Basic Training for Motors, Gears and Drives
BASIC TRAINING
MOTORS, GEARS & DRIVES
INDUSTRIAL-DUTY & COMMERCIAL-DUTY
Electric Motors
Gear Reducers
Gearmotors
AC & DC Drives
Basic Training
Industrial-Duty & Commercial-Duty
Electric Motors
Gearmotors
Gear Reducers
AC & DC Drives
A Publication Of
Copyright ©1999
Price $20.00
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Contents
I.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Electric Motor History and Principles
II.
General Motor Replacement Guidelines . . . . . . . . . . . .7
III.
Major Motor Types . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
AC Single Phase
AC Polyphase
Direct Current (DC)
Gearmotors
Brakemotors
Motors For Precise Motor Control
IV.
Mechanical Considerations . . . . . . . . . . . . . . . . . . . . .16
Enclosures and Environment
NEMA Frame/Shaft Sizes
NEMA Frame Suffixes
Frame Prefixes
Mounting
V.
Electrical Characteristics
and Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Voltage
Phase
Current
Frequency
Horsepower
Speeds
Insulation Class
Service Factor
Capacitors
Efficiency
Thermal Protection (Overload)
Individual Branch Circuit Wiring
Reading a LEESON Model Number
Major Motor Components
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VI.
Metric (IEC) Designations . . . . . . . . . . . . . . . . . . . . . .34
VII.
Motor Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Lubrication Procedure
Relubrication Interval Chart
VIII. Common Motor Types and
Typical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . .41
IX.
Gear Reducers and Gearmotors . . . . . . . . . . . . . . . . .46
Right-Angle Worm Gear Reducers
Parallel-Shaft Gear Reducers
Gearmotors
Installation and Application Considerations
Special Environmental Considerations
Gear Reducer Maintenance
X.
Adjustable Speed Drives . . . . . . . . . . . . . . . . . . . . . . .55
DC Drives
AC Drives
“One Piece” Motor/Drive Combinations
AC Drive Application Factors
Motor Considerations With AC Drives
Routine Maintenance of Electrical Drives
XI.
Engineering Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Temperature Conversion Table
Mechanical Characteristics Table
Electrical Characteristics Table
XII.
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
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CHAPTER I
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 currentcarrying 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 AC motors are produced by
LEESON and many other manufacturers. In polyphase motors, the place-4-
ment 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.
In recent years, 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 systems.
LEESON Electric also produces permanent-magnet direct current motors.
The DC motor is the oldest member of the electric motor family. Recent
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. LEESON 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
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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 95% 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.
The Doerr family, whose members founded and continue to own and operate
LEESON Electric, has a three-generation history in electric motor manufacturing.
Shown at left is a motor from the early 1900s, made by St. Louis Electrical Works,
later Baldor Electric. At right is a motor from the late 1930s, made by Electro
Machines, later Doerr Electric and now part of Emerson Electric.
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CHAPTER II
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.
Selection
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:
•
•
•
•
Nameplate Data
Mechanical Characteristics
Motor Types
Electrical Characteristics and Connections
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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.
Nameplate
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
•
Catalog number.
•
Motor model number.
•
Frame.
•
Type (classification varies from manufacturer to manufacturer).
•
Phase - single, three or direct current.
•
HP - horsepower at rated full load speed.
•
HZ - frequency in cycles per second. Usually 60 hz in United States,
50 hz overseas.
•
RPM - revolutions per minute.
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•
Voltage.
•
Amperage (F.L.A.) - full load motor current.
•
Maximum ambient temperature in centigrade - usually +40°C (104°F).
•
Duty - most motors are rated continuous. Some applications, however, may use motors designed for intermittent, special, 15, 30 or 60
minute duty.
•
NEMA electrical design - B, C and D are most common. Design letter
represents the torque characteristics of the motor.
•
Insulation class - standard insulation classes are B, F, and H. NEMA has
established safe maximum operating temperatures for motors. This
maximum temperature is the sum of the maximum ambient and maximum rise at maximum ambient.
•
Code - indicates locked rotor kVA per horsepower.
•
Service factor - a measure of continuous overload capacity.
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CHAPTER III
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.
PSC (Permanent Split Capacitor) 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-to-start belt
drive fans and blowers, as well as light-start
pump applications.
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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 lightstart 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.
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A heavy-duty polyphase motor with cast-iron frame.
AC Polyphase
Polyphase
(three-phase) 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.
