8/4/2019 Motor Terminology
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MOTOR TERMINOLOGY
Ambient (Amb.) The temperature of the space around the
motor.Most motors are designed to operate in an ambient not over
40C(104F).
Note: A rating of 40C Ambient is not the same as a rating of 40C
Rise;see Temperature Rise.
Bearings (Brgs.) Basic types:
Sleeve (Slv.) A bearing that is made of a sleeve bushing. In
frac-tional hp motors, sleeve bearings are used on motors with low
tomoderate radial and axial loads.
Unit Motors are constructed with a long, single sleeve
bearing.For fan duty only. All-position mounting unless otherwise
stated.
Ball Used where higher load capacity is required or ball bearing
is
preference. Common means used to keep out dirt:Shields Metal
rings with close running clearance on one side(single-shielded) or
both sides (double shielded) of bearing.
Seals Similar to shields, except have rubber lips that
pressagainst inner race, more effectively excluding dirt, etc.
Capacitors A device that stores electrical energy. When
connected inan alternating current circuit, the capacitor causes
the current to leadthe voltage in time phase. Two kinds of
capacitors are normally used inAC induction motors. A start
capacitor is connected in series with theauxiliary circuit. It can
only stay energized for a short period of time.Therefore it is only
energized when the motor is started and it isremoved from the
circuit after the motor reaches operating speed.The run capacitor
can stay energized continuously. Therefore, it staysin the circuit
even after the motor reaches operation speed and used inPSC and the
running circuit of capacitor-start capacitor-run motors.
Capacitor value and voltage rating are essential to the proper
motoroperation. Always use the correct capacitor as specified by
the motormanufacturer to insure maximum performance and life and
safe oper-ation of the motor.
Efficiency The ratio of output power divided by input power;
usuallyexpressed as a percentage. A measure of how well the
electrical ener-gy input to a motor is converted into mechanical
energy at the outputshaft. The higher the efficiency, the better
the conversion process andthe lower the operating costs.
Enclosure (Encl.) Defines the motor construction according to
envi-ronmental protection and method of cooling. Types include:
Open A motor that has openings, which permit passage of
exter-nal cooling air over and around the windings. Usually used
indoors,in fairly clean locations.
Open Dripproof (ODP) Ventilation openings are so constructedthat
successful operation is not interfered with when drops of l iquidor
solid particles strike or enter the enclosure at any angle from
0to15 degrees downward from vertical.
Weather-Protected Type I (WPI) Ventilation passages are so
con-structed as to minimize the entrance of rain, snow and
air-borneparticles to the electric parts.
Weather-Protected Type II (WPII) In addition to the
enclosuredefined for a Weather-Protected Type I motor, its
ventilating pas-sages at both intake and discharge are so arranged
that high velocity
air and air-borne particles blown into the motor by storms or
highwinds can be discharged without entering the internal
ventilationpassages leading directly to the electrical parts of the
motor.
Totally Enclosed A motor, which is enclosed to prevent the
freeexchange of air between the inside and outside of the motor,
but notsufficiently enclosed to be termed airtight. Air and dust
does notenter in sufficient quantity to interfere with satisfactory
operation ofthe motor. Used in locations, which are dirty, damp and
oily, etc.
Totally Enclosed Fan Cooled (TEFC) A frame-surface cooled
motorequipped for self exterior cooling by means of a fan or fans
integralwith the motor but external to the enclosing parts.
Totally Enclosed Non-ventilated (TENV) A frame-surface
cooledmotor which is only equipped for cooling by free convection.
Not
equipped with an external cooling fan.Totally Enclosed Air-Over
(TEAO) A frame-surface cooled motorintended for exterior cooling by
a ventilating means external to themotor.
Frame Usually refers to the NEMA system of standardized
motormounting dimensions, which facilitates interchangeability.
Full-Load Amps (FLA) Line current (amperage) drawn by a
motorwhen operating at rated HP and voltage. Shown on motor
nameplate.Important for proper wire size selection, motor starter
heater selec-tion, and over current protection.
Hazardous Location Motor A totally enclosed motor designed
towithstand an internal explosion of specified gases or vapors and
notallow the internal flame or explosion to escape.
Hertz (Hz) Frequency, in cycles per second, of AC power; usually
60Hz in the USA and 50 Hz overseas.
Horsepower See Power.
Insulation (Ins.) In motors, usually classified by maximum
allowableoperating temperatures as defined by U.L.:
Class A - 105C (221F)
Class B - 130C (266F)
Class F - 155C (311F)
Class H - 180C (356F)
Motor Speeds:
Synchronous The theoretical maximum speed at which an
induc-tion-type motor can operate. Synchronous speed is determined
bythe power line frequency and motor design (number of poles)
andcalculated by the formula:
Syn. RPM = Power Supply Hz x 120No. of Poles
Full-Load The nominal speed at which an induction motor
operatesunder rated HP conditions. This will always be less than
the synchro-nous speed and will vary depending on the rating and
characteristicsof the particular motor. For example, four pole 60
Hz fractionalhorsepower motors have a synchronous speed of 1800
RPM, a nomi-nal full load speed (as shown on the nameplate) of 1725
RPM, and anactual full load speed ranging from 1715 to 1745
RPM.
