AC motorA motor powered by alternating current.
Air gapThe space between stator and rotor magnetic surfaces.
Ambient temperatureThe surrounding air temperature near the motor.
Angular speedRotational speed expressed in radians per second.
Apparent powerVoltage-current product measured in volt-amperes.
ArmatureA winding or rotating component where voltage is induced.
Back EMFVoltage generated by rotation that opposes applied voltage.
BearingA component supporting the shaft and reducing friction.
Breakdown torqueMaximum torque before an induction motor stalls.
BrushA sliding electrical contact used in some motor designs.
Brushless DC motorAn electronically commutated permanent-magnet motor.
Capacitor-start motorA single-phase motor using a starting capacitor.
Continuous dutyOperation long enough to reach thermal equilibrium.
Copper lossResistive winding loss proportional to current squared.
Core lossMagnetic loss from hysteresis and eddy currents.
CurrentElectric charge flow measured in amperes.
DC motorA motor powered from direct current.
Delta connectionThree windings connected end-to-end in a triangle.
DemandElectrical power required at a particular time.
Duty cycleThe pattern of operating and resting periods.
EfficiencyMechanical output divided by electrical input.
Electrical horsepowerA power unit equal to 746 watts by convention.
EnergyPower accumulated over time, commonly measured in kWh.
EnclosureMotor housing style protecting internal components.
Frame sizeStandardized motor mounting and shaft dimensions.
FrequencyAlternating-current cycles per second, measured in hertz.
Full-load ampsCurrent drawn near rated load and rated voltage.
Full-load torqueTorque produced at rated power and speed.
HorsepowerA mechanical power unit equal to about 745.7 watts.
Hysteresis lossCore energy lost during magnetic field reversal.
Induction motorAn AC motor with rotor current induced magnetically.
Insulation classThermal capability category for winding insulation.
Intermittent dutyOperation involving repeated load and rest intervals.
Inverter dutyMotor suitability for variable-frequency drive operation.
KilowattOne thousand watts of power.
Kilowatt-hourEnergy used by one kilowatt during one hour.
Line currentCurrent flowing in a supply conductor.
Line voltageVoltage measured between supply lines.
Load factorAverage load divided by peak or rated load.
Locked-rotor currentCurrent drawn when the rotor cannot turn.
Locked-rotor torqueTorque developed when the rotor is stationary.
Mechanical horsepowerExactly 550 foot-pounds per second.
Metric horsepowerA power unit equal to 735.49875 watts.
Motor slipDifference between synchronous and rotor speed.
NameplateManufacturer label listing rated motor information.
NEMA designMotor torque and starting characteristic classification.
Newton-meterSI unit of torque.
Output powerUseful mechanical power delivered at the shaft.
OverloadOperation above a motor's allowable thermal loading.
Phase currentCurrent within an individual three-phase winding.
Phase voltageVoltage across an individual motor phase winding.
PowerRate of energy transfer or work.
Power factorReal power divided by apparent power.
Premium efficiencyA high-efficiency motor classification.
Reactive powerNon-working AC power measured in VAR.
Real powerAverage useful electrical power measured in watts.
RotorThe rotating magnetic or current-carrying motor element.
Service factorAllowed loading multiplier under stated conditions.
Shaft powerMechanical power available at the motor shaft.
Single-phaseAn AC supply with one alternating voltage system.
Slip frequencyRotor electrical frequency related to induction slip.
Soft starterA controller reducing starting voltage and current.
SpeedRate of shaft rotation.
Stall torqueTorque available at zero shaft speed.
Starting currentCurrent drawn while accelerating from rest.
StatorThe stationary magnetic structure and winding.
Synchronous speedMagnetic field speed set by frequency and pole count.
Temperature riseMotor temperature above ambient during operation.
Three-phaseAn AC system using three phase-shifted voltages.
TorqueRotational force applied about a shaft.
Torque constantTorque produced per ampere in a motor.
Variable-frequency driveA controller adjusting motor frequency and voltage.
VoltUnit of electrical potential difference.
Volt-ampereUnit of apparent AC power.
Voltage balanceSimilarity of three phase-to-phase voltages.
WattSI unit of power equal to one joule per second.
WindingInsulated conductors creating a motor magnetic field.
Wye connectionThree windings joined at a common neutral point.
Windage lossMechanical loss from moving air or gas.
WorkForce acting through a distance.
RPMRevolutions completed during one minute.
RPSRevolutions completed during one second.