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Design E
Normal locked rotor
torque and current,
low slip
Design D
High locked rotor
torque and high slip
75-190
275
200-285
70-275
Design B
Normal locked rotor
torque and normal
locked rotor current
Design C
High locked rotor
torque and normal
locked rotor current
70-275
Locked
Rotor
Torque
(Percent
Rated Load
Torque)
Design A
High locked rotor
torque and high
locked rotor current
Polyphase
Characteristics
60-140
NA
140-195
65-190
65-190
Pull-Up
Torque
(Percent
Rated Load
Torque)
160-200
275
190-225
175-300
175-300
Breakdown
Torque
(Percent
Rated Load
Torque)
800-1000
600-700
600-700
600-700
Not
defined
Locked
Rotor
Current
(Percent
Rated
Load
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
required
Fans, blowers, centrifugal pumps
0.5-3% and compressors, motor-generator
sets, etc., where starting torque
requirements are relatively low
5-8%
1-5%
High
Low
Medium
Medium or
high
Fans, blowers, centrifugal pumps
0.5-5% and compressors, motor-generator
sets, etc., where starting torque
requirements are relatively low
Relative
Efficiency
Medium or
high
Typical Applications
Fans, blowers, centrifugal pumps
0.5-5% and compressors, motor-generator
sets, etc., where starting torque
requirements are relatively low
Slip
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 speed/torque 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.
Gearmotors
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.
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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 subfractional 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.
Brakemotors
A brakemotor is a pre-connected package of industrial-duty motor and failsafe, 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 fancooled 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.
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CHAPTER IV
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.
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Explosion Proof motors meet Under-writers 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 in explosive
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
Acetylene
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
Aluminum, magnesium and other metal
dusts with similar characteristics
Group F
Carbon black, coke or coal dust
Group G
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. LEESON explosion
proof motors are approved for all classes noted except
Class I, Groups A & B .
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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.
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-19-
3
3 1/2
3 1/2
4 1/2
5 1/4
6 1/4
7
8
9
10
11
S56
56
143T
145T
182T
184T
S213T
213T
215T
254T
256T
284TS
284T
286TS
286T
324TS
324T
326TS
326T
364TS
364T
365TS
365T
404TS
404T
405TS
405T
444TS
444T
445T
447TZ
9
8
7
6 1/4
5 1/2
5
4 1/4
3 3/4
2 3/4
2 7/16
2 1/8
1 3/4
E
7 1/4
7 1/4
8 1/4
10
6 7/8
6 1/8
6 1/8
5 5/8
6
5 1/4
5 1/2
4 3/4
4 1/8
5
2 3/4
2 3/4
3 1/2
2 1/4
2 3/4
2
2 1/2
1 1/2
1 3/8
27/32
F
H
13/16
13/16
21/32
21/32
17/32
17/32
13/32
13/32
11/32
11/32
Slot
9/32
Slot
11/32
Slot
—
—
—
—
—
—
—
3 1/2
2 7/8
2 3/8
1 15/16
1 9/16
1 1/4
N
8 15/32
8 15/32
6 19/32
5 19/32
6 19/32
5 19/32
4 7/8
P
22 1/4
19 5/16
17 13/16
15 3/4
14 1/2
12 15/16
22
19 1/8
17 3/8
15 3/4
14 3/4
13 1/4
10 11/16 10 13/16
9 15/16
8 3/4
6 13/16
6 5/16
6 13/16
5 13/16
5 1/16
O
3 3/8
2 3/8
2 1/8
2 7/8
2 1/8
2 7/8
1 7/8
2 3/8
1 7/8
2 3/8
1 7/8
2 1/8
1 7/8
2 1/8
1 5/8
1 7/8
1 5/8
1 7/8
1 5/8
1 3/8
1 1/8
7/8
5/8
1/2
3/8
U
4 3/4
8 1/2
8 1/2
10 1/8
4 1/4
7 1/4
4 1/4
7 1/4
3 3/4
5 7/8
3 3/4
5 7/8
3 3/4
5 1/4
3 3/4
5 1/4
3 1/4
4 5/8
3 1/4
4 5/8
4
3 3/8
2 3/4
2 1/4
1 7/8
1 1/2
1 1/8
N-W
3
3
3
2
1 1/2
1 1/4
1
3/4
3/4
3/4
1/2
1/2
3/8
AA
21 11/16
16 5/16
15 7/16
13 1/2
11 3/4
11 5/8
8 5/16
6 3/8
6 3/8
5 5/16
4 7/8
5 5/16
4 7/8
4 1/2
AB
8 1/4
4
7
4
7
3 1/2
5 5/8
3 1/2
5 5/8
3 1/2
5
3 1/2
5
3
4 3/8
3
4 3/8
3 3/4
3 1/8
2 5/8
2 1/8
2 1/16
1 11/16
1 5/16
AH
14
11
11
11
9
7 1/4
7 1/4
7 1/4
5 7/8
5 7/8
3 3/4
3 3/4
AJ
16
12 1/2
12 1/2
12 1/2
10 1/2
8 1/2
8 1/2
8 1/2
4 1/2
4 1/2
3
3
AK
7 1/2
6 5/8
5 7/8
5 1/4
4 3/4
*4 1/4
*3 1/2
*2 3/4
*2 1/4
2 3/4
2 1/2
2 1/16
BA
1/4
