, as the insulation reduces voltage levels below
the dielectric breakdown. This effectively stops bearing degradation
and offers one solution to accelerated bearing wear caused by fluting,
induced by VFDs.
Grounding Brush:
Grounding the shaft by installing a grounding device provides an alternate low-impedance path from the motor shaft to the motor case. This
channels the current away from the bearings. It significantly reduces
shaft voltage, and therefore bearing current, by no allowing voltage to
build up on the rotor.
Shaft Grounding Ring:
A shaft grounding ring (SGR) is similar to a grounding brush, except
that this brush makes use of conductive micro fibers, creating a low impedance path from the motor.
Insulated Bearings:
Insulated or ceramic bearings eliminate the path to ground through the
bearing for current to flow.
Torque-speed Characteristics of Motors:
The amount of torque produced by a motor generally varies with
This Torque-Speed characteristic depends on the type and design
of a motor, and is often shown on a Torque-Speed graph.
Figure 2.2
Typical Torque-Speed Graph
• Some important factors indicated by the graph include:
(a) Starting torque - the torque produced at zero speed;
(b)Pull-up torque - the minimum torque produced during acceleration
from standstill to operating speed;
(c)Breakdown torque - the maximum torque that the motor can produce before stalling.
anual Reset: This line-interrupting protector has an
xternal button that must be pushed to restore power to
e motor. Use where unexpected restarting would be
azardous, Individual
as on saws, conveyors,
Circuit Wiring
her machinery.
varies with the frequency of the pulses introduc
output voltage.
Pulse width modulated AC drives offer an extr
speed range, a host of control functions includin
mable acceleration and deceleration ramps and
set speeds,
efficiency and, in m
All wiring and
connections should
with energy
the National
esistance Temperature
and practices.
torque precision
equal to or closely a
sistors areElectrical
mounted inCode
the motor
and are
in con(NEC)
local codes
that of a DC system. Perhaps the major reas
nction withwire
an instrument
by theand
the motor
the power
will limit the starting and
growing popularity, however, is their ability to wo
etect high temperatures.
load carrying abilities of the motor. The recommended
wire and
wide range of AC induction
available for in
transformer sizes are shown in the following
ally atcharts.
a price competitive with that of a DC driv
(Refer to Section G for Inverter capabilities o
Single Phase Motors - 230 Volts
Single Phase Motors – 230 Volts
Chart 1
GENERAL • Electrical/Connec
Chart 2
Three Phase Motors - 230 & 460 Volts
Motor Starters
As their name implies, motor starters apply electric power to a motor to
begin its operation. They also remove power to stop the motor. Beyond
merely switching power on and off, starters include overload protection,
as required by the National Electrical Code. The code also usually requires
a disconnect and short circuit protection on motor branch circuits.
Fused disconnects and circuit breakers provide this and are often
incorporated into a motor starter enclosure, resulting in a unit referred
to as a combination starter.
Across The Line Starting of Induction Motors
An across the line starter is the least expensive option and is usually
used for induction motors.
All NEMA design induction motors up to 200 HP, and many larger
ones, can withstand full voltage starts.
Manual starters are often used for smaller motors - up to about 10 HP.
They consist of a switch with one set of contacts for each phase and
a thermal overload device. The starter contacts remain closed if
power is removed from the circuit and the motor restarts when
power is reapplied.
Manually Operated
Figure 4.1
Manual Starter
Magnetic Starters
Magnetic starters are used with larger motors or where greater control
is desired. The main element of the starter is the contactor, which is a
set of contacts operated by an electromagnetic coil. Energizing the coil
causes the contacts A to close, allowing large currents to be initiated
and interrupted by a control signal. The control voltage need not
be the same as the motor supply voltage, and is often low voltage
allowing the start and stop controls to be located away from the
power circuit.
Contacts Operated
by Contactor Coil
Figure 4.2
Magnetic Starter
Closing the starter button contacts energizes the contactor coil. An
auxiliary contact, B, on the contactor is wired to seal in the coil circuit. The contactor de-energizes if the control circuit is interrupted
by operating the stop button or if power is lost.
The overload contacts are arranged so an overload trip on any
phase will cause all phases to open.
Contactors are rated for various operating voltages and are sized
according to motor HP and type of duty expected.
Reduced Voltage Starters
If the driven load or the power distribution system cannot accept a
full voltage start, some type of reduced voltage or “soft” starting
scheme must be used.
Typical reduced voltage starters are: primary resistance starters,
autotransformers, part winding starters, wye-delta and solid state
These devices can only be used where low starting torque is
Primary Resistance Starters
Closing the contacts at A connects the motor to the supply via
resistors which provide a voltage drop to reduce the starting
voltage available to the motor.
The resistor’s value is chosen to provide adequate starting torque
while minimizing starting current.
Motor inrush current declines during acceleration, reducing the
voltage drop across the resistors and providing more motor torque.
This results in smooth acceleration.
After a set period of time, contacts A open and the resistors are
shorted out by contacts B, applying full voltage to the motor.
Figure 4.3
Primary Resistance Starter
Autotransformer Starters
An autotranformer is a single winding transformer on a laminiated
core with taps at various points on the winding. The taps are usually
expressed as a percentage of the total number of turns and thus
percentage of applied voltage output.
Three autotransformers are connected in a wye configuration or
two in an open delta configuration, with taps selected to provide
adequate starting current.
The motor is first energized at a reduced voltage by closing contacts
Figure 4.4
Autotransformer Starter
After a short time, the autotransformers are switched out of the
circuit by opening contacts A and closing contacts B, thus applying
full voltage to the motor.
Athe autotransformers need not have high capacity as they are only
used for a very short period of time.
Wye-Delta Starting
Wye-Delta Starting can be used with motors where all six leads of
the stator winding are available (on some motors only three leads
are accessible).
Motor windings
Figure 4.5
Wye-Delta Starter
By first closing contacts A and B, the windings are connected in
a wye configuration which presents 57% of rated voltage to the
Full voltage is then applied by reconnecting the motor in a delta
configuration by closing contacts C and opening those at A.
The starting current and torque are 33% of their full voltage ratings,
limiting applications to loads requiring very low starting torque.
Part Winding Starters
Part winding starters are sometimes used on motors wound for dual
voltage operation such as a 230/460 V motor. These motors have
two sets of winding connected in parallel for low voltage, and in
series for high voltage operation.
When used on the lower voltage, they can be started by first energizing
only one winding, limiting starting current and torque to approximately one half of the full voltage values.
The second winding is then connected normally once the motor
nears operating speed.
Reading a Marathon Motors Model Number
There is no independently established standard for setting up a motor’s
model number, but the procedure is typically tied to descriptions of
various electrical and mechanical features. While other manufacturers
use other designations, here is how Marathon Motors model numbers
are configured.
Example (For Fractional): 1PC48C17D2000AP
This is a breakdown of the model on the nameplate:
48 C 17
D 2000 A
1 2 3 4 5 6 7 101112
This is a breakdown of the model in the catalog:
48 C 17 D2000
4 5 6 710
Example (For Integral): 2QA215TBDRA7076ALL
This is a breakdown of the model on the nameplate:
A 215T B
A 7076 AL
1 2 3 4 5 7 8 9 101112
This is a breakdown of the model in the catalog:
215TB D R A7076
4 5 7 8 910
1. Date Code - Year of Manufacture
(Not shown in catalog listings.)
2. Thermal Protection (Not shown in catalog listings.)
UL Recognized
Motor Protector
Automatic Reset
Manual Reset
Automatic Reset
Manual Reset
UL Recognized
Automatic Reset
Manual Reset
# Motor protector combination is U.L. recognized only if motor is used in
direct drive fan duty application, and is under locked rotor condition, or is
running under no-load condition.
3. Date Code - Month of Manufacturer (Not shown in catalog listings.)
4. NEMA Frame Size - (Integral motors - T and U designate standard shaft, TS
and US designate short shaft)
5. Electrical Type
Single Phase:
A=Permanent split capacitor
B=Capacitor start, capacitor run
C=Capacitor start, induction run
N=Split phase start, capacitor run
S= Split phase
Three Phase:
T= Three phase
H=Inverter Duty/IEEE841 Inverter Duty
V= Medium Voltage
DC Power:
E=Permanent Magnet DC
6. RPM or Speed at 60 Hz (Fractional Only)
34=2-Pole, 3600 rpm
17=4-Pole, 1800 rpm
11=6-Pole, 1200 rpm
8=8-Pole, 900 rpm
E=Explosion proof, non-ventilated
F =Totally enclosed, fan cooled
G=Explosion proof, fan cooled
O = Open
P = Partial
S = Semi-enclosed
T=Totally enclosed, non-ventilated
V=Washdown, non-ventilated
W=Washdown, fan cooled
8. Frame Construction
L= Aluminum (Full Frame)
Y = Aluminum (Full Frame)
Z = Aluminum (High Mount Down Frame)
= Rolled Steel - Sourced
D = Stainless Steel - Sourced
U=Frameless - Sourced
H = Aluminum - Sourced
R = Rolled Steel (Full Frame)
W = Rolled Steel (Full Frame)
X = Rolled Steel (High Mount Down Frame)
B = Rolled Steel - Sourced
S = Cast Iron (Full Frame)
N = Cast Iron (Full Frame)
P = Cast Iron (High Mount Down Frame)
C = Cast Iron - Sourced
D = Stainless Steel
9. Style Letter (A, B, C, etc. indicate redesign)
10.Sequence Number
11.Minor Modification Letter(s)
Fractional - 1 letter; Integral - 2 letters
12.Manufacturing Code - A code for the factory where
the motor was manufactured.
Example (“harmonized” motor design):
5KH3 6 K G142– X
A. Rotating Device
Type of Winding
KH - Split Phase
KC - Capacitor Start, Induction Run
K - Polyphase
KCP - Permanent Split Capacitor
KCR - Capacitor Start, Capacitor Run
C. Lamination Size
3 - 48 frame, 4 - 56 frame
D. Length of Frame
48 frame
5.17 3 5.42
4 None
5 5.80
6 6.23
7 6.63
8 7.23
9 Spec.
56 frame
Stack Length
D-1.0” J-1-5/8”
E-1-1/8” K-1-3/4”
L-1-7/8” M-2.0”
P-2-1/2” R-2-3/4”
S- 3.0”
T- 3-1/4”
U- 3-1/2”
Q- Spec.
