AC (ALTERNATING CURRENT)
The commonly available electric power supplied, an AC generator and is distributed in single or three-phase forms. AC current changes its direction of flow (cycles).

AC MOTORS
A Motor (see motor definition) operating on AC current that flows in either direction (AC current). There are two general types: Induction, and Synchronous.

ACTIVE IRON
The amount of steel (iron) in the stator and rotor of a motor. Usually the amount of active iron is increased or decreased by lengthening or shortening the rotor and stator (they are generally the same length).

AIR GAP
The space between the rotating (rotor) and stationary (stator) member in an electric motor.

AIR PRESSURE SWITCH
Used on motors with blowers to measure the difference in pressure across the filter so as to detect a clogged filter.

AIR TEMPERATURE SWITCH
A device used in air hooded motors to detect the temperature of the exhausted air. When used in this manner an air temperature switch will detect blockage in the cooling air system or long-term motor overload.

ALTITUDE
The atmospheric altitude (height above sea level) at which the motor will be operating; NEMA standards call for an altitude not exceeding 3,300 ft. (1,000 meters). As the altitude increases above 3,300 ft. and the air density decreases, the air stability to cool the motor decreases - for higher altitudes higher grades of insulation or a motor derating are required. DC motors require special brushes for high altitudes.

AMBIENT TEMPERATURE
The temperature of the surrounding cooling medium, such as gas or liquid, which comes into contact with the heated parts of the motor. The cooling medium is usually the air surrounding the motor. The standard NEMA rating for ambient temperature is not to exceed 40ƒC.

ANTI-FRICTION BEARING
An anti-friction bearing is a bearing utilizing rolling elements between the stationary and rotating assemblies.

ARMATURE
The portion of the magnetic structure of a DC or universal motor which rotates

ARMATURE CURRENT, AMPS
Rated full load armature circuit current.

ARMATURE INDUCTANCE, MH
Armature inductance in milli-henries (saturated).

ARMATURE REACTION
The current that flows in the armature winding of a DC motor tends to produce magnetic flux in addition to that produced by the field current. This effect, which reduces the torque capacity, is called armature reaction and can effect the commutation and the magnitude of the motor's generated voltage.

ARMATURE RESISTANCE, OHMS
Armature resistance is measured in ohms at 25ƒ C. (cold)

AXIAL THRUST
The force or loads that are applied to the motor shaft in a direction parallel to the axis of the shaft. (Such as from a fan or pump).

BACK END OF A MOTOR
The back end of a normal motor is the end which carries the coupling or driving pulley. (NEMA) This is sometimes called the drive end (D.E., pulley end P.E.) etc.

BASE SPEED, RPM
The speed which a DC motor develops at rated armature and field voltage with rated load applied.

BEARINGS
Are used to reduce friction and wear while supporting rotating elements. For a motor it must provide a relatively rigid support for the output shaft.
The bearing acts as the connection point between the rotating and stationary elements of a motor. There are various types such as roller, ball, sleeve (journal), and needle.
The ball bearing is used in virtually all types and sizes of electric motors. It exhibits low friction loss, is suited for high speed operation and is compatible in a wide range of temperatures. There are various types of ball bearings such as open, single shielded or sealed. Reliance Electric offers a unique PLS bearing system.

BEARING LIFE
Rating life, L₁₀ (B_l0), is the life in hours or revolutions in which 90% of the bearings selected will obtain or exceed. Median life (average life), L₅₀(B₅₀)
 
BRAKES
An external device or accessory that brings a running motor to a standstill and/or holds a load. Can be added to a motor or incorporated.

BRAKING TORQUE
The torque required to bring a motor down to a standstill. The term is also used to describe the torque developed by a motor during dynamic braking conditions.
 
BREAKDOWN TORQUE
The maximum torque a motor will develop at rated voltage without a relatively abrupt drop or loss in speed.

BRUSH
A piece of current conducting material (usually carbon or graphite) which rides directly on the commutator of a commutated motor and conducts current from the power supply to the armature windings.

CAPACITOR
A device which, when connected in an alternating-current circuit, causes the current to lead the voltage in time phase. The peak of the current wave is reached ahead of the peak of the voltage wave. This is the result of the successive storage and discharge of electric energy used in 1 phase motors to start or in 3 phase for power factor correction.