1/4
1/4
1/4
1/4
1/4
1/4
1/4
1/8
1/8
1/8
1/8
BB
18
15 1/2
14
13 3/8
11
9 5/8
9
8 7/8
8 7/8
6 1/2
6 1/2
5
4 7/8
BD
—
—
—
—
—
—
2 1/4
2 1/4
2 1/4
2 1/4
2 1/4
1 5/8
XO
19 3/8
19 3/8
17/3/4
15 3/4
14 1/2
12 7/8
11 3/32
9 3/32
9 3/32
7 5/32
5 7/8
7 5/32
5 7/8
5 1/8
XP
5/8 11
5/8 11
5/8 11
5/8 11
1/2 13
1/2-13
1/2-13
1/2-13
3/8-16
3/8-16
1/4-20
1/4-20
TAP
**
5/8
7/8
7/8
7/8
1/2
3/4
1/2
3/4
5/8
1/2
5/8
1/2
1/2
1/2
3/8
1/2
3/8
3/8
5/16
5/16
3/16
3/16
3/64 Flat
3/64 Flat
KEY
Shaded area denotes dimensions established by NEMA standard MG-1. Other dimensions will vary among manufactures.
2 5/8
48
D
42
NEMA
Frame
Size ▲
Motor Frame Dimensions
(inches)
NEMA Frame Suffixes
C
D
=
=
H
=
J
JM
=
=
JP
=
M
N
T,TS
=
=
=
TS
=
Y
=
Z
=
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
Close-coupled pump motor with specific dimensions and
bearings
Close-coupled pump motor with specific dimensions and
bearings
63/4” flange (oil burner)
71/4” flange (oil burner)
Integral horsepower NEMA standard shaft dimensions if
no additional letters follow the “T” or “TS”.
Motor with NEMA standard “short shaft” for beltdriven 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. For example, the letter
in front of LEESON’s frame number, L56, indicates the overall length of the
motor.
Mounting
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.
-20-
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 LEESON.
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.
-21-
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 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.
Drive
Multiplier
Flat belt*
Timing belt+
Chain sprocket
Spur gear
Helical gear
1.33
0.9
0.7
0.75
0.85
* This multiplier is intended for use with conventional single-ply flat belts.
When other than single-ply flat 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 that necessary to avoid belt slap or tooth
jumping.
-22-
Belt Tensioning
Manufacturers of belts can provide recommended tensioning values and
instruments for precisely determining belt tension. Particularly in very
high-speed, very high-torque or very high-horsepower applications, critical
belt tensioning can be important. For most industrial applications, however, these general belt tensioning procedures are usually adequate:
1.
2.
3.
4.
The best tension is typically the lowest at which the belt will not slip
under peak load.
Over-tensioning will shorten belt and bearing life.
After installing a new belt, check the tension often during the first 24
to 48 operating hours, and re-tension as necessary.
Periodically inspect and re-tension the belt.
As a general rule, the correct belt tension can be gauged by deflecting the
belt at mid-span with your thumb while the motor is stopped. You should
be able to deflect approximately 1/2 inch with light to moderate pressure
on single-ribbed belts. Multiple ribs will require additional pressure.
Two methods of checking belt tension while the motor is operating include
visually assessing whether there is any belt flutter, or listening for belt
squeal. Either can occur as a result of inadequate tension.
-23-
CHAPTER V
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%.
Voltage
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 motor.
Phase
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.
-24-
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.
Horsepower
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 =
84,000
Torque (in/lbs) x RPM
HP =
63,000
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:
2
4
6
8
Pole
Pole
Pole
Pole
60 hz
3450
1725
1140
850
50 hz
2850
1425
950
700
Synch. Speed
3600
1800
1200
900
Synchronous speed (no-load) can be determined by this formula:
Frequency (Hertz) x 120
Number of Poles
-25-
Insulation Class
Insulation systems are rated by standard NEMA classifications according to
maximum allowable operating temperatures. They are as follows:
Class
Maximum Allowed Temperature*
A
105°C
(221°F)
B
130°C
(266°F)
F
155°C
(311°F)
H
180°C
(356°F)
* 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 LEESON 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.
-26-
For easy reference, standard NEMA service factors for various horsepower
motors and motor speeds are shown in this table.
