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Service Factor

Service factor - SF - is a measure of periodically overload capacity at which a motor can operate without damaging

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electric motor

The service factor - SF - is a measure of periodically overload capacity at which a motor can operate without damage. The NEMA (National Electrical Manufacturers Association) standard service factor for totally enclosed motors is 1.0.

A motor operating continuously at a service factor greater than 1 will have a reduced life expectancy compared to operating at at its rated nameplate horsepower.

NEMA Service Factor at Synchronous Speed (rpm) for drip proof motors:

Power
(hp)
Service Factor - SF
Synchronous Speed (rpm)
360018001200900
1/6, 1/4, 1/3 1.35 1.35 1.35 1.35
1/2 1.25 1.25 1.25 1.25
3/4 1.25 1.25 1.15 1.15
1 1.25 1.15 1.15 1.15
1 1/2 and up 1.115 1.15 1.15 1.15

Example - Service Factor

A 1 HP motor with a Service Factor - SF = 1.15 can operate at

(1 hp) x 1.15

    = 1.15 hp

without overheating or otherwise damaging the motor if rated voltage and frequency are supplied to the motor.

Insulation life and bearings life are reduced by the service factor load.

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  • en: electrical motor service factor overload load current
  • es: servicio de motor el├ęctrico de corriente de carga factor de sobrecarga
  • de: Elektromotor Betriebsfaktor ├ťberlastlaststrom
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