F. Endshield Construction
G & N - Aluminum
K - Steel
C - Cap/Can
G. Sequence Number
H. Current Revision (blank if original)
Type of Overload
X - UL Auto running & locked rotor
Y - UL Manual running & locked rotor
S - UL Auto locked rotor
T - Non-UL Auto running & locked rotor
U - Non-UL Manual running & locked rotor
V- Thermostat
W - UL Motor Parts
Major Components o
Rear Endshield
Fan Guard**
of an Electric Motor
Capacitor Case*
Internal Fan
Front Endshield
Cast Rotor
End Ring
Metric (IEC) Designations and Dimensions
The International Electrotechnical Commission (IEC) is a European-based
organization that publishes and promotes worldwide mechanical and
electrical standards for motors, among other things. In simple terms,
it can be said that IEC is the international counterpart to the National
Electrical Manufacturers Association (NEMA), which publishes the motor
standards most commonly used throughout North America.
Dimensionally, IEC standards are expressed in metric units.
IEC / NEMA Dimensional Comparison
* Shaft dimensions of these IEC frames may vary between manufacturers.
**Horsepower listed is closest comparable rating with similar mounting
dimensions. In some instances, this results in a greater HP rating than
required. For example, 37 kW 4 pole converts to 50 HP but nearest
HP rating in the NEMA frame having comparable dimensions is 75 HP.
OBSERVE CAUTION if the drive train or driven load is likely to be
damaged by the greater HP.
Equivalent HP can be calculated by multiplying the kW rating by 1.341.
Multiply HP by .7457 to convert HP of kW.
To convert from millimeters to inches multiply by .03937.
To convert from inches to millimeters multiply by 25.
KW/HP** Frame
Dimensions in Millimeters
3 Phase – TEFC
2 Pole 4 Pole 6 Pole
35.5 5.8
NA– – ––– – –– ––
63 635040 7114023
NA – – – – – – –1/3HP
71 715645 7144530.55.37–
80 62.5 50 10 19
40 1.1 .75 .55KW
48 76.2 54 34.9 8.7 12.7 63.5 38.11-1/2 1 3/4HP
90S 907050102456501.51.1.75
56 88.961.938.1 8.715.969.947.6 2 1-1/2 1
90L 907062.5
56 88.969.850.8 8.722.257.257.2 3 2 1-1/2
100L 100807012286360 3 2.21.5
145T88.969.863.5 8.722.257.257.2 4 3 2
112L 1129557122870603.72.21.5
182T114.3 95.2 57.2 10.7 28 70 69.9 5
112M 1129570122870603.7 42.2
184T114.3 95.2 68.2 10.7 28 70 69.9 5 5-4/5 –
132S 13210870 1238 89 807.55.5 3
213T133.4 108 69.8 10.7 34.9 89 85.7 10 7-1/2 –
215T133.4 108 88.8 10.7 34.9 89 85.7
10 7-1/2
160M* 160127105 15 42 108110 15 11 7.5
254T158.8127104.813.541.3 108101.6 20 15 10
160L* 160127127 15 42 10811018.5 15 11
256T158.8127 12713.541.3 108101.525 20 15
139.5 120.5
284T 177.8139.8120.2 13.5 47.6 121 117.5 –
180 139.5 139.5 15
286T 177.8139.8139.8 13.5 47.6 121 117.5 30
324T 203.3158.8133.4 16.7 54
133 133.4 40
159 152.5 19
326T 203.2158.8152.4 16.7 54
133 133.4 50
225S* 225178143 19 60 149140 – 37 30
364T 228.6117.8142.8 16.7 60.3 149 149.2 – 50/75 40
365 228.6 177.8 155.6 16.7 60.3 149 149.260/7560/75 50
405T 254 203.2174.6 20.6 73
168 182.275/10075/100–
280 228.5 184
444T 279.4228.6184.2 20.6 85.7 190 215.9 –
– 60/100
228.5 209.5
445T 279.4228.6209.6 20.6 85.7 190 215.9 –
– 75/125
See notes on facing page.
IEC Enclosure Protection Indexes
Like NEMA, IEC has designations indicating the protection provided by
a motor’s enclosure. However, where NEMA designations are in words,
such as Open Drip Proof or Totally Enclosed Fan Cooled, IEC uses a
two-digit Index of Protection (IP) designation. The first digit indicates
how well-protected the motor is against the entry of solid objects; the
second digit refers to water entry.
By way of general comparison, an IP 23 motor relates to Open Drip
Proof, IP 44 to totally enclosed.
Marathon Motors stock General Purpose, ODP, motors are typically
rated at IP23 and our TEFC, General Purpose, motors are typically listed
as IP43 or IP54.
Protection Against
Solid Objects
No. Definition
Protection Against
No. Definition
0 No protection.
No protection.
1 Protected against solid objects
1 Protected against water
of over 50mm (e.g. accidental
vertically dripping
hand contact). (condensation).
2 Protected against solid objects
of over 12mm (e.g. finger).
Protected against water dripping
up to 15° from the vertical.
3 Protected against solid objects 3
of over 2.5mm (e.g. tools, wire).
Protected against rain falling
at up to 60° from the vertical.
4 Protected against solid objects 4
of over 1mm (e.g. thin wire).
Protected against water splashes
from all directions.
5 Protected against dust.
Protected against jets of water
from all directions.
6 Totally protected against dust. 6 Protected against jets of water
Does not involve rotating comparable to heavy seas.
Protected against the effects of
immersion to depths of between
0.15 and 1m.
Protected against the effects of
prolonged immersion at depth.
IEC Cooling, Insulation and Duty Cycle Indexes
IEC has additional designations indicating how a motor is cooled (twodigit IC codes). For most practical purposes, IC 01 relates to a NEMA
open design, IC 40 to Totally Enclosed Non-Ventilated (TENV), IC 41 to
Totally Enclosed Fan Cooled (TEFC), and IC 48 to Totally Enclosed Air
Over (TEAO).
IEC winding insulation classes parallel those of NEMA and in all but very
rare cases use the same letter designations.
Duty cycles are, however, different.
Where NEMA commonly
designates either continuous, intermittent, or special duty (typically
expressed in minutes), IEC uses eight duty cycle designations.
S1Continuous duty. The motor works at a constant load for
enough time to reach temperature equilibrium.
S2 Short-time duty. The motor works at a constant load, but not
long enough to reach temperature equilibrium, and the rest
periods are long enough for the motor to reach ambient temperature.
S3 Intermittent periodic duty. Sequential, identical run and rest
cycles with constant load. Temperature equilibrium is never
reached. Starting current has little effect on temperature rise.
S4 Intermittent periodic duty with starting. Sequential, identical
start, run and rest cycles with constant load. Temperature equilibrium is not reached, but starting current affects temperature
S5 Intermittent periodic duty with electric braking. Sequential,
identical cycles of starting, running at constant load, electric
braking, and rest. Temperature equilibrium is not reached.
S6 Continuous operation with intermittent load. Sequential, identical cycles of running with constant load and running with no
load. No rest periods.
S7 Continuous operation with electric braking. Sequential identical
cycles of starting, running at constant load and electric braking.
No rest periods.
S8 Continuous operation with periodic changes in load and speed.
Sequential, identical duty cycles of start, run at constant load
and given speed, then run at other constant loads and speeds.
No rest periods.
IEC Design Types
The electrical performance characteristics of IEC Design N motors in
general mirror those of NEMA Design B – the most common type of motor
for industrial applications. By the same token, the characteristics of IEC
Design H are nearly identical to those of NEMA Design C. There is no
specific IEC equivalent to NEMA Design D. (See chart on Page 13 for
characteristics of NEMA design types.)
IEC Mounting Designations
Three common IEC mounting options are shown in this photo. From left, a B5
flange, B14 face and rigid B3 base. In this case, any of the options can be bolted
to a modularly designed round-body IEC 71 frame motor.
Motor Maintenance
Motors, properly selected and installed, are capable of operating for
many years with a reasonably small amount of maintenance.
Before servicing a motor and motor-operated equipment, disconnect
the power supply from motors and accessories. Use safe working practices during servicing of the equipment.
Clean motor surfaces and ventilation openings periodically, preferably
with a vacuum cleaner. Heavy accumulations of dust and lint will result
in overheating and premature motor failure.
Lubrication Procedure
Motors 10 HP and smaller are usually lubricated at the factory to operate
for long periods under normal service conditions without re-lubrication.
Excessive or too frequent lubrication may actually damage the motor.
Follow instructions furnished with the motor, usually on the nameplate
or terminal box cover or on a separate instruction. If instructions are
not available, re-lubricate according to the chart on the next page. Use
high-quality ball bearing grease. Grease consistency should be suitable
for the motor’s insulation class. For Class B, F or H, use a medium consistency polyurea grease such as EXXON POLYREX® EM.
If the motor is equipped with lubrication fitting, clean the fitting tip, and
apply grease gun. Use one to two full strokes on NEMA 215 frame and
smaller motors. Use two to three strokes on NEMA 254 through NEMA
365 frame. Use three to four strokes on NEMA 404 frames and larger.
For motors that have grease drain plugs, remove the plugs and operate
the motor for 20 minutes before replacing the plugs.
For motors equipped with slotted head grease screws, remove the
screw and insert a two-inch to three-inch long grease string into each
hole on motors in NEMA 215 frame and smaller.
Insert a three-inch to five-inch length on larger motors. For motors
having grease drain plugs, remove the plug and operate the motor for
20 minutes before replacing the plugs.
Relubrication Intervals Chart
For Motors Having Grease Fittings
Hours of Service HP Range Suggested
Per YearRelube Interval
50001/18 to 7 1/2
5 years
10 to 403 years
50 to 1001 year
Continuous Normal
to 7 1/22 years
Applications10 to 401 year
50 to 1009 months
Seasonal Service -
1 year
Motor is idle for(beginning of
6 months or moreseason)
Continuous high
ambient, high
vibrations, or where
shaft end is hot
1/8 to 40
50 to 150
6 months
3 months
Caution: Keep grease clean. Lubricate motors at a standstill. Do not mix petroleum
grease and silicone grease in motor bearings.
Motor takes too long to accelerate.
Verify brush length.
Inspect bearings for proper service. Noisy or rough bearings should be replaced.
Brushes are worn.
Bearings may be defective.
Verify that the brushes are properly seated and measure their length against the
recommended brush length chart.
Brushes may not be seated properly or
worn beyond their useful length.
The accel trim pot of the controller should be adjusted.
Inspect the armature for an open connection.
Motor may have an open connection.
Motor controller not properly set.
Check controller manual for adjustments. The torque and/or IR compensation
settings may need adjustment.
Motor controller not properly set.
Verify voltage is coming out of the controller.
Controller may be defective.
Verify the load has not changed. Measure the amp draw of motor against the full
load amp rating of the motor. If the amp draw is higher than rating, motor is
undersized for application.
Inspect the brushes to make sure that they are still making contact with the
commutator. Refer to manufacturer’s recommended brush length chart.
The brushes may be worn down too far and no
longer make contact with the commutator.
Load has increased.
Disassemble motor and inspect the armature for a burnt coil. Inspect the
commutator for burnt bars. If this condition exists, the motor needs to be replaced.