FOR DRIP PROOF MOTORS
Service Factor Synchronous Speed (RPM)
HP
/6, 1/4, 1/3
1/
2
3/
4
1
11/2 up
1
3600
1800
1200
900
1.35
1.25
1.25
1.25
1.15
1.35
1.25
1.25
1.15
1.15
1.35
1.25
1.15
1.15
1.15
1.35
1.25
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
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.
Efficiency
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 heat.
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.
-27-
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 manual-reset 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.
Individual Branch Circuit Wiring
All wiring and electrical connections should comply with the National
Electrical Code (NEC) and with local codes and practices. Undersized wire
between the motor and the power source will limit the starting and load
carrying abilities of the motor. The recommended copper wire and transformer sizes are shown in the following charts.
Single Phase Motors - 230 Volts
Distance – Motor to Transformer (Feet)
HP
kVA
100
150
200
300
500
1.5
3
10
8
8
6
4
2
3
10
8
8
6
4
3
5
8
8
6
4
2
5
7.5
6
4
4
2
0
7.5
10
6
4
3
1
0
-28-
WIRE GAGE
Transformer
Three Phase Motors - 230 & 460 Volts
Distance – Motor to Transformer (Feet)
HP
Volts
kVA
100
150
200
300
500
1.5
230
3
12
12
12
12
10
1.5
460
3
12
12
12
12
12
2
230
3
12
12
12
10
8
2
460
3
12
12
12
12
12
3
230
5
12
10
10
8
6
3
460
5
12
12
12
12
10
5
230
7.5
10
8
8
6
4
5
460
7.5
12
12
12
10
8
7.5
230
10
8
6
6
4
2
7.5
460
10
12
12
12
10
8
10
230
15
6
4
4
4
1
10
460
15
12
12
12
10
8
15
230
20
4
4
4
2
0
15
460
20
12
10
10
8
6
20
230
4
2
2
1
0
20
460
10
8
8
6
4
25
230
2
2
2
0
0
8
8
6
6
4
Consult
Local
25
460
30
230
Power
2
1
1
0
0
30
460
Company
8
6
6
4
2
40
230
1
0
0
0
0
40
460
6
6
4
2
0
50
230
1
0
0
0
0
50
460
4
4
2
2
0
30
230
1
0
0
0
0
60
460
4
2
2
0
0
75
230
0
0
0
0
0
75
460
4
2
2
0
0
-29-
WIRE GAGE
Transformer
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.
Full-voltage starters, also called across-the-line starters, apply full line voltage directly to the motor, either through manual or magnetic contacts.
Magnetic starters are used on larger horsepowers. Reversing starters, which
allow the switching of two leads to change motor rotation, are also usually magnetic.
Reduced-voltage starters, also called soft-starts, apply less than full voltage
during the starting sequence of a motor. This reduces current and torque
surges, easing the strain on power supply systems and driven devices.
Resistors, transformers or solid-state devices can achieve this voltage control. In addition, AC drives offer soft-start inherently. (See Chapter X for
complete information on AC drives.)
Both the National Electrical Manufacturers Association (NEMA) and the
International Electrotechnical Commission (IEC) rate starters to aid in
matching them to the motor and application.
-30-
Reading a LEESON 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 LEESON model numbers are configured.
EXAMPLE:
Position No.
1
2
3
4
7
8
9
Sample Model No.
A B
4
C 17 D B
5
6
1
A (A-Z)
10
Position 1: U.L. Prefix
A— Auto protector. U.L. recognized for locked rotor plus run,
also recognized construction (U.L. 1004)*.
M— Manual protector. U.L. recognized for locked rotor plus run,
also recognized construction (U.L. 1004)*.
L— Locked rotor protector (automatic). U.L. recognized for locked rotor
only, also recognized construction (U.L. 1004)*.
C— Component recognition. (U.L. 1004) No protector.
U— Auto protector. Not U.L. recognized.
P— Manual protector. Not U.L. recognized.
T— Thermostat, not U.L. recognized.
N— No overload protection.
*This applies only to 48, S56, and 56 frame designs through 1 HP, Open & TENV.
Position 2: (Optional)
This position is not always used.
M— Sub-Fractional HP Motors.
Z— BISSC Approved.
