The service factor - SF - is a measure of periodically overload capacity at which a motor can operate without overload or 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:
|Service Factor - SF|
|Synchronous Speed (RPM)|
|1/6, 1/4, 1/3||1.35||1.35||1.35||1.35|
|1 1/2 and up||1.115||1.15||1.15||1.15|
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.