Glossary / Technology

Motors Glossary

AC Motors: A Motor (see motor definition) operating on AC current that flows in either direction (AC current).
Active Iron: The amount of steel (iron) in the stator and rotor of a motor. Usually the amount of active iron is
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
Air Temperature Switch: A device used in air hooded motors to detect the temperature of the exhausted air. When used in this
Alternating Current (AC): The commonly available electric power supplied, an AC generator and is distributed in single or thre
Altitude: The atmospheric altitude (height above sea level) at which the motor will be operating: NEMA standar
Ambient Temperature: The temperature of the surrounding cooling medium, such as gas or liquid, which comes into contact w
Anti-Friction Bearing: An anti-friction bearing is a bearing utilizing rolling elements between the stationary and rotating
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 addit
Armature Resistance (Ohms): Armature resistance is measured in ohms at 25f C. (cold)
Axial Thrust: The force or loads that are applied to the motor shaft in a direction parallel to the axis of the sh
Back End Of A Motor: The back end of a normal motor is the end which carries the coupling or driving pulley. (NEMA) This
Base Speed (RPM): The speed which a DC motor develops at rated armature and field voltage with rated load applied.
Bearing Life: Rating life, L10 (Bl0), is the life in hours or revolutions in which 90% of the bearings selected wi
Bearing Rtd: A probe used to measure bearing temperature to detect an overheating condition. The RTD's resistance
Bearings: Are used to reduce friction and wear while supporting rotating elements. For a motor it must provide
Brakes: An external device or accessory that brings a running motor to a standstill and/or holds a load. Can
Braking Torque: The torque required to bring a motor down to a standstill. The term is also used to describe the tor
Breakdown Torque: The maximum torque a motor will develop at rated voltage without a relatively abrupt drop or loss in
Brush: A piece of current conducting material (usually carbon or graphite) which rides directly on the comm
C Flange: A type of flange used with close coupled pumps, speed reducers, and similar applications where the m
Canopy (Dripcover): A protective cover placed on the top of a motor being mounted vertically to protect it from liquids
Capacitor: A device which, when connected in an alternating-current circuit, causes the current to lead the vol
Capacitor Motor: A single-phase induction motor with a main winding arranged for direct connection to the power sourc
Capacitor Start: The capacitor start single phase motor is basically the same as the split phase start, except that i
Centrifugal Cutout Switch: A centrifugally operated automatic mechanism used in conjunction with split phase and other types of
Clutch: A mechanical device for engaging and disengaging a motor often used when many starts and stops are r
Cogging: A term used to describe non-uniform angular velocity. It refers to rotation occurring in jerks or in
Coil (Stator Or Armature): The electrical conductors wound into the core slot, electrically insulated from the iron core. These
Commutator: A cylindrical device mounted on the armature shaft and consisting of a number of wedge-shaped copper
Complete: A complete test is a test which meets the requirements of IEEE-112-1978. It includes the tests condu
Compound Wound DC Motors: Designed with both a series and shunt field winding, the compound motor is used where the primary lo
Conductor: A material, such as copper or aluminum, which offers low resistance or opposition to the flow of ele
Conduit Box: The metal container usually on the side of the motor where the stator (winding) leads are attached t
Constant HP: A designation for variable or adjustable speed motors used for loads requiring the same amount of H.
Constant Speed: A DC motor which changes speed only slightly from a no load to a full load condition. In AC motors,
Constant Torque: Refers to loads whose H.P. requirements change linearly with changing speeds. Horsepower varies with
Core: The iron portion of the stator and rotor: made up of cylindrical laminated electric steel. The stato
Counter Electromotive Force (CEMF): The induced voltage in a motor armature, caused by conductors moving through or 'cutting' field magn
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 H
D Flange: A special end shield with holes for through bolts in the flange and is primarily used for mounting t
Dc Motor: A motor using either generated or rectified D.C. power (see Motor definition) . A DC motor is usuall
Definite Purpose Motor: A definite purpose motor is any motor design, listed and offered in standard ratings with standard o
Design A B C D: NEMA has standard NEMA motor designs of various torque characteristics to meet the various requireme
Dimensions: NEMA has standard frame sizes and dimensions designating the height of the shaft, the distance betwe
Direct Current (DC): A current that flows only in one direction in an electric circuit. It may be continuous or discontin
Drip-Proof Guarded: A drip-proof machine with ventilating openings guarded (with screens) as in a guarded motor.