Other— Customer Code
Position 3: Frame
4 - 48 Frame
6 - 56 Frame
42 - 42 Frame
143 - 143T Frame
145 - 145T Frame
182 - 182T Frame
184 - 184T Frame
213 - 213T Frame
215 - 215T Frame
Position 4: Motor Type
C— Cap. Start/Ind. Run
D— Direct Current
K— Cap. Start/Cap. Run
P— Permanent Split
S— Split Phase
23 - 23 Frame
30 - 30 Frame
34 - 34 Frame
36 - 36 Frame
38 - 38 Frame
39 - 39 Frame
40 - 40 Frame
43 - 43 Frame
44 - 44 Frame
53 - 53 Frame
65 - 65 Frame
Position 6: Enclosure
D— Drip-Proof
E— Explosion-Proof TENV
F— Fan Cooled
N— TENV
O— Open
S— Splashproof
W— Weatherproof, Severe Duty, Chemical Duty,
WASHGUARD™ - TEFC
X— Explosion-Proof TEFC
V— Weatherproof, Severe Duty, Chemical Duty,
WASHGUARD™ - TENV
Position 7: Mounting
B— Rigid base standard
C— “C” face - no base - NEMA
D— “D” flange - no base - NEMA
H— 48 frame - 56 frame mounting/shaft rigid
J— 48 frame - 56 frame mounting/shaft resilient
K— Rigid mount with “C” flange
L— Rigid mount with “D” flange
M— Motor parts - rotor and stator
R— Resilient base
S— Shell motor
T— Torpedo (face-less/base-less)
Z— Special mounting
Position 8: Sequence Number
Number assigned as required when new designs
with new characteristics are needed.
Position 9: Modification Letter
Major modification letter. Used when revisions
made in existing model will affect service parts.
T—Three Phase
B—Brushless DC
H—Hysteresis Sync.
R—Reluctance Sync.
Position 5: RPM
RPM-Single Speed
RPM-Multi-Speed
34 - 3450 RPM 60 Hz 2 Pole
24 - 2 and 4 Poles
28 - 2850 RPM 50 Hz 2 Pole
26 - 2 and 6 Poles
17 - 1725 RPM 60 Hz 4 Pole
82 - 2 and 8 Poles
14 - 1425 RPM 50 Hz 4 Pole
212 - 2 and 12 Poles
11 - 1140 RPM 60 Hz 6 Pole
46 - 4 and 6 Poles
9 - 950 RPM 50 Hz 6 Pole
48 - 4 and 8 Poles
8 - 960 RPM 60 Hz 8 Pole
410 - 4 and 10 Poles
7 - 720 RPM 50 Hz 8 Pole
412 - 4 and 12 Poles
7 - 795 RPM 60 Hz 10 Pole
68 - 6 and 8 Poles
6 - 580 RPM 50 Hz 10 Pole
6 - 580 RPM 60 Hz 12 Pole
Odd frequencies other than 50 Hz show synchronous speed code.
DC and special motors may have one, two, or three digits indicating
motor speed rounded to the nearest hundred RPM.
-31-
Position 10: (Optional)
A date code consisting of either A-Z,
and two digits 00-99.
Major Components of an Electric Motor
Capacitor Case*
Rear Endshield
Fan Guard**
* SINGLE PHASE ONLY
** TEFC ONLY
External
Fan**
Capacitor*
Frame
Stator
Starting
Switch*
(Rotating)
Internal Fan
Shaft
Front Endshield
Starting
Switch*
(Stationary)
Connection
Box
Cast Rotor
Base
Nameplate
Bearing
End Ring
-32-
-33-
CHAPTER VI
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
NOTES
* 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.
-34-
KW/HP** Frame
Assignments
Dimensions in Millimeters
IEC
3 Phase – TEFC
D
E
F
H
U
BA
N-W
56
45
35.5
5.8
9
36
20
–
–
–
NA
–
–
–
–
–
–
–
–
–
–
NA
63
–
50
–
40
–
7
–
11
–
40
–
23
–
42
71
66.7
56
44.5
45
21.4
7
7.1
14
9.5
45
52.4
30
–
.55
3/4
.37
1/2
–
–
48
80
76.2
62.5
54
50
34.9
10
8.7
19
12.7
50
63.5
40
38.1
1.1
1-1/2
.75
1
.55KW
3/4HP
56
90
88.9
70
61.9
50
38.1
10
8.7
24
15.9
56
69.9
50
47.6
1.5
2
1.1
1-1/2
.75
1
56
90
88.9
70
69.8
62.5
50.8
10
8.7
24
22.2
56
57.2
50
57.2
2.2
3
1.5
2
1.1
1-1/2
145T
100
88.9
80
69.8
70
63.5
12
8.7
28
22.2
63
57.2
60
57.2
3
4
2.2
3
1.5
2
182T
112
114.3
95
95.2
57
57.2
12
10.7
28
28
70
70
60
69.9
3.7
5
2.2
3
1.5
2
184T
112
114.3
95
95.2
70
68.2
12
10.7
28
28
70
70
60
69.9
3.7
5
4
5-4/5
2.2
–
213T
132
133.4
108
108
70
69.8
12
10.7
38
34.9
89
89
80
85.7
7.5
10
5.5
7-1/2
3
–
215T
132
133.4
108
108
89
88.8
12
10.7
38
34.9
89
89
80
85.7
–
–
7.5
10
5.5
7-1/2
254T
160
158.8
127
127
105
104.8
15
13.5
42
41.3
108
108
110
101.6
15
20
11
15
7.5
10
256T
160
158.8
127
127
127
127
15
13.5
42
41.3
108
108
110
101.5
18.5
25
15
20
11
15
284T
180
177.8
139.5
139.8
120.5
120.2
15
13.5
48
47.6
121
121
110
117.5
22
–
18.5
25
–
–
286T
180
177.8
139.5
139.8
139.5
139.8
15
13.5
48
47.6
121
121
110
117.5
22
30
22
30
15
20
324T
180
203.3
159
158.8
133.5
133.4
19
16.7
55
54
133
133
110
133.4
30
40
30
40
–
–
326T
200
203.2
159
158.8
152.5
152.4
19
16.7
55
54
133
133
110
133.4
37
50
37
50
22
30
364T
225
228.6
178
117.8
143
142.8
19
16.7
60
60.3
149
149
140
149.2
–
–
37
50/75
30
40
365
225
228.6
178
177.8
155.5
155.6
19
16.7
60
60.3
149
149
140
149.2
45
60/75
45
60/75
37
50
405T
250
254
203
203.2