To test, set your OHM to the RX1 scale, touch probes to bars 180 degrees apart all
around the commutator. The reading should be equal.
Armature is shorted or went to ground.
Motor may make a humming noise and
the circuit breaker or fuse will trip.
Motor runs but loses power.
Replace the fuse or reset the breaker
What To Do
Likely Causes
Fuse or circuit breaker is tripped
Motor has been running,
then fails to start.
DC Motor Trouble-Shooting Chart
May be able to reassemble; otherwise, motor should be replaced.
Replace fuse or reset breaker.
Disassemble motor and inspect windings and internal connections. A
blown stator will show a burn mark. Motor must be replaced or the stator
Motor damaged and rotor is striking stator.
Fan guard bent and contacting fan.
Fuse or circuit breaker tripped.
Stator is shorted or went to ground. Motor will make
a humming noise and the circuit breaker or fuse will trip.
Motor had been running, then fails
to start.
Inspect to see that the load is free. Verify amp draw of motor versus
nameplate rating.
First discharge capacitor. To check capacitor, set volt-ohm meter to RX100 scale and touch its probes to capacitor terminals. If capacitor is OK, needle will jump to zero ohms, and drift back to high. Steady zero ohms indicates a short circuit; steady high ohms indicates an open circuit.
Motor overloaded or load jammed.
Capacitor (on shingle phase motor) may have failed.
Replace fan guard.
Verify that the motor is wired correctly.
Motor is miswired.
What To Do
Motor fails to start upon
initial installation.
Likely Causes
Disconnect power to the motor before performing service or maintenance.
Discharge all capacitors before servicing motor.
Always keep hands and clothing away from moving parts.
Be sure required safety guards are in place before starting equipment.
AC Motor Trouble-Shooting Chart
Noisy or rough feeling bearings should be replaced.
Motor overload protector Load too high.
continually trips.
Verify that the load is not jammed. If motor is a replacement, verify that the rating is the same as the old motor. If previous motor was a special design, a stock motor may not be able to duplicate the performance. Remove the load from the motor and inspect the amp draw of the motor unloaded. It should be less than the full load rating stamped on the nameplate.
Rewire motor according to wiring schematic provided.
Motor runs in the wrong rotation.
Incorrect wiring.
Make sure that the voltage is within 10% of the motor’s nameplate
rating. If not, contact power company or check if some other equipment is taking power away from the motor.
Voltage too low.
Bad bearings.
Inspect switch contacts and connections. Verify that switch reeds have some spring in them.
Test capacitor per previous instructions.
Faulty stationary switch.
Defective capacitor.
Verify the load has not changed. Verify equipment hasn’t got tighter. If fan application verify the air flow hasn’t changed.
Load increased.
Motor takes too long to accelerate.
If voltage is less than 10% of the motor’s rating contact power company or check if some other equipment is taking power away from the motor.
Motor runs but dies down.
Voltage drop.
What To Do
Disassemble motor and inspect both the centrifugal and stationary switches. The weights of the centrifugal switch should move in and out freely. Make sure that the switch is not loose on the shaft. Inspect
contacts and connections on the stationary switch. Replace switch if the contacts are burned or pitted.
Likely Causes
Motor had been running, then fails
Starting switch has failed.
to start. (cont’d)
AC Motor Trouble-Shooting Chart
Realign load.
Remove motor from load and inspect motor by itself. Verify that motor shaft is not bent. Rule of thumb is .001” runout per every inch of shaft length.
Test motor by itself. If bearings are bad,you will hear noise or feel
roughness. Replace bearings. Add oil if the bearing is a sleeve bearing type or replace bearings. Add grease if bearings have grease fittings.
Inspect motor by itself with no load attached. If it feels rough and vibrates but the bearings are good, it may be that the rotor was
improperly balanced at the factory. Rotor must be replaced or
With the motor disconnected from power turned shaft. It should move but with some resistance. If the shaft moves in and out too freely, this may indicate a preload problem and te bearings may need additional shimming.
Test winding for shorted or open circuits. The amps may also be high. Replace motor or have stator rewound.
Winding shorted or grounded.
Motor vibrates.
Motor misaligned to load.
Load out of balance.
(Direct drive application).
Motor bearings defective.
Rotor out of balance.
Motor may have too much endplay.
Winding may be defective.
Inspect stator for defects, or loose or cut wires that may cause it to go toground.
Replace the motor’s protector with a new one of the same rating.
Protector may be defective.
What To Do
Verify that the motor is getting enough air for proper cooling. Most motors are designed to run in an ambient temperature of less than 40° C. (Note: A properly operating motor may be hot to the touch.)
Likely Causes
Motor overload protector Ambient temperature too high.
continually trips. (cont’d)
AC Motor Trouble-Shooting Chart
Ensure that motor was not damaged in shipment. Frame damage may not be repairable. If you cannot see physical damage, inspect the motor’s rotor and stator for strike marks. If signs of rubbing are present, the motor should be replaced. Sometimes simply disassembling and reassembling motor eliminates rubbing. Endbells are also sometimes knocked out of alignment during transportation.
Motor may not be sized properly. Verify how long the motor takes to come up to speed. Most single phase capacitor start motors should come up to speed within three seconds. Otherwise the capacitors may fail.
Verify duty cycle. Capacitor manufactures recommend no more than 20,
three-second starts per hour. Install capacitor with higher voltage rating, or add bleed resistor to the capacitor.
Verify that voltage to the motor is within 10% of the nameplate value. If the motor is rated 208-230V, the deviation must be calculated from 230V.
Replace switch.
The motor, at start up, makes a loud Rotor may be striking stator.
rubbing or grinding noise.
Start capacitors continuously fail.
The motor is not coming up to speed quickly enough.
The motor is being cycled too frequently.
Voltage to motor is too low.
Starting switch may be defective, preventing the motor
from coming out of start winding.
Ambient temperature too high.
Possible power surge to motor, caused by lightning
strike or other high transient voltage.
Run capacitor fail.
If a common problem, install surge protector.
Verify that ambient does not exceed motor’s nameplate value.
If the motor is used in a high ambient, a different type of bearing grease may be required. You may need to consult the factory or a bearing
High ambient temperature.
What To Do
Besides checking load, also inspect drive belt tension to ensure it’s not too tight may be too high. An unbalanced load will also cause the Bearings to fail.
Likely Causes
Bearings continuously fail.
Load to motor may be excessive or unbalanced.
AC Motor Trouble-Shooting Chart
Common Motor Types and
Typical Applications
Alternating Current Designs
Single Phase * Rigid Base Mounted * Capacitor Start * Totally Enclosed Fan
Cooled (TEFC) & Totally Enclosed Non-Vent (TENV)
General purpose including compressors, pumps, fans, farm equipment,
conveyors, material handling equipment and machine tools.
Single Phase * Rigid Base Mounted * Capacitor Start * Open Drip
Proof (ODP)
General purpose including compressors, pumps, conveyors, fans,
machine tools and air conditioning units - usually inside or where protected from weather, dust and contaminants.
Three Phase * Rigid Base Mounted * TEFC
General purpose including pumps, compressors, fans, conveyors,
machine tools and other applications where three-phase power is
Three Phase * Rigid Base Mounted * ODP
General purpose including pumps, compressors, machine tools, conveyors, blowers, fans and other applications requiring three-phase power,
usually inside or where protected from weather, dust and contaminants.
Single Phase * NEMA C Face Less Base * Capacitor Start * TEFC &
Pumps, fans, conveyors, machine tools and gear reducers.
Single Phase * NEMA C Face Less Base * Capacitor Start * ODP
Fans, blowers, compressors, tools and speed reducers.
Three Phase * NEMA C Face Less Base * TEFC & TENV
Fans, blowers, compressors, tools and speed reducers where threephase power is suitable.
Three Phase * NEMA C Face Less Base * ODP
Fans, blowers, compressors, tools and speed reducers.
Wash-Thru and Multiguard Motors
Used in applications involving moisture, vibration, dust and some
chemical contact. The motor’s windings are impregnated and encapsulated in a thermosetting that protects them from contaminants for long
motor life.
Automotive Duty Motors
Suited for a wide variety of tough applications found in automotive
manufacturing facilities and other industries utilizing U-Frame motors.
Meets or exceeds General Motors GM-7EH and –7EQ, Ford EM1 and
Chrysler NPEM-100 specifications.
Crusher Duty Motors
Ideally suited for size reduction equipment including rock crushers and
pulverizers and other uses the aggregate and construction industries.
They are designed for belted (radial) loads only utilizing roller bearings
on the Drive-end side of the motor.
Washdown-Duty * Single & Three Phase * TENV & TEFC
Extended life in applications requiring regular hose-downs with
cleaning solutions, as in food processing and for applications in wet,
high humidity environments. Also available in direct current designs.
Explosion Proof * Single & Three Phase * TENV & TEFC
Designed and listed for application in hazardous environments having
certain explosive gases or materials present on equipment, such as
blowers, pumps, agitators or mixers.
Chemical Service Motors * Rigid Base
Petrochemical plants, foundries, pulp and paper plants, waste management facilities, chemical plants, tropical climates and other processing
industry applications requiring protection against corrosion caused by
severe environmental operating conditions.
Brakemotors * Single & Three Phase
Machine tools, hoists, conveyors, door operators, speed reducers,
valves, etc., when stop and hold performance is required when power is
removed from the motor by the use of a spring-set friction brake.
Resilient Mounted * Single & Three Phase * Moderate Starting
General purpose applications where quiet operation is preferred for fan
and blower service.
Resilient Mounted * Single & Three Phase * Two Speed * Two
Winding * Variable Torque:
Belted or fan-on-shaft applications.
Rigid Mounted * Totally Enclosed Air Over (TEAO) * Single & Three
Dust-tight motors for shaft-mounted or belt-driven fans. The motor
depends upon the fan’s airflow to cool itself.
HVAC Blower Motors * Three Phase * Automatic Reset Overload
Protector * Resilient Base * ODP
Heating, ventilating and air conditioning applications requiring moderate starting torque and thermal protection.
Condenser Fan Motors * Three Phase * Belly Band Mount * ODP
For operating vertical shaft-up on condenser fan, air-over applications,
such as rooftop air conditioning units.
Two Speed * Three Phase * Variable Torque
Fans, blowers and centrifugal pumps. Variable torque motors have
horsepower ratings that vary as the square of the speed, while torque
varies directly with the speed.
Two Speed * Three Phase * Constant Torque
Mixers, compressors, conveyors, printing presses, extractors, feeders
and laundry machines. Constant torque motors are capable of developing the same torque for all speeds. Their horsepower ratings vary
directly with the speed.
