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General Electric Motor Definitions


Voltage:
Common 60hz voltages for single-phase motors are 115 volt, 230 volt, and 115/230 volt.
Common 60hz voltages 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 marking 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.

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 shaded pole type as the latter's will not normally be 50% - 60% higher. Compare PSC with PSC, capacitor start, and so forth.

Hertz Frequency:
In North America 60 hz (cycles) is the common power source. However most of the rest of the world is supplied with 50 hz power.

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:
HP = Torque (lb-ft) x RPM / 5250
HP = Torque (oz-ft) x RPM / 84000
HP = Torque (in-lbs) x RPM / 6300

Torque:
The turning effort or force applied to a shaft, usually expressed in inch-pounds or inch-ounces for fractional or 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 full-load speed at rated horsepower.

Breakdown Torque:
The maximum torque a motor will develop under increasing load conditions without an abrupt drop in speed and power (sometimes called pull-out torque).

Pull-Up Torque:
The minimum torque delivered by a motor between zero and the rated RPM, equal to the maximum load a motor can accelerate to rated RPM.

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:
 
60hz
50hz
Synch.
Speed
2 Pole
3450
2850
3600
4 Pole
1725
1425
1800
6 Pole
1140
950
1200
8 Pole
850
700
900


Synchronous speed (no-load) can be determined by this formula:
Frequency (hertz) x 120 / Number of Poles

Insulation Class:
Insulation systems are rated by standard NEMA classifications according to maximum allowable operating temperatures. They are as follows:
Class Maximum Allowed Temperature (*)

Class Temp.
A 105º C 221º F
B 130º C 266º F
F 155º C 311º F
H 180º C 356º F


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 determining maximum potential loading.

The NEMA standard service factor for totally enclosed motors is 1.0. However, many manufacturers build TEFC motors with 1.15 service factors.

Capacitors:
Capacitors are used on single-phase induction motors except shaded-pole, split-phase and polyphase. Start capacitors are designed to stay in circuit a very short time (3-5 seconds), while run capacitance are permanently in circuit. Capacitors are rated by capacitance and voltage. Never use a capacitor with lower capacitance or voltage ratings for replacement. A higher voltage is acceptable.

Efficiency:
A motor's efficiency is a measurement of useful work produced by the motor versus the energy that 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. 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.

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.

Speed Electric Drives:
Reliable, easy-to-use units are available today for controlling the speed of AC and DC industrial motors. Both types use solid state devices for power control. DC drives are the more straightforward, commonly using silicon controlled rectifiers (SCR's) to convert AC line voltage to controlled DC voltage, which is then applied to the armature of a direct current motor. The more voltage applied to the armature, the faster it will turn. DC drives of this type represent an excellent value for motors up to approximately 3 HP, allowing 60:1 speed regulation and full torque even at reduced speeds. The most common type of AC drive today begins much the same way as a DC drive does - by rectifying "pulsing" AC line voltage to pulse-free DC voltage. However, instead of outputting the DC voltage, the AC drive must re-introduce pulses into the output in order to meet the needs of an AC motor.

This is done using solid-state switches, such as insulated gate bipolar transistors (IGBT's) or gate turn off SCR's (GTO's). The result is a control technique known as pulse width modulation (PWM), perhaps the most highly regarded type of AC drive for many industrial applications. Motor speed varies with the frequency of the pulses introduced into the output voltage.

Pulse width modulated AC drives offer an extremely wide speed range, a host of control functions including programmable acceleration and deceleration ramps and several preset speeds, excellent energy efficiency and, in many cases, speed and torque precision equal to or closely approaching that of a DC system. Perhaps the major reason for their growing popularity, however, is their ability to work with the wide range of AC induction motors available for industry, usually at a price competitive with that of a DC drive package.

NOTE: All above data is for reference purposes only

Understanding NEMA Frames: A Reference Guide


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.

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 holes parallel to the base. It has no significance in a footless motor. Refer to NEMA Standard Dimension Chart.

NEMA Suffixes

C = NEMA C face mounting (specify with or without rigid base)
D = NEMA D flange mounting (specify with or without rigid base)
H = Indicates a frame with rigid base having an F dimension larger than that of the same frame without the suffix H. For example, combination of 56H base motors have mounting holes for NEMA 56 and NEMA 143-5T and a standard NEMA 56 shaft.
J = NEMA C face, threaded shaft pump motor
JM = Close-coupled pump motor with specific dimensions and bearings
JP = Closed-coupled pump motor with specific dimensions and bearings
M = 6 3/4" flange (oil burner)
N = 7 1/4" flange (oil burner)
T, TS = Integral horsepower NEMA standard shaft dimensions if no additional letters follow the "T" or "TS."
TS = Motor with NEMA standard "short shaft" for belt driven loads
Y = Non-NEMA standard mount; a drawing is required to be sure of dimensions. Can indicate a special base, face or flange.
Z = Non-NEMA standard shaft; a drawing is required to be sure of dimensions.

NEMA Prefixes

Letters or numbers appearing in front of the NEMA frame number are those of the manufacturer. They have no NEMA frame significance. 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 motors securely to the mounting base of equipment or to a rigid, flat surface, preferably metallic.

Types of Mounts


Rigid base

Is bolted, welded or cast on main frame and allows motor to be rigidly mounted on equipment.

Resilient base

Has isolation or resilient rings between motor mounting hubs and base to absorb vibration 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 a 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 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

Have bolts protruding from the front or rear of the motor by which the driven load is mounted. This is usually used in applications involving small direct drive fans or blowers.

Types of Enclosures


Drip-proof

Vents in endshield and/or frame are to prevent drops of liquid from falling into motor within a 15 degree angle from vertical. Designed for use in areas that are reasonably dry, clean, and well ventilated (usually indoors). If installed outdoors, it is recommended that the motor be protected with a cover that does not restrict the flow of air to the motor.

Totally enclosed air over (TEAO)

Dust-tight fan and blower duty motors designed for shaft mounted fans or belt driven fans. The motor must be mounted within the airflow of the fan.

Totally enclosed non-ventilated (TENV)

No vent openings, tightly enclosed to prevent the free exchange of air, but not airtight. Has no external cooling fan and relies on convection for cooling. Suitable for use where exposed to dirt or dampness, but not very moist or hazardous (explosive) locations.

Totally enclosed fan cooled (TEFC)

Same as TENV except has external fan as an integral part of the motor, to provide cooling by blowing air around the outside frame of the motor.

Totally enclosed, hostile and severe environment motors

Designed for use in extremely moist or chemical environments, but not for hazardous locations.

Totally enclosed blower cooled motors

Same as TEFC except external fan must run on a power supply that is independent of the inverter output. Cooling per MG 1.6 (IC 46).

Explosion-proof motors

Have bolts protruding from the front or rear of the motor by which the driven load is mounted. This is usually used in applications involving small direct drive fans or blowers.

CLASS I (Gases, Vapors)

Group A Acetylene
Group B Butadiene, ethylene oxide, hydrogen, propylene oxide
Group C Acetaldehyde, cyclopropane, diethel ether, ethylene, isoprene
Group D Acetone, acrylonitrite, 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 +400C or -250C unless the motor nameplate specifically permits another value, and is noted on the nameplate and in the literature. LEESON explosion-proof motors are approved for all classes noted except Class I, Groups A & B.

NOTE: All above data is for reference purposes only