174.5
174.6
24
20.6
65
73
168
168
140
182.2
55
55
75/100 75/100
–
–
444T
280
279.4
228.5
228.6
184
184.2
24
20.6
75
85.7
190
190
140
215.9
–
–
–
–
45
60/100
445T
280
279.4
228.5
228.6
209.5
209.6
24
20.6
75
85.7
190
190
140
215.9
–
–
–
–
55
75/125
NEMA
56
63
71
80
90S
90L
100L
112L
112M
132S
132M
160M*
160L*
180M*
180L*
200M*
200L*
225S*
225M*
250M*
280S*
280M*
2 Pole
See notes on facing page.
-35-
4 Pole 6 Pole
.25KW .18KW
1/3HP 1/4HP
–
–
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.
Protection Against
Solid Objects
Protection Against
Liquids
No. Definition
No.
Definition
0
No protection.
0
No protection.
1
Protected against solid objects
of over 50mm (e.g. accidental
hand contact).
1
Protected against water
vertically dripping
(condensation).
2
Protected against solid objects
of over 12mm (e.g. finger).
2
Protected against water dripping
up to 15° from the vertical.
3
Protected against solid objects
of over 2.5mm (e.g. tools, wire).
3
Protected against rain falling
at up to 60° from the vertical.
4
Protected against solid objects
of over 1mm (e.g. thin wire).
4
Protected against water splashes
from all directions.
5
Protected against dust.
5
Protected against jets of water
from all directions.
6
Totally protected against dust.
Does not involve rotating
machines.
6
Protected against jets of water
comparable to heavy seas.
7
Protected against the effects of
immersion to depths of between
0.15 and 1m.
8
Protected against the effects of
prolonged immersion at depth.
-36-
IEC Cooling, Insulation and Duty Cycle Indexes
IEC has additional designations indicating how a motor is cooled (two-digit
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.
S1 Continuous 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 rise.
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.
-37-
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.
-38-
CHAPTER VII
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 highquality 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 Shell Dolium R.
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.
-39-
Relubrication Intervals Chart
For Motors Having Grease Fittings
Hours of Service
Per Year
HP Range
Suggested
Relube Interval
5000
1/18 to 7 1/2
10 to 40
50 to 100
5 years
3 years
1 year
Continuous Normal
Applications
to 7 1/2
10 to 40
50 to 100
2 years
1 year
9 months
Seasonal Service Motor is idle for
6 months or more
All
1 year
(beginning of
season)
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.
-40-
CHAPTER VIII
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 available.
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 & TENV
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 three-phase
power is suitable.
Three Phase * NEMA C Face Less Base * ODP
Fans, blowers, compressors, tools and speed reducers.
-41-
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
Torques
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
Phase
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.
-42-
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.
-43-
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 overspeeded by an obstructed auger. Special flange mounts directly to the
auger gear reducer.
Hatchery/Incubator Fan Motor * Band Mounted * Single Phase *
TEAO
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 process.
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.
-44-
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 intermittentduty 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 *
TENV
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 generator-supplied 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.
-45-
CHAPTER IX
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
-46-
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 gearmotors.
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.
-47-
Gearmotors
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. LEESON uses the
term Gear+Motor™ for its separable reducer and motor packages.
At left, a quill-style input worm gear reducer uses a hollow unput 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.
-48-
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.
-49-
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.