Two Speed * Three Phase * Constant Horsepower
Machine tools, such as drills, lathes, punch presses and milling
machines. Constant horsepower motors develop the same horsepower
at all operating speeds, and the torque varies inversely with the speed.
Jet Pump Motors * Single & Three Phase
Residential and industrial pumps, plus swimming pool pumps. The pump
impeller is mounted to the motor shaft.
JM Pump Motors * Single & Three Phase
Continuous duty service on close-coupled pumps using NEMA JM
mounting provisions. Commonly used for circulating and transferring
fluids in commercial and industrial water pumps.
Compressor Duty * Single & Three Phase
Air compressor, pump-fan and blower duty applications which require
high breakdown torque and overload capacity matching air compressor
loading characteristics.
Woodworking Motors * Single Phase * TEFC
High torques for saws, planers and similar woodworking equipment.
Instant Reversing Motors * Resilient Mount * Single Phase * ODP
Specially designed motors for use on instant-reversing parking gates,
doors, slide gates or other moderate starting torque instant reversing
application; capable of frequent reversing service.
Pressure Washer Pump Motors * Rigid Mount & Rigid Mount with
NEMA C Face * Single Phase * ODP
Hot or cold pressure washers and steam cleaners.
IEC Metric Motors * Three Phase
For replacement on imported machined tools, textile machinery and
other equipment having metric dimensioned motors. Also available in
direct current designs.
Farm Duty * High Torque & Extra High Torque * Rigid Base Mount &
C Face Less Base
Severe agricultural equipment applications requiring high torques under
adverse operating conditions such as low temperatures.
Agricultural Fan Duty * Resilient & Rigid Base Mount * Single & Three
Phase * TEAO
Dust-tight fan and blower duty motors for shaft-mounted or belt-driven
fans. The motor depends upon the fan’s air flow to cool itself.
Feed-Auger Drive Motors * Single Phase
Dust-tight auger motors eliminate damage caused when the motor is
over-speeded by an obstructed auger. Special flange mounts directly
to the auger gear reducer.
Hatchery/Incubator Fan Motor * Band Mounted * Single Phase *
Replacement for use on poultry incubator fans. Includes extended
through bolts for attaching farm shroud.
Feather Picker Motor * Rigid Mount * Three Phase * TEFC
Washdown-duty motor replaces the MEYN drive motor of a processing
machine that removes feathers from poultry.
Milk Transfer Pump Motor * Rigid Base * Single Phase * TENV
Replacement in dairy milk pumps.
Grain Stirring Motors * Rigid Base * Single Phase * TEFC
Designed to operate inside agricultural storage bins for stirring grain,
corn, and other agricultural products during the drying and storage
Irrigation Drive Motors * C Face Less Base * Three Phase * TEFC
For center pivot irrigation systems exposed to severe weather environments and operating conditions. Drives the tower that propels sprinklers
in a circle around the well.
Severe Duty and IEEE 841 Motors
Designed to meet severe duty environments that you might find in chemical
plants, foundries, Paper and Pulp mills or waste management facilities.
IEEE-841 motors meet IP56 enclosure protection and approved for
USCG Marine Duty, AP1, RP14F for offshore platforms.
Elevator Motors
Submersible Hydraulic Elevator Pump Motors
Used in Elevator systems for applications in hydraulic passenger, service,
freight and low-rise elevators.
Hydraulic Elevator Pump Motors
Used in Hydraulic pump passenger, service, freight and dumbwaiter low
rise elevators
VVVF (Variable Voltage Variable Frequency) Traction Elevator Hoist
Designed for Geared and Gearless Traction Elevators.
Direct Current Designs
High-Voltage, SCR-Rated Brush-Type * Permanent Magnet Field * C
Face With Removable Base * TEFC
Generally used for conveyors, machine tools, hoists or other applications requiring smooth, accurate adjustable-speed capabilities through
the use of thyristor-based controls, often with dynamic braking and
reversing also required. Usually direct-coupled to driven machinery, with
the motor often additionally supported by a base for maximum rigidity.
Such motors are also applicable where extremely high starting torque,
or high intermittent-duty running torques are needed, even if the application may not require adjustable speed.
High-Voltage, SCR-Rated Brush-Type * Permanent Magnet Field *
Washdown-Duty Enhancements * C Face With Removable Base *
Designed for extended life on food-processing machines or other highhumidity environments where adjustable speed is required.
Low-Voltage Brush-Type * Permanent Magnet Field * C Face With
Removable Base * TENV
For installations operating from battery or solar power, or generatorsupplied low-voltage DC. One key application is a pump operating off a
truck battery. Like high-voltage counterparts, low-voltage designs provide linear speed/torque characteristics over their entire speed range, as
well as dynamic braking, easy reversing and high torque.
Gear Reducers and Gearmotors
A gear reducer, also called a speed reducer or gear box, consists of
a set of gears, shafts and bearings that are factory-mounted in an
enclosed, lubricated housing. Gear reducers are available in a broad
range of sizes, capacities and speed ratios. Their job is to convert the
input provided by a “prime mover” into output of lower RPM and correspondingly higher torque. In industry, the prime mover is most often an
electric motor, though internal combustion engines or hydraulic motors
may also be used.
Cutaway view shows key components of an industrial-duty worm
gear reducer. Note steel worm and
bronze worm gear. Seals on both
input and output shafts prevent
lubricant leakage.
There are many types of gear reducers using various gear types to meet
application requirements as diverse as low first cost, extended life,
limited envelope size, quietness, maximum operating efficiency, and a
host of other factors. The discussion that follows is intended only as a
brief outline of the most common industrial gear reducer types, their
characteristics and uses.
Right-Angle Worm Gear Reducers
The most widely used industrial gear reducer type is the right-angle
worm reducer. Worm reducers offer long life, overload and shock load
tolerance, wide application flexibility, simplicity and relatively low cost.
In a worm gear set, a threaded input shaft, called the worm, meshes with
a worm gear that is mounted to the output shaft. Usually, the worm
shaft is steel and the worm gear is bronze. This material combination
has been shown to result in long life, smooth operation, and noise levels
acceptable for industrial environments.
The number of threads in the worm shaft, related to the number of teeth
in the worm gear, determine the speed reduction ratio. Single-reduction
worm gear reducers are commonly available in ratios from approximately
5:1 through 60:1. A 5:1 ratio means that motor input of 1750 RPM is converted to 350 RPM output. A 60:1 ratio brings output RPM of the same
motor to 29 RPM. Greater speed reductions can be achieved through
double-reduction – meaning two gear reducers coupled together.
The flip side of “geared-down” speed is “geared-up” torque. For the
majority of gear reducers in North America, output torque is expressed
in inch-pounds or foot-pounds. Outside of North America, the metric
unit of torque, newton-meter, is most common. Output speed and
output torque are the key application criteria for a gear reducer.
Parallel-Shaft Gear Reducers
Parallel-shaft units are typically built with a combination of helical and
spur gears in smaller sizes, and all helical gears in larger sizes. Helical
gears, which have teeth cut in helixes to maximize gear-to-gear contact,
offer higher efficiencies and quieter operation – though at a correspondingly higher cost than straight-tooth spur gears.
Single-reduction speed ratios are far more limited in parallel-shaft
reducers than in right-angle worm reducers, but multiple reductions (or
gear stages) fit easily within a single parallel-shaft reducer housing. As
a result, the availability of higher ratios is usually greater in parallel-shaft
reducers and gearmotors; ratios as high as 900:1 are common in small
Combination of spur and helical
gears can be seen in this cutaway
view of a sub-fractional horsepower
parallel-shaft gearbox. Note multiple
gear stages.
Three-phase NEMA C face AC
motor combined with flanged
worm gear reducer results in a
“workhorse” industrial gearmotor. This straightforward
mounting approach is common
with motors ranging in sizes
from fractional through 20 HP
and larger.
An electric motor combined with a gear reducer creates a gearmotor.
In sub-fractional horsepower sizes, integral gearmotors are the rule –
meaning the motor and the reducer share a common shaft and cannot
be separated. For application flexibility and maintenance reasons, a
larger gearmotor is usually made up of an individual reducer and motor
coupled together. This is most often accomplished by using a reducer
having a NEMA C input flange mated to a NEMA C face motor.
At left, a quill-style input worm gear reducer uses a hollow input shaft and a
shallow mounting flange. At right, extended mounting flange accommodates a
solid-shaft to solid-shaft input with a flexible coupling joining the two shafts.
NEMA C flange reducers are of two basic types based on how the
motor and reducer shafts are coupled. The most straightforward type,
and the most commonly used in smaller horsepower applications, has a
“quill” input – a hollow bore in the worm into which the motor’s shaft is
inserted. The other type, involving a reducer having a solid input shaft,
requires a shaft-to-shaft flexible coupling, as well as an extended NEMA
C flange to accommodate the combined length of the shafts.
Installation and Application Considerations
Mounting: In the majority of cases, gear reducers are base-mounted.
Sometimes, mounting bolts are driven directly into pre-threaded holes
in the reducer housing. Other times, accessory bases are used. Output
flange mountings are also available.
Quill-style input reducer with
added base; “worm over”
mounting position
Shaft-input reducer in vertical
position, deep NEMA C flange,
plus “J style” base
Vertical output shaft, extendedheight base, solid input shaft with
no mounting flange
Quill-input reducer with output
flange added
Basic worm gear reducers can be easily modified with mounting accessories to
meet application needs. Four examples are shown.
Reducers having hollow output shafts are usually shaft-mounted to the
driven load. If no output flange or secondary base is used, a reaction
arm prevents the reducer housing from rotating.
Hollow output shaft reducer with
reaction arm mounted. This model
also has quill input and shallow
NEMA C input flange.
Do not mount reducers with the input shaft facing down. Other than
that, they may generally be mounted in any orientation. If the reducer is
vented, be sure the vent plug is moved to a location as close as possible
to the top of the unit, as shown in the examples below.
Output Speed and Torque: These are the key criteria for matching a
gear reducer to the application needs.
Center Distance: The basic measurement or size reference for worm
gear reducers. Generally, the larger the center distance, the greater the
reducer capacity. Center distance is measured from the centerline of
the input shaft to the centerline of the output shaft.
Horsepower: A reducer’s input horsepower rating represents the
maximum prime mover size the reducer is designed to handle. Output
horsepower, while usually listed by reducer manufacturers, has little
application relevance. Speed and torque are the real considerations.
Overhung Load: This is a force applied at right angles to a shaft beyond
the shaft’s outermost bearing. Too much overhung load can cause
bearing or shaft failure. Unless otherwise stated, a reducer manufacturer’s overhung load maximums are rated with no shaft attachments such as sheaves or sprockets. The American Gear Manufacturers
Association provides factors, commonly called “K” factors, for various
shaft attachments by which the manufacturer’s maximum should be
reduced. Overhung load can be eased by locating a sheave or sprocket
as close to the reducer bearing as possible. In cases of extreme overhung load, an additional outboard bearing may be required.