Drip-Proof Motor: An open motor in which the ventilating openings are so constructed that drops of liquid or solid par
Dual Torque: Dual speed motor whose torque varies with speed (as the speed changes the horsepower remains constan
Dual Voltage: Some motors can operate on two different voltages, depending upon how it is built and connected. The
Duty Cycle: The relationship between the operating and rest times or repeatable operation at different loads. A
Dynamometer: A device which loads the motor to measure output torque and speed accurately by providing a calibrat
Eddy Current: Localized currents induced in an iron core by alternating magnetic flux. These currents translate in
Efficiency: The efficiency of a motor is the ratio of mechanical output to electrical input. It represents the e
Electrical Degree: A unit of measurement of time as applied to alternating current. One complete cycle =360 electrical
Electrical Unbalance: In a 3 phase supply, where the voltages of the three different phases are not exactly the same. Meas
Electromotive Force (EMF): A synonym for voltage, usually restricted to generated voltage.
Encapsulated Winding: A motor which has its winding structure completely coated with an insulating resin (such as epoxy).
Enclosures: The housing, frame, of the motor of which there are two broad classifications: open and totally clos
Endshield: The part of the motor housing which supports the bearing and acts as a protective guard to the elect
Explosion-Proof Enclosure: A totally enclosed enclosure which is constructed to withstand an explosion of a specified gas, vapo
Explosion-Proof-Hazardous Locations Division 11: Locations in which ignitable concentrations of flammable or combustible material exist but are conta
Explosion-Proof-Hazardous Locations Division I: Location in which ignitable concentrations of flammable or combustible material exist and come in co
Explosion-Proof-UL Classifications Class I: Those in which flammable gasses or vapors are or may be present in the air in quantities sufficient
Externally Ventilated: A motor using an external cooling system. This is required in applications where the motor's own fan
Field: A term commonly used to describe the stationary (Stator) member of a DC Motor. The field provides th
Field Weakening: The introduction of resistance in series with the shunt wound field of a DC motor to reduce the volt
Flange: Mounting endshield with special rabbets and bolt holes for mounting such equipment as pumps and gear
Flux: The magnetic field which is established around an energized conductor or permanent magnet. The field
Form Factor: A figure of merit which indicates how much rectified current departs from pure (non-pulsating) DC. A
Form Wound: A type of coil in which each winding is individually formed and placed into the stator slot. A cross
Fractional-Horsepower Motor: A motor usually built in a frame smaller than that having a continuous rating of one horsepower, ope
Frame: The supporting structure for the stator parts of an AC motor: in a DC motor the frame usually forms
Frame Size: Refers to a set of physical dimensions of motors as established by NEMA. These dimensions include cr
Frequency: The rate at which alternating current makes a complete cycle of reversals. It is expressed in cycles
Front End Of A Motor: The front end of a normal motor is the end opposite the coupling or driving pulley. (NEMA) This is s
Full-Load Current: The current flowing through the line when the motor is operating at full-load torque and full-load s
Full-Load Torque: That torque of a motor necessary to produce its rated horsepower at full-load speed, sometimes refer
Gearhead: The portion of a gearmotor which contains the actual gearing which converts the basic motor speed to
Gearmotor: A gearhead and motor combination to reduce the speed of the motor to obtain the desired RPM's.
General Purpose Motor: A general-purpose motor is any motor having a 'B' design, listed and offered in standard ratings wit
Grounded Motor: A motor with an electrical connection between the motor frame and ground.
Guarded Motor: An open motor in which all openings giving direct access to live or rotating parts (except smooth sh
Heat Exchanger: A device which will transfer the heat from inside the motor to another medium, through a radiator ty
Hertz (Hz): One cycle per second (as in 60 Hz. which is 60 cycles per second).