-50-
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 LEESON’s, provide a 200% safety margin over this rating for start-ups and momentary overloads. Thermal
-51-
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 divided 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.
-52-
Service Factor Conversions for Reducers
With Electric or Hydraulic Motor Input
Duration of Service
(Hours per day)
Occasional 1/2 Hour
Uniform
Load
Moderate
Shock
Heavy
Shock
Extreme
Shock
--*
--*
1.0
1.25
Less than 3 Hours
1.0
1.0
1.25
1.50
3 - 10 Hours
1.0
1.25
1.50
1.75
Over 10 Hours
1.25
1.50
1.75
2.00
* 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
Motor
Single Cylinder
Engines
Multi-Cylinder
Engines
1.00
1.50
1.25
1.25
1.75
1.50
1.50
2.00
1.75
1.75
2.25
2.00
2.00
2.50
2.25
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.
-53-
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 disassembly.
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.
-54-
CHAPTER X
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.
-55-
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
-56-
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 drive.
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 com-57-
bined with feedback devices such as tachometers, encoders and resolvers
in a closed-loop system, are continuing to replace DC drives in demanding applications.
Encoders can be added to inverter-duty three-phase motors for
use in closed-loop vector drive
systems.
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.
“Sub-micro” drives provide a
wide array of features in a very
small package.
-58-
“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.
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.
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.
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 considered:
-59-
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 rat-
-60-
ings, 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-though” 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 three-phase.
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 codes.
Environmental Factors: The enemies of electronic components are wellknown. 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,
-61-
Speed Setpoint
Drive Status
RUN > 56.00 HZ
Speed Units
Direction (Forward)
Percent Load
Drive Status
RUN > 85%
Direction (Forward)
Speed Setpoint
Drive Status
FAULT: OVERLOAD
Examples of operating and diagnostic displays in a modern AC drive.
-62-
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.
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, LEESON’s system, used in all three-phase
motors 1 HP and larger, is called IRIS™ (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.
-63-
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
properly.
Unless it is otherwise necessary for major maintenance or repair, the
drive enclosure should not be opened.
-64-
CHAPTER XI
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
-58
15.5
60
140
76.5
170
338
-42.7
-45
-49
18.3
65
149
79.3
175
347
-40
-40
-40
21.1
70
158
82.1
180
356
-37.2
-35
-31
23.9
75
167
85
185
365
-34.4
-30
-22
26.6
80
176
87.6
190
374
-32.2
-25
-13
29.4
85
185
90.4
195
383
-29.4
-20
-4
32.2
90
194
93.2
200
392
-26.6
-15
-5
35
95
203
96
205
401
-23.8
-10
-14
37.8
100
212
98.8
210
410
-20.5
-5
-23
40.5
105
221
101.6
215
419
-17.8
-0
-32
43.4
110
230
104.4
220
428
-15
-5
-41
46.1
115
239
107.2
225
437
-12.2
-10
-50
48.9
120
248
110
230
446
-9.4
-15
-59
51.6
125
257
112.8
235
455
-6.7
-20
-68
54.4
130
266
115.6
240
464
-3.9
-25
-77
57.1
135
275
118.2
245
473
-1.1
-30
-86
60
140
284
120.9
250
482
-1.7
-35
-95
62.7
145
293
123.7
255
491
-4.4
-40
-104
65.5
150
302
126.5
260
500
-7.2
-45
-113
68.3
155
311
129.3
265
509
-10
-50
-122
71
160
320
132.2
270
518
-12.8
-55
-131
73.8
165
329
136
275
527
°F = (9/5 x °C) + 32
°C = 5/9 (°F - 32)
-65-
Mechanical Characteristics
Converting Torque Units
Inch-Pounds and Newton Meters
To Find:
Torque (lb. in.) = 8.85 x Nm
Use:
or
Torque in Inch-Pounds
= 88.5 x daNm
HP x 63,025
RPM
Torque (Nm) = lb. in.
8.85
Torque (lb. in.) x RPM
Horsepower
5250
Torque (daNm) = lb. in.