The following formula can be used to calculate overhung load (OHL):
OHL (pounds) =
Torque (inch-pounds) x K (load factor constant of overhung load)
R (radius of pulley, sprocket or gear)
where, K equals 1.00 for chain and sprocket, 1.25 for a gear, and 1.5 for
a pulley and v-belt.
Thrust Load: This is a force applied parallel to a shaft’s axis. Mixers,
fans and blowers are among driven machines that can induce thrust
loads. Exceeding manufacturers’ maximums for thrust loading can
cause premature shaft and bearing failure.
Mechanical and Thermal Ratings: Mechanical ratings refer to the maximum power a reducer can transmit based on the strength of its components.
Many industrial reducers, including Marathon Motors, provide a 200%
safety margin over this rating for start-ups and momentary overloads.
Thermal rating refers to the power a reducer can transmit continuously
based on its ability to dissipate the heat caused by operating friction.
In practice, the mass of a cast iron reducer housing and its oil lubrication
system provide sufficient heat dissipation so that mechanical and thermal
ratings are essentially equal. Aluminum-housed or grease-lubricated
reducers have less heat dissipation mass and therefore require consideration of thermal rating.
Graphic shows compact size
of an aluminum-housed worm
gear reducer compared with a
cast iron housed reducer of the
same center distance. Smaller
size and lighter weight can be
an application advantage in
many cases, but reduced mass
means that the reducer’s
thermal rating must be
carefully considered.
Service Factor: Established by the American Gear Manufacturers
Association (AGMA), gearing service factors are a means to adjust a
reducer’s ratings relative to an application’s load characteristics. Proper
determination of an application’s service factor is critical to maximum
reducer life and trouble-free service. Unless otherwise designated,
assume a manufacturer’s ratings are based on an AGMA-defined service
factor of 1.0, meaning continuous operation for 10 hours per day or less
with no recurring shock loads. If conditions differ from this, input horsepower and torque ratings must be multiplied by the service factor selected
from one of the tables below. In addition, AGMA has standardized service factor data for a wide variety of specific applications. Contact your
manufacturer for this information.
Input Speed: Gear reducers are best driven at input speeds common
in industrial electric motors, typically 1200, 1800 or 2500 RPM. This
provides sufficient “splash” for the reducer’s lubrication system, but not
so much as to cause oil “churning.” For input speeds under 900 RPM
or above 3000 RPM, consult the manufacturer. Alternative lubricants
may be suggested.
Service Factor Conversions for Reducers
With Electric or Hydraulic Motor Input
Duration of Service
(Hours per day)
Occasional 1/2 Hour
Less than 3 Hours
3 - 10 Hours
Over 10 Hours
* Unspecified service factors should be 1.00 or as agreed upon by the user and manufacturer.
Service Factor Conversions for Reducers
With Engine Input
Hydraulic or Electric
Single Cylinder
Special Environmental Considerations
Gear reducers are extremely rugged pieces of equipment with long life
in most types of power transmission applications. Modern components,
including seals and synthetic lubricants, are designed for sustained hightemperature operation. Extreme heat, however, can be a problem. As
a rule of thumb, maximum oil sump temperature for a speed reducer
is 200ºF, or 100ºF above ambient temperature, whichever is lower.
Exceeding these guidelines can shorten the reducer’s life. Be sure to
provide adequate air space around a reducer for heat dissipation. In
some cases, it may be necessary to provide an external cooling fan. In a
gearmotor application, the fan on a totally enclosed, fan cooled motor
can also aid in cooling the reducer.
Moisture or high humidity is another concern. A key instance of this
is a food processing environment requiring washdowns. In such cases,
consider reducers with special epoxy coatings, external shaft seals, and
stainless steel shaft extensions and hardware. If a gearmotor is used, be
sure the motor has similar washdown-duty features.
Gear Reducer Maintenance
Industrial gear reducers require very little maintenance, especially if
they have been factory-filled with quality, synthetic lubricant to a level
sufficient for all mounting positions. In most cases, oil change will not
be necessary over the life of the reducer. It is recommended that oil be
changed only if repair or maintenance needs otherwise dictate gearbox
Oil level should, however, be checked periodically and vent plugs
inspected to ensure they are clean and operating.
Otherwise, general maintenance procedures for any industrial equipment
apply. This includes making sure mounting bolts and other attachments
are secure and that no other unusual conditions have occurred.
Adjustable Speed Drives
By definition, adjustable speed drives of any type provide a means of
variably changing speed to better match operating requirements. Such
drives are available in mechanical, fluid and electrical types.
The most common mechanical versions use combinations of belts and
sheaves, or chains and sprockets, to adjust speed in set, selectable
ratios – 2:1, 4:1, 8:1 and so forth. Traction drives, a more sophisticated mechanical control scheme, allow incremental speed adjustments.
Here, output speed is varied by changing the contact points between
metallic disks, or between balls and cones.
Adjustable speed fluid drives provide smooth, stepless adjustable speed
control. There are three major types. Hydrostatic drives use electric
motors or internal combustion engines as prime movers in combination
with hydraulic pumps, which in turn drive hydraulic motors. Hydrokinetic
and hydroviscous drives directly couple input and output shafts.
Hydrokintetic versions adjust speed by varying the amount of fluid in a
vortex that serves as the input-to-output coupler. Hydroviscous drives,
also called oil shear drives, adjust speed by controlling oil-film thickness,
and therefore slippage, between rotating metallic disks.
An eddy current drive, while technically an electrical drive, nevertheless
functions much like a hydrokinetic or hydroviscous fluid drive in that
it serves as a coupler between a prime mover and driven load. In an
eddy current drive, the coupling consists of a primary magnetic field
and secondary fields created by induced eddy currents. The amount of
magnetic slippage allowed among the fields controls the driving speed.
In most industrial applications, mechanical, fluid or eddy current drives
are paired with constant-speed electric motors. On the other hand,
solid state electrical drives (also termed electronic drives), create adjustable speed motors, allowing speeds from zero RPM to beyond the
motor’s base speed. Controlling the speed of the motor has several
benefits, including increased energy efficiency by eliminating energy
losses in mechanical speed changing devices. In addition, by reducing,
or often eliminating, the need for wear-prone mechanical components,
electrical drives foster increased overall system reliability, as well as
lower maintenance costs. For these and other reasons, electrical drives
are the fastest growing type of adjustable speed drive.
There are two basic drive types related to the type of motor controlled –
DC and AC. A DC direct current drive controls the speed of a DC motor
by varying the armature voltage (and sometimes also the field voltage).
An alternating current drive controls the speed of an AC motor by
varying the frequency and voltage supplied to the motor.
DC Drives
Direct current drives are easy to apply and technologically straightforward.
They work by rectifying AC voltage from the power line to DC voltage,
then feeding adjustable voltage to a DC motor. With permanent magnet
DC motors, only the armature voltage is controlled. The more voltage
supplied, the faster the armature turns. With wound-field motors, voltage must be supplied to both the armature and the field. In industry, the
following three types of DC drives are most common:
A general-purpose DC SCR
drives family. From left,
NEMA 4/12 “totally enclosed”
version, chassis-mount,
NEMA 1 “open” enclosure.
DC SCR Drives: These are named for the silicon controlled rectifiers
(also called thyristors) used to convert AC to controlled voltage DC.
Inexpensive and easy to use, these drives come in a variety of enclosures, and in unidirectional or reversing styles.
Regenerative SCR Drives: Also called four quadrant drives, these allow
the DC motor to provide both motoring and braking torque. Power
coming back from the motor during braking is regenerated back to the
power line and not lost.
Pulse Width Modulated DC Drives: Abbreviated PWM and also called,
generically, transistorized DC drives, these provide smoother speed
control with higher efficiency and less motor heating. Unlike SCR drives,
PWM types have three elements. The first converts AC to DC, the second filters and regulates the fixed DC voltage, and the third controls
average voltage by creating a stream of variable width DC pulses. The
filtering section and higher level of control modulation account for the
PWM drive’s improved performance compared with a common SCR
AC Drives
AC drive operation begins in much the same fashion as a DC drive.
Alternating line voltage is first rectified to produce DC. But because an
AC motor is used, this DC voltage must be changed back, or inverted,
to an adjustable-frequency alternating voltage. The drive’s inverter section accomplishes this. In years past, this was accomplished using SCRs.
However, modern AC drives use a series of transistors to invert DC to
adjustable-frequency AC.
With advances in power electronics,
even so-called “micro” drives can be
used with motors 40 HP or higher.
Full-featured unit shown includes
keypad programming and alphanumeric display.
This synthesized alternating current is then fed to the AC motor at the
frequency and voltage required to produce the desired motor speed.
For example, a 60 hz synthesized frequency, the same as standard line
frequency in the United States, produces 100% of rated motor speed.
A lower frequency produces a lower speed, and a higher frequency a
higher speed. In this way, an AC drive can produce motor speeds from,
approximately, 15 to 200% of a motor’s normally rated RPM – by
delivering frequencies of 9 hz to 120 hz, respectively.
Today, AC drives are becoming the systems of choice in many industries.
Their use of simple and rugged three-phase induction motors means that
AC drive systems are the most reliable and least maintenance prone of all.
Plus, microprocessor advancements have enabled the creation of so-called
vector drives, which provide greatly enhance response, operation down
to zero speed and positioning accuracy. Vector drives, especially when
combined with feedback devices such as tachometers, encoders and
resolvers in a closed-loop system, are continuing to replace DC drives in
demanding applications.
“Sub-micro” drives provide a
wide array of features in a very
small package.
By far the most popular AC drive today is the pulse width modulated
type. Though originally developed for smaller-horsepower applications,
PWM is now used in drives of hundreds or even thousands of horsepower
– as well as remaining the staple technology in the vast majority of small
integral and fractional horsepower “micro” and “sub-micro” AC drives.
Pulse width modulated refers to the inverter’s ability to vary the output
voltage to the motor by altering the width and polarity of voltage pulses.
The voltage and frequency are sythesized using this stream of voltage
pulses. This is accomplished through microprocessor commands to a
series of power semiconductors that serve as on-off switches. Today,
these switches are usually IGBTs, or isolated gate bipolar transistors. A
big advantage to these devices is their fast switching speed resulting in
higher pulse or carrier frequency, which minimizes motor noise.
“One Piece” Motor/Drive Combinations
Variously called intelligent motors, smart motors or integrated motors
and drives, these units combine a three-phase electric motor and a
pulse width modulated inverter drive in a single package. Some designs
mount the drive components in what looks like an oversize conduit box.