Horsepower: The measure of rate of work. One horsepower is equivalent to lifting 33,000 pounds to a height of on
Hysteresis Loss: The resistance offered by materials to becoming magnetized (magnetic orientation of molecular struct
I2r: Losses due to current flowing in a conductor caused by resistance (equals the current squared times
Identification: In most instances, the following information will help identify a motor: 1. Frame designation (actua
Inductance: The characteristic of an electric circuit by which varying current in it produces a varying magnetic
Induction Motor: An induction motor is an alternating current motor in which the primary winding on one member (usual
Inertial Load: A load (flywheel, fan, etc.) which tends to cause the motor shaft to continue to rotate after the po
Insulation Class: Since there are various ambient temperature conditions a motor might see and different temperature r
Insulation Systems: Five specialized elements are used, which together constitute the motor's INSULATION SYSTEM. The fol
Insulator: A material which tends to resist the flow of electric current (paper, glass, etc.) In a motor the in
Intermittent Duty: A requirement of service that demands operation for alternate intervals of (1 ) load and no load: or
Interpoles: An auxiliary set of field poles carrying armature current to reduce the field flux caused by armatur
Inverter: An electronic device that converts fixed frequency and fixed voltages to variable frequency and volt
J Seconds (Dc Motors): J is the per unit moment of inertia. It is defined as the time in seconds to accelerate the motor ar
Jackscrew: A device used for leveling the positioning of a motor. These devices are adjustable screws fitting o
Kilowatt: Since the watt is a relatively small unit of power, the kilowatt (kw), 1,000 watts, is used where la
Laminations: The steel portion of the rotor and stator cores made up of a series of thin laminations (sheets) whi
Large Motors: Usually refers to AC motors in 5,000 series frames and above and to 500 series frames and larger in
Load: The burden imposed on a motor by the driven machine. It is often stated as the torque required to ov
Locked Rotor Current: Steady state current taken from the line with the rotor at standstill (at rated voltage and frequenc
Locked Rotor Torque: The minimum torque that a motor will develop at rest for all angular positions of the rotor (with ra
Losses: A motor converts electrical energy into a mechanical energy and in so doing, encounters losses. Thes
Lubrication: In order to reduce wear and avoid overheating certain motor components require lubricating (applicat
Magnetic Polarity: It is a fundamental principle of a winding that adjacent poles must be wound to give opposite magnet
Medium Motors: Motors in NEMA 143T to 449T frames.
Meggar Test: A measure of an insulation system's resistance. This is usually measured in megohms and tested by pa
Motor: A device that takes electrical energy and converts it into mechanical energy to turn a shaft.
Multi-Speed Motors: A motor wound in such a way that varying connections at the starter can change the speed to a predet
Nameplate: The plate on the outside of the motor describing the motor, HP, voltage, RPM's, efficiency, design,
Navy Service (A): Motors designed to meet requirements of MIL M-17059 or MlL M-17060 for high shock and service and ar
NEC Temperature Code (T Code): An index for describing maximum allowable 'skin' (surface) temperature of a motor under any normal o
Noise: A test performed to verify the motor sound level, conducted in accordance with IEEE-85. The tests ar
Oil Mist Lubrication-Dry Sump: A method for lubricating anti-friction bearings which utilizes oil dispersed on an air stream. The m
Oil Mist Lubrication-Wet Sump: Similar to Oil Mist Lubrication - Dry Sump, except that a pool of oil is developed in the bearing ch
Open (Protected) Motor: A motor having ventilating openings which permit passage of external cooling air over and around the
Open Bearing: A ball bearing that does not have a shield, seal or guard on either of the two sides of the bearing
Open Externally-Ventilated Machine: A machine which is ventilated with external air by means of a separate motor-driven blower mounted o
Open Pipe-Ventilated Machine: An open machine except that openings for admission of ventilating air are so arranged that inlet duc