CAPACITOR MOTOR
A single-phase induction motor with a main winding arranged for direct connection to the power source, and auxiliary winding connected in series with a capacitor. There are three types of capacitor motors: capacitor start, in which the capacitor phase is in the circuit only during starting, permanent-split capacitor, which has the same capacitor and capacitor phase in the circuit for both starting and running; two-value capacitor motor, in which there are different values of capacitance for starting and running.

CAPACITOR START
The capacitor start single phase motor is basically the same as the split phase start, except that it has a capacitor in series with the starting winding. The addition of the capacitor provides a more ideal phase relation and results in greater starting torque with much less power input. As in the case of the split phase motor, this type can be reversed at rest, but not while running unless special starting and reversing switches are used. When properly equipped for reversing while running, the motor is much more suitable for this service than the split phase start as it provides greater reversing ability at less watts input.

CENTRIFUGAL CUTOUT SWITCH
A centrifugally operated automatic mechanism used in conjunction with split phase and other types of single phase induction motors. Centrifugal cutout switches will open or disconnect the starting winding when the rotor has reached a pre-determined speed, and reconnect it when the motor speed falls below it. Without such a device, the starting winding would be susceptible to rapid overheating and subsequent burnout.

CLUTCH
A mechanical device for engaging and disengaging a motor often used when many starts and stops are required.

CONDUCTOR
A material, such as copper or aluminum, which offers low resistance or opposition to the flow of electric current.

CONDUIT BOX
The metal container usually on the side of the motor where the stator (winding) leads are attached to leads going to the power supply.

COGGING
A term used to describe non-uniform angular velocity. It refers to rotation occurring in jerks or increments rather than smooth motion. When an armature coil enters the magnetic field produced by the field coils, it tends to speed up and slow down when leaving it. This effect becomes apparent at low speeds. The fewer the number of coils, the more noticeable it can be.
 
COIL (Stator or Armature)
The electrical conductors wound into the core slot, electrically insulated from the iron core. These coils are connected into circuits or windings which carry independent current. It is these coils that carry and produce the magnetic field when the current passes through them. There are two major types: "Mush" or "random" wound, round wire found in smaller and medium motors where coils are randomly laid in slot of stator core; and formed coils of square wire individually laid in, one on top of the other, to give an evenly stacked layered appearance.

COMMUTATOR
A cylindrical device mounted on the armature shaft and consisting of a number of wedge-shaped copper segments arranged around the shaft (insulated from it and each other. The motor brushes ride on the periphery of the commutator and electrically connect and switch the armature coils to the power source.

COMPOUND WOUND DC MOTORS
Designed with both a series and shunt field winding, the compound motor is used where the primary load requirement is heavy starting torque, and adjustable speed is not required. (See Paralleling) Also used for parallel operation. The load must tolerate a speed variation from full-load to no-load.
Industrial machine applications include large planers, boring mills, punch presses, elevators, and small hoists.

CONSTANT H.P.
A designation for variable or adjustable speed motors used for loads requiring the same amount of H.P. regardless of their motor speed during normal operation.

CONSTANT TORQUE
Refers to loads whose H.P. requirements change linearly with changing speeds. Horsepower varies with the speed, i.e.- 2/1 HP at 1800/900 RPM. (Seen on some 2-speed motors). Possible applications include conveyors, some crushers, or constant-displacement pumps.

CONSTANT SPEED
A DC motor which changes speed only slightly from a no load to a full load condition. In AC motors, these are synchronous motors.

CORE
The iron portion of the stator and rotor; made up of cylindrical laminated electric steel. The stator and rotor cores are concentric separated by an air gap, with the rotor core being the smaller of the two and inside to the stator core.

COUNTER ELECTROMOTIVE FORCE (CEMF)
The induced voltage in a motor armature, caused by conductors moving through or "cutting" field magnetic flux. This induced voltage opposes the armature current and tends to reduce it.

COUPLINGS
The mechanical connector joining the motor shaft to the equipment to be driven.

CURRENT
The time rate of flow of electrical charge and is measured in amps (amperes).

CYCLES PER SECOND (HERTZ)
One complete reverse of flow of alternating current per rate of time. (A measure of frequency.) 60 HZ (cycles per second) A.C. power is common throughout the U.S. and 50 HZ is more common in some foreign countries.
 
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