88.5
120 x Frequency
RPM
Number of Poles
Electrical Characteristics
Use:
SIngle Phase
To Find:
Or:
Three Phase
Amperes
HP x 746
HP x 746
Knowing HP
E x Eff x PF
1.73 x E x Eff x PF
Amperes
kW x 1000
kW x 1000
Knowing kW
E x PF
1.73 x E x PF
Amperes
kVA x 1000
kVA x 1000
Knowing kVA
E
1.73 x E
Kilowatts
I x E x PF
1.73 x I x E x PF
1000
1000
kVA
HP (output)
IxE
1.73 x I x E
1000
1000
I x E x Eff x PF
1.73 x I x E x Eff x PF
746
746
I = amperes
E = volts
Eff = efficiency
kW - kilowatts
PF = power factor
HP = horsepower
RPM = revolutions per minute
kVA = kilovolt amperes
-66-
Fractional/Decimal/Millimeter Conversion
Fraction
MM
Inch
1/64
- .015625 - 0.397
Decimal
Millimeter
33/64 - .515625
- 13.097
1
- .039
1/32
- .03125
17/32 - .53125
- 13.494
2
- .0790
3/64
- .046875 - 1.191
35/64 - .546875
- 13.891
3
- .1181
1/16
- .0625
9/16
- 14.288
4
- .1575
5/64
- .078125 - 1.984
37/64 - .578125
- 14.684
5
- .1969
3/32
- .09375
19/32 - .59375
- 15.081
6
- .2362
7/64
- .109375 - 2.778
39/64 - .609375
- 15.478
7
- .2756
1/8
- .125
- 15.875
8
- .3150
9/64
- .140625 - 3.572
41/64 - .640625
- 16.272
9
- .3543
5/32
- .15625
- 0.794
- 1.588
- 2.381
- 3.175
5/8
Decimal
- .5625
- .625
Millimeter
21/32 - .65625
- 16.669
10
- .3937
11/64 - .171875 - 4.366
43/64 - .671875
- 17.066
11
- .4331
3/16
- .4724
- .1875
- 3.969
Fraction
11/16 - .6875
- 17.462
12
13/64 - .203125 - 5.129
45/64 - .703125
- 17.859
13
- .5119
7/32
23/32 - .71875
- 18.256
14
- .5519
15/64 - .234375 - 5.953
47/64 - .734375
- 18.653
15
- .5906
1/4
3/4
- .6300
- .21875
- .25
- 4.762
- 5.556
- 19.050
16
17/64 - .265625 - 6.747
49/64 - .765625
- 19.447
17
- .6693
9/32
25/32 - .78125
- 19.844
18
- .7087
19/64 - .296875 - 7.541
51/64 - .796875
- 20.241
19
- .7480
5/16
- .28125
- .3125
- 6.350
- 7.144
- 7.938
- .75
13/16 - .8125
- 20.638
20
- .7874
21/64 - .328125 - 8.334
53/64 - .828125
- 21.034
21
- .8268
11/32 - .34375
27/32 - .84375
- 21.431
22
- .8661
55/64 - .859375
- 21.828
23
- .9055
- 8.731
23/64 - .359375 - 9.128
3/8
- 22.225
24
- .9449
25/64 - .390625 - 9.921
- .375
- 9.525
57/64 - .890625
- 22.622
25
- .9843
13/32 - .40625
- .875
29/32 - .90625
- 23.019
27/64 - .421875 - 10.716
59/64 - .921875
- 23.416
7/16
- .4375
- 10.319
7/8
15/16 - .9375
- 23.812
29/64 - .453125 - 11.509
61/64 - .953125
- 24.209
15/32 - .46875
31/32 - .96875
- 24.606
31/64 - .484375 - 12.303
63/64 - .984375
- 25.003
1/2
1
- 25.400
- .5
- 11.112
- 11.906
- .12.700
- 1.
To convert millimeters to inches, multiply by .03937
To convert inches to millimeters, multiply by 25.40
-67-
CHAPTER XII
Glossary
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
requirements.
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.
Armature:
• 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.
-68-
Bearings:
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.
-69-
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 motor.
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.
-70-
Foot-Pound: Energy required to raise a one-pound weight against the
force of gravity the distance of one foot. A measure of torque. Inch-pound
is also commonly used on smaller motors and gear reducers. An inchpound represents the energy needed to lift one pound one inch; an inchounce 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
point.
• A malfunction caused by insulation breakdown, allowing current flow to
ground rather than through the intended circuit.
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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
HP
T
N
= T (in.-oz) x 9.917 x N x 107
where,
= horsepower
= Torque
= 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.
-72-
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 singlephase operation: shaded pole, permanent split capacitor (PSC), split
phase, capacitor start/induction run and capacitor start/capacitor run.
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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, flangemounted, 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 non-profit 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 characteristics.
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 shaft.
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 rotation.
Plugging: A method of braking a motor that involves applying partial or
full voltage in reverse to bring the motor to zero speed.
-74-
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).
Power Factor
=
Real Power
Apparent Power
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.
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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 cast-aluminum 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 generalpurpose 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.
-76-
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: The difference between RPM of the rotating magnetic field and RPM
of the rotor in an induction motor. Slip is expressed in percentage and may
be calculated by the following formula:
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.
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.
-77-
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 motors.
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 fullload 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
equipment.
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.
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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.
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