P Base: A special mounting similar to 'D' flange except with a machine fit tenon recessed instead of protrud
Paralleling: When two or more DC motors are required to operate in parallel - that is, to drive a common load whi
Part Winding Start Motor: Is arranged for starting by first energizing part of the primary winding and subsequently energizing
Permanent Magnet Synchronous (PMR): (HYSTERESIS SYNCHRONOUS) A motor with magnets embedded into the rotor assembly, which enable the rot
Phase: Indicates the space relationships of windings and changing values of the recurring cycles of A.C. vo
Pls: An exclusive Reliance bearing and lubricating system which permits complete lubrication of the beari
Plug Reversal: Reconnecting a motor's winding in reverse to apply a reverse braking torque to its normal direction
Polarization Test: A ratio of a one-minute meggar test (see Meggar Test) to ten-minute meggar test. Used to detect cont
Poles: In an AC motor, refers to the number of magnetic poles in the stator winding. The number of poles is
Polyphase Motor: Two or three-phase induction motors have their windings, one for each phase, evenly divided by the s
Power Code: Identifies the type of power supply providing power to a DC motor. Frequency, voltage, and type of r
Power Factor: A measurement of the time phase difference between the voltage and current in an AC circuit. It is r
Primary Winding: That winding of a motor, transformer or other electrical device which is connected to the power sour
Protective Relay: A relay, the principal function of which is to protect service from interruption, or to prevent or l
Pull-In Torque: The maximum constant torque which a synchronous motor will accelerate into synchronism at rated volt
Pull-Up Torque: The minimum torque developed by an AC motor during the period of acceleration from zero to the speed
Random Wound: The standard type of stator winding used in motors under 1,000 volts. The coils are random wound wit
Reactance (Inductive): The characteristic of a coil, when connected to alternating current, which causes the current to lag
Relay: A device that is operative by a variation in the conditions of one electric circuit to effect the op
Reluctance: The characteristic of a magnetic material which resists the flow of magnetic lines of force through
Reluctance Synchronous Motor: A synchronous motor with a special rotor design which directly lines the rotor up with the rotating
Resilient Mounting: A suspension system or cushioned mounting designed to reduce the transmission of normal motor noise
Resistance: The degree of obstacle presented by a material to the flow of electric current is known as resistanc
Reversing: Unless otherwise specified, a general-purpose DC motor is reversible. A DC motor can be reversed by
Revolutions Per Minute (RPM): The number of times per minute the shaft of the motor (machine) rotates. This is a function of desig
Roller Bearing: A special bearing system with cylindrical rollers capable of handling belted applications, too large
Rotating Magnetic Field: The force created by the stator once power is applied to it that causes the rotor to turn.
Rotor: The rotating member of an induction motor made up of stacked laminations. A shaft running through th
Routine: A routine test is a basic test done in the factory to the requirements of NEMA MG1, paragraph 12.51
Screens: Are protection which can be placed over openings in the fan cover on a fan-cooled motor or ventilati
Secondary Winding: Winding which is not connected to the power source, but which carries current induced in it through
Series Dc Motors: Where high starting torques are required for a DC motor, the series motor is used. The load must be
Service Factor: 1. When used on a motor nameplate, a number which indicates how much above the nameplate rating a mo
Shaft: The rotating member of the motor which protrudes past the bearings for attachment to the driven appa
Short-Circuit: A defect in a winding which causes part of the normal electrical circuit to be bypassed. This freque
Shunt Wound Dc Motors: Integral-horsepower shunt motors, are used where the primary load requirements are for minimum speed
Skew: Arrangement of laminations on a rotor or armature to provide a slight angular pattern of their slots
Sleeve Bearings: A type of bearing with no rolling elements, where the motor shaft rides on a film of oil.