Other designs integrate the drive into a special housing made to blend
with the motor. A supplementary cooling fan is also frequently used
for the drive electronics to counteract the rise in ambient temperature caused by being in close proximity to an operating motor. Some
designs also encapsulate the inverter boards to guard against damage
from vibration.
Size constraints limit integrated drive and motor packages to the smaller
horsepower ranges and require programming by remote keypad, either
hand-held or panel mounted. Major advantages are compactness and
elimination of additional wiring.
One-piece motor and drive
combinations can be a pre-packaged solution in some applications. Unit shown incorporates
drive electronics and cooling
system in a special housing at
the end of the motor.
AC Drive Application Factors
As PWM AC drives have continued to increase in popularity, drives manufacturers have spent considerable research and development effort to
build in programmable acceleration and deceleration ramps, a variety of
speed presets, diagnostic abilities, and other software features. Operator
interfaces have also been improved with some drives incorporating “plainEnglish” readouts to aid set-up and operation. Plus, an array of input
and output connections, plug-in programming modules, and off-line programming tools allow multiple drive set-ups to be installed and maintained in a fraction of the time spent previously. All these features have
simplified drive applications. However, several basic points must be
Torque: This is the most critical application factor. All torque requirements must be assessed, including starting, running, accelerating and
decelerating and, if required, holding torque. These values will help
determine what current capacity the drive must have in order for the
motor to provide the torque required. Usually, the main constraint is
starting torque, which relates to the drive’s current overload capacity.
(Many drives also provide a starting torque boost by increasing voltage
at lower frequencies.)
Perhaps the overriding question, however, is whether the application
is variable torque or constant torque. Most variable torque applications fall into one of two categories – air moving or liquid moving – and
involve centrifugal pumps and fans. The torque required in these
applications decreases as the motor RPM decreases. Therefore, drives
for variable torque loads require little overload capacity. Constant
torque applications, including conveyors, positive displacement pumps,
extruders, mixers or other “machinery” require the same torque regardless of operating speed, plus extra torque to get started. Here,
high overload capacity is required.
Smaller-horsepower drives are often built to handle either application.
Typically, only a programming change is required to optimize efficiency
(variable volts-to-hertz ratio for variable torque loads, constant volts-tohertz ratio for constant torque loads). Larger horsepower drives are usually built specifically for either variable or constant torque applications.
Speed: As mentioned, AC drives provide an extremely wide speed
range. In addition, they can provide multiple means to control
this speed. Many drives, for example, include a wide selection of
preset speeds, which can make set-up easier. Similarly, a range of
acceleration and deceleration speed “ramps” are provided. Slip
compensation, which maintains constant speed with a changing
load, is another feature that can be helpful. In addition, many
drives have programmable “skip frequencies.” Particularly with fans
or pumps, there may be specific speeds at which vibration takes
place. By programming the drive to avoid these corresponding frequencies, the vibration can be minimized. Another control function,
common with fans, is the ability for the drive to start into a load already
in motion – often called a rolling start or spinning start. If required, be
sure your drive allows this or you will face overcurrent tripping.
Current: The current a motor requires to provide needed torque (see
previous discussion of torque) is the basis for sizing a drive. Horsepower
ratings, while listed by drives manufacturers as a guide to the maximum
motor size under most applications, are less precise. Especially for
demanding constant torque applications, the appropriate drive may, in
fact, be “oversized” relative to the motor. As a rule, general-purpose
constant torque drives have an overload current capacity of approximately 150% for one minute, based on nominal output. If an application
exceeds these limits, a larger drive should be specified.
Power Supply: Drives tolerate line-voltage fluctuations of 10-15% before
tripping and are sensitive to power interruptions. Some drives have
“ride-through” capacity of only a second or two before a fault is triggered, shutting down the drive. Drives are sometimes programmed for
multiple automatic restart attempts. For safety, plant personnel must
be aware of this. Manual restart may be preferred.
Most drives require three-phase input. Smaller drives may be available
for single-phase input. In either case, the motor itself must be threephase.
Drives, like any power conversion device, create certain power
disturbances (called “noise” or “harmonic distortion”) that are reflected
back into the power system to which they are connected. These
disturbances rarely affect the drive itself but can affect other electrically
sensitive components.
Control Complexity: Even small, low-cost AC drives are now being
produced with impressive features, including an array of programmable
functions and extensive input and output capability for integration
with other components and control systems. Additional features may
be offered as options. Vector drives, as indicated previously, are one
example of enhanced control capability for specialized applications.
In addition, nearly all drives provide some measure of fault logging and
diagnostic capability. Some are extensive, and the easiest to use display the information in words and phrases rather than simply numerical
Environmental Factors: The enemies of electronic components are
well-known. Heat, moisture, vibration and dirt are chief among them
and obviously should be mitigated. Drives are rated for operation in
specific maximum and minimum ambient temperatures. If the maximum
ambient is exceeded, extra cooling must be provided, or the drive may
have to be oversized. High altitudes, where thinner air limits cooling
effectiveness, call for special consideration. Ambient temperatures too
low can allow condensation. In these cases, or where humidity is generally high, a space heater may be needed.
Drive enclosures should be selected based on environment. NEMA 1
enclosures are ventilated and must be given room to “breath.” NEMA
4/12 enclosures, having no ventilation slots, are intended to keep dirt
out and are also used in washdown areas. Larger heat sinks provide
convection cooling and must not be obstructed, nor allowed to become
covered with dirt or dust. Higher-horsepower drives are typically supplied within NEMA-rated enclosures. “Sub-micro” drives, in particular,
often require a customer-supplied enclosure in order to meet NEMA
and National Electrical Code standards. The enclosures of some “micro”
drives, especially those cased in plastic, may also not be NEMA-rated.
Speed Setpoint
Drive Status
RUN > 56.00 HZ
Speed Units
Direction (Forward)
Percent Load
Drive Status
R UN > 85%
Direction (Forward)
Speed Setpoint
Drive Status
Examples of operating and diagnostic displays in a modern AC drive.
Motor Considerations With AC Drives
One drawback to pulse width modulated drives is their tendency to produce voltage spikes, which in some instances can damage the insulation
systems used in electric motors. This tendency is increased in applications
with long cable distances (more than 50 feet) between the motor and drive
and with higher-voltage drives. In the worst cases, the spikes can literally
“poke a hole” into the insulation, particularly that used in the motor’s
windings. To guard against insulation damage, some manufacturers
now offer inverter-duty motors having special insulation systems that
resist voltage spike damage. For example, Marathon Motors’s system,
used in all three-phase motors 1 HP and larger, is called MAX GUARD®
(Inverter Rated Insulation System).
Particularly with larger drives, it may be advisable to install line reactors
between the motor and drive to choke off the voltage spikes. In addition,
some increased motor heating will inevitably occur because of the inverter’s
“synthesized” AC wave form. Insulation systems on industrial motors
built in recent years, and especially inverter-duty motors, can tolerate
this except in the most extreme instances. A greater cooling concern
involves operating for an extended time at low motor RPM, which
reduces the flow of cooling air and especially in constant torque applications where the motor is heavily loaded even at low speeds. Here,
secondary cooling such as a special blower may be required.
Constant-speed blower kits
can be added in the field,
providing additional cooling
to motors operated at low
RPM as part of an adjustable
speed drive system.
Routine Maintenance of Electrical Drives
Major maintenance, troubleshooting and repair of drives should be left
to a qualified technician, following the drive manufacturer’s recommendations. However, routine maintenance can help prevent problems.
Here are some tips:
• Periodically check the drive for loose connections or any other
unusual physical conditions such as corrosion.
• Vacuum or brush heatsink areas regularly.
• If the drive’s enclosure is NEMA 1, be sure vent slots are clear of
dust or debris.
• If the drive is mounted within a secondary enclosure, again be sure
vent openings area clear and that any ventilation fans are operating
• Unless it is otherwise necessary for major maintenance or repair, the
drive enclosure should not be opened.
Engineering Data
Temperature Conversion Table
Locate known temperature in °C/°F column.
Read converted temperature in °C/°F column.
°C°C/°F°F °C°C/°F°F °C°C/°F°F
-45.4-50-5815.560 14076.5170338
-42.7-45-4918.365 14979.3175347
-40 -40-4021.170 15882.1180356
-37.2-35-3123.975 16785 185365
-34.4-30-2226.680 17687.6190374
-32.2-25-1329.485 18590.4195383
-5 35
95 20396
205 401
-14 37.810021298.8210410
-23 40.5105221101.6
-32 43.4110230104.4
-41 46.1115239107.2
-50 48.9120248110 230446
-59 51.6125257112.8
-68 54.4130266115.6
-77 57.1135275118.2
-86 60 140284120.9
-95 62.7145293123.7
-12271 160320132.2
-13173.8165329136 275527
°F = (9/5 x °C) + 32
°C = 5/9 (°F - 32)
Mechanical Characteristics
To Find:
Converting Torque Units
Inch-Pounds and Newton Meters
Torque (lb. in.) = 8.85 x Nm
= 88.5 x daNm
HP x 63,025
Torque in Inch-Pounds
Torque (Nm) = lb. in.
Torque (lb. in.) x RPM
Torque (daNm) = lb. in.
120 x Frequency
Number of Poles
Electrical Characteristics
To Find:
SIngle Phase
HP x 746
Knowing HP
E x Eff x PF
kW x 1000
Knowing kW
E x PF
kVA x 1000
Knowing kVAE
Three Phase
HP x 746
1.73 x E x Eff x PF
kW x 1000
1.73 x E x PF
kVA x 1000
1.73 x E
I x E x PF
1.73 x I x E x PF
1.73 x I x E
I x E x Eff x PF
1.73 x I x E x Eff x PF
HP (output)
I = amperes
E = volts
Eff = efficiency
kW - kilowatts
PF = power factor
HP = horsepower
RPM = revolutions per minute
kVA = kilovolt amperes
Fractional/Decimal/Millimeter Conversion
1/64 -.015625-0.397
33/64-.515625 -13.097
1 - .039
1/32 -.03125 -0.794
17/32-.53125 -13.494
2 - .0790
3/64 -.046875-1.191
35/64-.546875 -13.891
3 - .1181
1/16 -.0625 -1.588
9/16 -.5625
4 - .1575
5/64 -.078125-1.984
37/64-.578125 -14.684
5 - .1969
3/32 -.09375 -2.381
19/32-.59375 -15.081
6 - .2362
7/64 -.109375-2.778
39/64-.609375 -15.478
7 - .2756
1/8 -.125
8 - .3150
MM Inch
9/64 -.140625-3.572
41/64-.640625 -16.272
9 - .3543
5/32 -.15625 -3.969
21/32-.65625 -16.669
10 - .3937
43/64-.671875 -17.066
11 - .4331
3/16 -.1875 -4.762
12 - .4724
45/64-.703125 -17.859
13 - .5119
7/32 -.21875 -5.556
23/32-.71875 -18.256
14 - .5519
47/64-.734375 -18.653
15 - .5906
1/4 -.25
16 - .6300
49/64-.765625 -19.447
17 - .6693
9/32 -.28125 -7.144
25/32-.78125 -19.844
18 - .7087
51/64-.796875 -20.241
19 - .7480
5/16 -.3125 -7.938
20 - .7874
53/64-.828125 -21.034
21 - .8268
11/32-.34375 -8.731
27/32-.84375 -21.431
22 - .8661
55/64-.859375 -21.828
23 - .9055
3/8 -.375
24 - .9449
57/64-.890625 -22.622
25 - .9843
13/32-.40625 -10.319
29/32-.90625 -23.019
59/64-.921875 -23.416
7/16 -.4375 -11.112
61/64-.953125 -24.209
15/32-.46875 -11.906
31/32-.96875 -24.606
63/64-.984375 -25.003
1/2 -.5
To convert millimeters to inches, multiply by .03937
To convert inches to millimeters, multiply by 25.40
Actuator: A device that creates mechanical motion by converting
various forms of energy to rotating or linear mechanical energy.