Rad/sAngular velocity measured in radians per second.
Power densityPower relative to motor mass or volume.
Thermal limitMaximum allowable motor temperature condition.
Insulation resistanceResistance between windings and grounded motor parts.
Voltage unbalanceUnequal line voltages in a three-phase system.
Current unbalanceUnequal phase currents under operating load.
No-load currentCurrent used while the shaft delivers minimal load.
No-load lossMotor losses measured without significant shaft output.
Peak torqueHighest short-duration torque available.
Rated torqueTorque corresponding to rated power and rated speed.
Rated currentCurrent specified for rated operating conditions.
Rated voltageSupply voltage specified for normal operation.
Rated frequencySupply frequency specified for normal operation.
Pole countNumber of magnetic poles determining synchronous speed.
Thermal protectorDevice responding to excessive motor temperature.
Overload relayDevice protecting a motor from sustained overcurrent.
ContactorElectrically controlled switch used for motor power.
DisconnectMeans of isolating motor electrical power.
Shaft keyMechanical feature transmitting torque to attached equipment.
CouplingComponent connecting the motor shaft to a load.
GearmotorA motor integrated with a speed-reduction gearbox.
RegenerationReturning mechanical energy to the electrical system.
Braking torqueTorque that opposes shaft rotation.
Dynamic brakingElectrical method converting motion energy into heat.
Regenerative brakingBraking that returns energy to the supply.
CommutationSwitching current among motor windings.
EncoderSensor reporting speed, direction, or shaft position.
ResolverRotary transformer sensor for angular position.
Hall sensorMagnetic sensor often used for rotor position.
Cogging torqueTorque ripple caused by magnetic position preference.
Torque ripplePeriodic variation in developed torque.
HarmonicFrequency component at a multiple of the fundamental.
Total harmonic distortionCombined harmonic content relative to the fundamental.
Crest factorPeak waveform value divided by RMS value.
RMS currentEffective current value producing equivalent heating.
RMS voltageEffective voltage value producing equivalent heating.
Apparent efficiencyA simplified efficiency inferred from available measurements.
Load profilePower or torque demand changing over time.
Base speedSpeed below which a drive maintains rated torque.
Field weakeningOperation above base speed using reduced magnetic flux.
Constant torque loadA load requiring nearly constant torque across speed.
Variable torque loadA load whose torque often changes with speed squared.
Constant power loadA load requiring similar power across a speed range.
Affinity lawsRelationships for fan or pump flow, pressure, and power.
Pump curveGraph relating pump head, flow, and efficiency.
Fan curveGraph relating airflow, pressure, and power.
Compressor loadMechanical demand created by gas compression.
InertiaResistance of rotating mass to speed change.
Acceleration timeTime needed to reach operating speed.
Deceleration timeTime needed to slow from operating speed.
Duty pointOperating condition where equipment and system curves meet.
Shaft alignmentCollinearity of coupled rotating shafts.
MisalignmentOffset or angle error between coupled shafts.
VibrationOscillating mechanical motion used in condition monitoring.
Bearing currentUnwanted electrical current passing through bearings.
GroundingConnection intended to control fault and common-mode voltage.
ShieldingConductive protection reducing electromagnetic interference.
Common-mode voltageVoltage shared by conductors relative to ground.
Carrier frequencyDrive switching frequency used to synthesize output.
Switching lossPower lost during semiconductor switching.
Motor deratingReducing allowable output for adverse conditions.
Altitude deratingOutput reduction due to lower air density at altitude.
Ambient deratingOutput reduction due to elevated surroundings.
Enclosure ratingProtection level against solids, water, and environment.
Ingress protectionIP code describing enclosure resistance to intrusion.
Totally enclosed fan cooledMotor enclosure cooled by an external fan.
Open drip proofVentilated motor design limiting falling liquid entry.
Explosion-proofEnclosure designed for specified hazardous locations.
Hazardous locationArea containing potentially ignitable substances.
S1 dutyIEC continuous running duty classification.
S2 dutyIEC short-time duty classification.
S3 dutyIEC intermittent periodic duty classification.
S4 dutyIEC intermittent duty including starting.
S5 dutyIEC intermittent duty including electric braking.
S6 dutyIEC continuous operation with periodic load changes.
S7 dutyIEC continuous duty with starting and braking.
S8 dutyIEC continuous duty with periodic speed changes.
S9 dutyIEC duty with non-periodic load and speed changes.
S10 dutyIEC duty with discrete constant loads and speeds.