Slip: The difference between the speed of the rotating magnetic field (which is always synchronous) and th
Space Heater: Small resistance heater units mounted in a motor, that are energized, during motor shutdown, to prev
Special Purpose Motor: Motor with special operating characteristics or special mechanical construction, or both, designed f
Speed: The speed of the motor refers to the RPM's (revolutions per minute) of the shaft. For a three phase
Splash-Proof Motor: An open motor in which the ventilating openings are so constructed that drops of liquid or solid par
Split Phase Start: Motor which employs a main winding and an auxiliary winding, which is called the starting winding. T
Stabilized Shunt-Wound Motor: A stabilized shunt-wound motor is a direct-current motor in which the shunt field circuit is connect
Starting Current: Amount of current drawn at the instant a motor is energized - in most cases much higher than that re
Starting Torque: The torque or twisting force delivered by a motor at the instant it is energized. Starting torque is
Stator: That part of an AC induction motor's magnetic structure which does not rotate. It usually contains t
Stress Cones: A physical protection placed over the external connections point on medium and high voltage motor le
Suffixes To Nema Frames: Letter suffixes sometimes follow the NEMA frame size. Some of these suffixes, according to NEMA stan
Surge Protection: A capacitor device usually mounted in the conduit box to flatten the voltage surges that may occur a
Synchronous Motor: A motor which operates at a constant speed up to full load. The rotor speed is equal to the speed of
Synchronous Speed: The speed of the rotating magnetic field set up by the stator winding of an induction motor. In a sy
T Frame: Current NEMA designation identifying AC induction motor frames. (NEMA has dimension tables which off
Tachometer: A small generator normally used as a rotational speed sensing device. Tachometers are typically atta
Temperature: Has direct bearing on the life of a given motor and when considering life expectancy, the following
Temperature Rise: Some of the electrical energy losses inherent in motors are converted to heat causing some of the mo
Temperature Tests: Tests conducted to determine the temperature rise of certain parts of a motor above the ambient temp
Tests: A variety of tests are conducted to ensure motor performance, efficiency, and manufacturing integrit
Thermal Protector (Inherent): An inherent overheating protective device which is responsive to motor temperature and which, when p
Thermistor-Thermally Sensitive Resistor: A semiconductor used to measure temperature: can be attached to an alarm or meter to detect motor ov
Thermocouple-Thermal Detection Device: A temperature detecting device made of two dissimilar metals which generate a voltage as a function
Thermostat: Units applied directly to the motor's windings which senses winding temperature and may automaticall
Thrust Bearings: Special bearings used to handle higher than normal axial forces exerted on the shaft of the motor as
Torque: Turning force delivered by a motor or gearmotor shaft, usually expressed in lbs. ft derived by compl
Totally -Enclosed Air-To-Air-Cooled Machine: A totally enclosed machine cooled by circulating internal air through a heat exchanger which, in tur
Totally -Enclosed Enclosure: A motor enclosure which prevents free exchange of air between the inside and the outside of the encl
Totally -Enclosed Fan-Cooled Enclosure: Provides for exterior cooling by means of a fan(s) integral with the machine, but external to the en
Totally- Enclosed Non-Ventilated Enclosure: Has no provisions for external cooling to the enclosing parts. The motor is cooled by heat radiation
Totally-Enclosed Pipe Ventilated Machine: A totally-enclosed machine except for openings so arranged that inlet and outlet ducts or pipes may
Totally-Enclosed Water Air-Cooled Machine: A totally-enclosed machine cooled by circulating air which, in turn, is cooled by circulating water.
Transformer: A device which converts electrical power (alternating current) to electrical power of a different vo
Tube Cooled: A motor in which heat is dissipated by air-to-air heat exchange.
U Frame: A previously used NEMA designation indicating frame size and dimension (prior to 1965 the standard f
Underwriters Laboratory (UL): An independent testing organization which examines and tests devices, systems and materials with par
Vacuum Degassed Bearings: Vacuum degassing is a process used in the purifying of steel for ball bearings assuring a very dense
Variable Torque: A multi-speed motor used on loads whose torque requirements vary with speed as in some centrifugal p
Vertical Motor: A motor being mounted vertically (shaft up or down) as in many pump applications.
Vertical P Base Motor: A vertical motor with a special mounting face conforming to NEMA's 'P' design and with a ring groove
Voltage: The force that causes a current to flow in an electrical circuit. Analogous to pressure in hydraulic
Voltage Drop: Loss encountered across a circuit impedance from power source to applicable point (motor) caused by
Watt: The amount of power required to maintain a current of one ampere at a pressure of one volt. Most mot
Weather-Protected Machine: Type I (WPI) weather-protected machine is an open machine with its ventilating passages so construct
Weather-Protected Machine: Type II (WPII) shall have, in addition to the enclosure defined for a Type 1 weather-protected machi
Winding Rtd: A resistance device used to measure temperature change in the motor windings to detect a possible ov
Witness: A witness test is a test performed with a customer representative present.
Wk2 (Moment Of Inertia): The moment of inertia is expressed as Wk2or WR2in terms of pound-feet squared. It is the product of
Wound Rotor Induction Motor: A wound rotor induction motor is an induction motor in which the secondary circuit consists of polyp
Wye-Delta Starting: A method of starting a motor at rated voltage but drawing locked rotor current and producing reduced

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