Adjustable Speed Drive: A mechanical, fluid or electrical device that
variably changes an input speed to an output speed matching operating
AGMA (American Gear Manufacturers Association): Standards
setting organization composed of gear products manufacturers and
users. AGMA standards help bring uniformity to the design and
application of gear products.
Air-Over (AO): Motors for fan or blower service that are cooled by the
air stream from the fan or blower.
Alternating Current (AC): The standard power supply available from
electric utilities.
Ambient Temperature: The temperature of the air which, when
coming into contact with the heated parts of a motor, carries off its
heat. Ambient temperature is commonly known as room temperature.
Ampere (Amp): The standard unit of electric current. The current produced by a pressure of one volt in a circuit having a resistance of one ohm.
• The rotating part of a brush-type direct current motor.
• In an induction motor, the squirrel cage rotor.
Axial Movement: Often called “endplay.” The endwise movement of
motor or gear shafts. Usually expressed in thousandths of an inch.
Back Driving: Driving the output shaft of a gear reducer – using it to
increase speed rather than reduce speed. Worm gear reducers are not
suitable for service as speed increasers.
Backlash: Rotational movement of a gear reducer’s output shaft
clockwise and counter clockwise, while holding the input shaft stationary.
Usually expressed in thousandths of an inch and measure at a specific
radius at the output shaft.
Sleeve: Common in home-appliance motors.
Ball: Used when high shaft load capacity is required. Ball bearings
are usually used in industrial and agricultural motors.
Roller: Use on output shafts of heavy-duty gear reducers and on some high-horsepower motors for maximum overhung and thrust load capacities.
Breakdown Torque: The maximum torque a motor can achieve with
rated voltage applied at rated frequency, without a sudden drop in
speed or stalling.
Brush: Current-conducting material in a DC motor, usually graphite, or
a combination of graphite and other materials. The brush rides on the
commutator of a motor and forms an electrical connection between the
armature and the power source.
Canadian Standards Association (CSA): The agency that sets safety
standards for motors and other electrical equipment used in Canada.
Capacitance: As the measure of electrical storage potential of a
capacitor, the unit of capacitance is the farad, but typical values are
expressed in microfarads.
Capacitor: A device that stores electrical energy. Used on single-phase
motors, a capacitor can provide a starting “boost” or allow lower current during operation.
Center Distance: A basic measurement or size reference for worm gear
reducers, measured from the centerline of the worm to the centerline
of the worm wheel.
Centrifugal Starting Switch: A mechanism that disconnects the starting
circuit of a motor when the rotor reaches approximately 75% of operating speed.
Cogging: Non-uniform or erratic rotation of a direct current motor. It
usually occurs at low speeds and may be a function of the adjustable
speed control or of the motor design.
Commutator: The part of a DC motor armature that causes the electrical
current to be switched to various armature windings. Properly sequenced
switching creates the motor torque. The commutator also provides the
means to transmit electrical current to the moving armature through
brushes that ride on the commutator.
Counter Electromotive Force: Voltage that opposes line voltage
caused by induced magnetic field in a motor armature or rotor.
Current, AC: The power supply usually available from the electric
utility company or alternators.
Current, DC: The power supply available from batteries, generators
(not alternators), or a rectified source used for special applications.
Duty Cycle: The relationship between the operating time and the
resting time of an electric motor. Motor ratings according to duty are:
• Continuous duty, the operation of loads for over one hour.
• Intermittent duty, the operation during alternate periods of load and
rest. Intermittent duty is usually expressed as 5 minutes, 30 minutes or
one hour.
Efficiency: A ratio of the input power compared to the output, usually
expressed as a percentage.
Enclosure: The term used to describe the motor housing. The most
common industrial types are: Open Drip Proof (ODP), Totally Enclosed
Fan Cooled (TEFC), Totally Enclosed Non-Ventilated (TENV), Totally
Enclosed Air Over (TEAO). (See Chapter IV for additional information).
Endshield: The part of a motor that houses the bearing supporting the
rotor and acts as a protective guard to the internal parts of the motor;
sometimes called endbell, endplate or end bracket.
Excitation: The act of creating magnetic lines of force from a motor
winding by applying voltage.
Explosion-Proof Motors: These motors meet Underwriters Laboratories
and Canadian Standards Association standards for use in hazardous
(explosive) locations, as indicated by the UL label affixed to the motor.
Locations are considered hazardous because the atmosphere does or
may contain gas, vapor, or dust in explosive quantities.
Field: The stationary part of a DC motor, commonly consisting of permanent magnets. Sometimes used also to describe the stator of an AC
Flanged Reducer: Usually used to refer to a gear reducer having
provisions for close coupling of a motor either via a hollow (quill) shaft
or flexible coupling. Most often a NEMA C face motor is used.
Foot-Pound: Energy required to raise a one-pound weight against the
force of gravity the distance of one foot. A measure of torque. Inchpound is also commonly used on smaller motors and gear reducers. An
inch-pound represents the energy needed to lift one pound one inch;
an inch-ounce represents the energy needed to lift one ounce one inch.
Form Factor: Indicates how much AC component is present in the DC
output from a rectified AC supply. Unfiltered SCR (thyristor) drives have
a form factor (FF) of 1.40. Pure DC, as from a battery, has a form factor
of 1.0. Filtered thyristor and pulse width modulated drives often have
a form factor of 1.05.
Frame: Standardized motor mounting and shaft dimensions as established by NEMA or IEC.
Frequency: Alternating electric current frequency is an expression of
how often a complete cycle occurs. Cycles per second describe how many
complete cycles occur in a given time increment. Hertz (hz) has been
adopted to describe cycles per second so that time as well as number
of cycles is specified. The standard power supply in North America is 60
hz. Most of the rest of the world has 50 hz power.
Full Load Amperes (FLA): Line current (amperage) drawn by a motor
when operating at rated load and voltage on motor nameplate.
Important for proper wire size selection, and motor starter or drive
selection. Also called full load current.
Full Load Torque: The torque a motor produces at its rated horsepower and full-load speed.
Fuse: A piece of metal, connected in the circuit to be protected, that
melts and interrupts the circuit when excess current flows.
Generator: Any machine that converts mechanical energy into electrical energy.
Grounded Circuit:
• An electrical circuit coupled to earth ground to establish a reference
• A malfunction caused by insulation breakdown, allowing current flow
to ground rather than through the intended circuit.
Hertz: Frequency, in cycles per second, of AC power; usually 60 hz in
North America, 50 hz in the rest of the world. Named after H. R. Hertz,
the German scientist who discovered electrical oscillations.
High Voltage Test: Application of a voltage greater than the working
voltage to test the adequacy of motor insulation; often referred to as
high potential test or “hi-pot.”
Horsepower: A measure of the rate of work. 33,000 pounds lifted one
foot in one minute, or 550 pounds lifted one foot in one second. Exactly
746 watts of electrical power equals one horsepower. Torque and RPM
may be used in relating to the horsepower of a motor. For fractional
horsepower motors, the following formula may be used.
HP = T (in.-oz) x 9.917 x N x 107
HP = horsepower
T =Torque
N = revolutions per minute
Hysteresis: The lagging of magnetism in a magnetic metal, behind the
magnetizing flux which produces it.
IEC (International Electrotechnical Commission): The worldwide organization that promotes international unification of standards or norms.
Its formal decisions on technical matters express, as nearly as possible,
an international consensus.
IGBT: Stands for isolated gate bipolar transistor. The most common
and fastest-acting semiconductor switch used in pulse width modulated
(PWM) AC drives.
Impedance: The total opposition in an electric circuit to the flow of an
alternating current. Expressed in ohms.
Induction Motor: The simplest and most rugged electric motor, it
consists of a wound stator and a rotor assembly. The AC induction motor
is named because the electric current flowing in its secondary member
(the rotor) is induced by the alternating current flowing in its primary member (the stator). The power supply is connected only to the stator. The
combined electromagnetic effects of the two currents produce the force
to create rotation.
Insulation: In motors, classified by maximum allowable operating temperature. NEMA classifications include: Class A = 105°C, Class B =
130°C, Class F = 155°C and Class H = 180°C.
Input Horsepower: The power applied to the input shaft of a gear
reducer. The input horsepower rating of a reducer is the maximum
horsepower the reducer can safely handle.
Integral Horsepower Motor: A motor rated one horsepower or larger
at 1800 RPM. By NEMA definitions, this is any motor having a three digit
frame number, for example, 143T.
Inverter: An electronic device that changes direct current to alternating
current; in common usage, an AC drive.
Kilowatt: A unit of power equal to 1000 watts and approximately equal
to 1.34 horsepower.
Load: The work required of a motor to drive attached equipment.
Expressed in horsepower or torque at a certain motor speed.
Locked Rotor Current: Measured current with the rotor locked and
with rated voltage and frequency applied to the motor.
Locked Rotor Torque: Measured torque with the rotor locked and with
rated voltage and frequency applied to the motor.
Magnetic Polarity: Distinguishes the location of north and south poles
of a magnet. Magnetic lines of force emanate from the north pole of a
magnet and terminate at the south pole.
Mechanical Rating: The maximum power or torque a gear reducer
can transmit. Many industrial reducers have a safety margin equal to
200% or more of their mechanical rating, allowing momentary overloads
during start-up or other transient overloads.
Motor Types: Classified by operating characteristics and/or type of
power required. The AC induction motor is the most common. There
are several kinds of AC (alternating current) induction motors, including, for single-phase operation: shaded pole, permanent split
capacitor (PSC), split phase, capacitor start/induction run and capacitor
start/capacitor run. Polyphase or three-phase motors are used in larger
applications. Direct current (DC) motors are also common in industry
as are gearmotors, brakemotors and other types. (See Chapter III for
additional details).