8/4/2019 Motor Terminology
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MOTOR TERMINOLOGY
Motor Types Classified by operating characteristics and/or type
ofpower required:
Single Phase Available in these types:
Shaded Pole Low starting torque. Usually used in
direct-drivefans and blowers.
Permanent Split Capacitor (PSC) Performance and
applicationssimilar to shaded pole but more efficient, with lower
line currentand higher horsepower capabilities.
Split-Phase Start, Induction Run (or simply Split-Phase)
Moderate starting torque, high breakdown torque. Used on
easy-starting equipment such as belt-driven fans and
blowers,grinders, centrifugal pumps, gear motors, etc.
Split-Phase Start, Capacitor Run Same performance as induc-tion
run, except higher efficiency.
Capacitor Start, Induction Run (or Capacitor Start) High
start-ing and breakdown torque, medium starting current. Used
onhard-starting applications: compressors, positive
displacementpumps, farm equipment, etc.
Capacitor Start, Capacitor Run Similar to capacitor start,
induc-tion run, except have higher efficiency. Generally used in
higherHP single-phase ratings.
Three Phase Operate on three-phase power only. High startingand
breakdown torque, high efficiency, medium star ting current,simple,
rugged design, long life. For industrial uses.
Direct Current (DC) Usable only if DC available. Use with
aDC/SCR control enables adjustable-speed applications.
Mounting (Mtg.) Basic types:
Bolted Motor is attached to frame with removable bolts.
Rigid Motor solidly fastened to equipment through metal basethat
is welded, bolted, or cast into the metal shell or clamped to
theend shield hubs.
Cradle/Resilient (Res.) Motor shell isolated from base by
vibration-absorbing material, such as rubber rings on the end
shields, toreduce transmission of vibration to the driven
equipment.
Face or Flange Shaft end has a flat mounting surface, machined
tostandard dimensions, with holes to allow easy, secure mounting
todriven equipment. Commonly used on pumps, oil burners and
gearreducers.
Stud Motor has bolts extending from front or rear, by which it
is
mounted. Often used on small, direct-drive fans and blowers.
Yoke Tabs or ears are welded to motor shell, to allow
boltingmotor to a fan column or bracket.
Power The energy used to do work. Also the rate at which work
isdone. Measured in watts, horsepower, etc.
Power Factor The ratio of real power (watts) divided by
apparentpower (volt-amperes). Do not confuse power factor with
efficiency. Ameasure of the extent to which power transmission or
distribution sys-tems are fully utilized.
Power Supply The voltage of the supply line, which can be
singlephase or three phase.
Rotation (Rot.) Direction in which shaft rotates:
CW = clockwise
CCW = counterclockwise
Rev (CW/CCW) = reversible or bi-directional rotation which can
bechanged.
Service Factor (SF) A measure of the reserve margin built into
amotor. Motors rated over 1.0 SF have more than normal margin,
andare used where unusual conditions such as occasional high or low
volt-age, momentary overloads, etc., are likely to occur.
Severe Duty A totally enclosed motor with extra protection
(for
example: shaft slinger, gasketed terminal box) to resist entry
of con-taminants. Used in extra dir ty, damp or other non-hazardous
contami-nated environments.
Temperature Rise The amount by which a motor, operating
underrated conditions, is hotter than its surroundings. On most
motors,manufacturers have replaced the Rise rating on the motor
nameplatewith a listing of the Ambient temperature rating,
insulation class andservice factor.
Thermal Protector A temperature-sensing device built into
themotor that shuts off the motor if the temperature becomes
excessivedue to failure-to-start or overloading. Especially
important for motorsthat start automatically, are located remotely,
unattended or out-of-sight of operator. Basic t ypes:
Automatic Reset (Auto) After motor cools, thermal protector
automatically restores power. Should not be used where
unexpect-ed restarting would be hazardous.
Manual Reset (Man.) An external button must be pushed torestore
power to motor. Preferred where unexpected restartingwould be
hazardous, as on saws, conveyors, compressors, etc.
Impedance (Imp.) or Impedance Protected Motor is designed sothat
it will not burn out in less than 15 days under locked
rotor(stalled) conditions, in accordance with UL standard No.
519.
Thermostat A temperature sensing device, with external
leads,which must be properly connected to the control circuit of
the motorcontroller to limit the frame or winding temperature of
the motor.
Torque Twist, or turning ability, as applied to a shaft.
Measured infoot-pounds (ft.-lbs.), inch-pounds (in.-lbs.),
ounce-feet (oz.-ft.) orounce-inches (oz.-in.). In motors the torque
values are:
Locked Rotor Torque, or Starting Torque The maximum
torqueproduced at initial start.
Breakdown Torque The maximum torque a motor will producewhile
running, without an abrupt drop in speed and power.
Voltage The pressure in an electrical system. The force pushing
theelectric current through the circuit, like pressure in a water
system.
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