Mounting: The most common motor mounts include: rigid base, resilient base C face or D flange, and extended through bolts. (See Chapter
IV for additional details). Gear reducers are similarly base-mounted,
flange-mounted, or shaft-mounted.
National Electric Code (NEC): A safety code regarding the use of
electricity. The NEC is sponsored by the National Fire Protection
Institute. It is also used by insurance inspectors and by many government bodies regulating building codes.
NEMA (National Electrical Manufacturers Association): A nonprofit trade organization, supported by manufacturers of electrical
apparatus and supplies in the United States. Its standards alleviate
misunderstanding and help buyers select the proper products. NEMA
standards for motors cover frame sizes and dimensions, horsepower
ratings, service factors, temperature rises and various performance
Open Circuit: A break in an electrical circuit that prevents normal current flow.
Output Horsepower: The amount of horsepower available at the output
shaft of a gear reducer. Output horsepower is always less than the input
horsepower due to the efficiency of the reducer.
Output Shaft: The shaft of a speed reducer assembly that is connected
to the load. This may also be called the drive shaft or the slow speed
Overhung Load: A force applied at right angles to a shaft beyond the
shaft’s outermost bearing. This shaft-bending load must be supported
by the bearing.
Phase: The number of individual voltages applied to an AC motor. A
single-phase motor has one voltage in the shape of a sine wave applied
to it. A three-phase motor has three individual voltages applied to
it. The three phases are at 120 degrees with respect to each other so
that peaks of voltage occur at even time intervals to balance the power
received and delivered by the motor throughout its 360 degrees of
Plugging: A method of braking a motor that involves applying partial
or full voltage in reverse to bring the motor to zero speed.
Polarity: As applied to electric circuits, polarity indicates which terminal
is positive and which is negative. As applied to magnets, it indicates
which pole is north and which pole is south.
Poles: Magnetic devices set up inside the motor by the placement and
connection of the windings. Divide the number of poles into 7200 to
determine the motor’s normal speed. For example, 7200 divided by 2
poles equals 3600 RPM.
Power Factor: The ratio of “apparent power” (expressed in kVA) and
true or “real power” (expressed in kW).
Real Power
Power Factor =
Apparent power is calculated by a formula involving the “real power,”
that which is supplied by the power system to actually turn the motor, and
“reactive power,” which is used strictly to develop a magnetic field within
the motor. Electric utilities prefer power factors as close to 100% as
possible, and sometimes charge penalties for power factors below 90%.
Power factor is often improved or “corrected” using capacitors. Power
factor does not necessarily relate to motor efficiency, but is a component of total energy consumption.
Prime Mover: In industry, the prime mover is most often an electric
motor. Occasionally engines, hydraulic or air motors are used. Special
application considerations are called for when other than an electric
motor is the prime mover.
Pull Out Torque: Also called breakdown torque or maximum torque,
this is the maximum torque a motor can deliver without stalling.
Pull Up Torque: The minimum torque delivered by a motor between
zero and the rated RPM, equal to the maximum load a motor can
accelerate to rated RPM.
Pulse Width Modulation: Abbreviated PWM, the most common
frequency synthesizing system in AC drives; also used in some DC drives
for voltage control.
Reactance: The opposition to a flow of current other than pure
resistance. Inductive reactance is the opposition to change of current
in an inductance (coil of wire). Capacitive reactance is the opposition to
change of voltage in a capacitor.
Rectifier: A device or circuit for changing alternating current (AC) to
direct current (DC).
Regenerative Drive: A drive that allows a motor to provide both
motoring and braking torque. Most common with DC drives.
Relay: A device having two separate circuits, it is constructed so that a
small current in one of the circuits controls a large current in the other
circuit. A motor starting relay opens or closes the starting circuit under
predetermined electrical conditions in the main circuit (run winding).
Reluctance: The characteristics of a magnetic field which resist the flow
of magnetic lines of force through it.
Resistor: A device that resists the flow of electrical current for the
purpose of operation, protection or control. There are two types of
resistors - fixed and variable. A fixed resistor has a fixed value of ohms
while a variable resistor is adjustable.
Rotation: The direction in which a shaft turns is either clockwise (CW) or
counter clockwise (CCW). When specifying rotation, also state if viewed
from the shaft or opposite shaft end of motor.
Rotor: The rotating component of an induction AC motor. It is typically constructed of a laminated, cylindrical iron core with slots for castaluminum conductors. Short-circuiting end rings complete the “squirrel
cage,” which rotates when the moving magnetic field induces a current
in the shorted conductors.
SCR Drive: Named after the silicon controlled rectifiers that are at
the heart of these controls, an SCR drive is the most common type of
general-purpose drive for direct current motors.
Self-Locking: The inability of a gear reducer to be driven backwards by
its load. Most general purpose reducers are not self-locking.
Service Factor for Gearing: A method of adjusting a reducer’s load
carrying characteristics to reflect the application’s load characteristics.
AGMA (American Gear Manufacturers Association) has established
standardized service factor information.
Service Factor for Motors: A measure of the overload capacity built
into a motor. A 1.15 SF means the motor can deliver 15% more than the
rated horsepower without injurious overheating. A 1.0 SF motor should
not be loaded beyond its rated horsepower. Service factors will vary for
different horsepower motors and for different speeds.
Short Circuit: A fault or defect in a winding causing part of the normal
electrical circuit to be bypassed, frequently resulting in overheating of
the winding and burnout.
Slip: (1) The difference between rotating magnetic field speed
(synchronous speed) and rotor speed of AC induction motors. Usually
expressed as a percentage of synchronous speed. (2) The difference
between the speed of the rotating magnetic field (which is always
synchronous) and the rotor in a non-synchronous induction motor is know
as slip and is expressed as a percentage of a synchronous speed. Slip
generally increases with an increase in torque.
Speed Regulation: In adjustable speed drive systems, speed regulation
measures the motor and control’s ability to maintain a constant preset
speed despite changes in load from zero to 100%. It is expressed as a
percentage of the drive system’s rated full load speed.
Stator: The fixed part of an AC motor, consisting of copper windings
within steel laminations.
Temperature Rise: The amount by which a motor, operating under
rated conditions, is hotter than its surrounding ambient temperature.
Temperature Tests: These determine the temperature of certain parts
of a motor, above the ambient temperature, while operating under
specific environmental conditions.
Thermal Protector: A device, sensitive to current and heat, which
protects the motor against overheating due to overload or failure to
start. Basic types include automatic rest, manual reset and resistance
temperature detectors.
Thermal Rating: The power or torque a gear reducer can transmit
continuously. This rating is based upon the reducer’s ability to dissipate
the heat caused by friction.
Thermistors: Are conductive ceramic materials, whose resistance remains
relatively constant over a broad temperature range, then changes abruptly
at a design threshold point, creating essentially a solid-state thermal switch.
Attached control modules register this abrupt resistance change and
produce an amplified output signal, usually a contact closure or fault
trip annunciation. Thermistors are more accurate and faster responding
than thermostats.
Thermostat: A protector, which is temperature-sensing only, that is
mounted on the stator winding. Two leads from the device must be
connected to a control circuit, which initiates corrective action. The
customer must specify if the thermostats are to be normally closed or
normally open.
Thermocouple: A pair of dissimilar conductors joined to produce a
thermoelectric effect and used to accurately determine temperature.
Thermocouples are used in laboratory testing of motors to determine
the internal temperature of the motor winding.
Thrust Load: Force imposed on a shaft parallel to a shaft’s axis. Thrust
loads are often induced by the driven machine. Be sure the thrust load
rating of a gear reducer is sufficient so that its shafts and bearings can
absorb the load without premature failure.
Torque: The turning effort or force applied to a shaft, usually expressed
in inch-pounds or inch-ounces for fractional and sub-fractional HP
Starting Torque: Force produced by a motor as it begins to turn from
standstill and accelerate (sometimes called locked rotor torque).
Full-Load Torque: The force produced by a motor running at rated
full-load speed at rated horsepower.
Breakdown Torque: The maximum torque a motor will develop
under increasing load conditions without an abrupt drop in speed
and power. Sometimes called pull-out torque.
Pull-Up Torque: The minimum torque delivered by a motor between
zero and the rated RPM, equal to the maximum load a motor can
accelerate to rated RPM.
Transformer: Used to isolate line voltage from a circuit or to change
voltage and current to lower or higher values. Constructed of primary
and secondary windings around a common magnetic core.
Underwriters Laboratories (UL): Independent United States testing
organization that sets safety standards for motors and other electrical
Vector Drive: An AC drive with enhanced processing capability that
provides positioning accuracy and fast response to speed and torque
changes. Often used with feedback devices in a closed-loop system.
Voltage: A unit of electromotive force that, when applied to conductors, will produce current in the conductors.
Watt: The amount of power required to maintain a current of 1 ampere
at a pressure of one volt when the two are in phase with each other. One
horsepower is equal to 746 watts.
Winding: Typically refers to the process of wrapping coils of copper
wire around a core. In an AC induction motor, the primary winding is a
stator consisting of wire coils inserted into slots within steel laminations.
The secondary winding of an AC induction motor is usually not a winding
at all, but rather a cast rotor assembly. In a permanent magnet DC
motor, the winding is the rotating armature.
Please Read Carefully
This Basic Training Manual is not intended as a design guide for
selecting and applying Marathon Motors electric motors, gear drive
products, or adjustable frequency drives. It is intended as a general
introduction to the concepts and terminology used with the products
offered by Marathon Motors. Selection, application, and installation
of Marathon Motors electric motors, gearmotors, and drives should be
made by qualified personnel.
General Installation & Operating Instructions are provided with all
Marathon Motors motors, gearmotors, and drives. These products should
be installed and operated according to those instructions. Electrical
connections should be made by a licensed electrician. Mechanical
installation should be done by a mechanical contractor or maintenance
engineer that is familiar with installing this type of equipment. Injury
to personnel and/or premature, and possibly catastrophic, equipment
failure may result from improper installation, maintenance, or operation.
Marathon Motors makes no warranties or representations, express or
implied, by operation of law or otherwise, as to the merchantability or
fitness for a particular purpose of the goods sold as a result of the use
of this information. The Buyer acknowledges that it alone has determined that the goods purchased will suitably meet the requirements
of their intended use. In no event will Marathon Motors be liable for
consequential, incidental, or other damages the result from the proper
or improper application of this equipment.
MARATHON MOTORS Basic Training Manual
100 E. Randolph Street
PO Box 8003
Wausau, WI 54401-8003
PH: 715-675-3311
A Regal Brand
©2013 Regal-Beloit Corporation BROCHURE SB800 7572M/BH/10-13/1K/QG Printed in the USA
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