Electrical Motors - Service Factors
Calculate design power based on motor power and service factor. Service factor (SF) is a measure of periodic overload capacity at which a motor can operate without being damaged.
Service Factor Calculator
Service factor (SF) is a measure of periodically overload capacity at which a motor can operate without being damaged.
Formula:
PD = SF × P
Where:
- PD = Design Power (hp or W)
- SF = Service Factor
- P = Motor Power (hp or W)
A motor operating continuously at a service factor greater than 1 will have a reduced life expectancy compared to operating at its rated nameplate horsepower.
NEMA Service Factor Reference
The table above shows NEMA service factors for drip-proof motors at various synchronous speeds and power ratings.
Example: A 1 HP motor with a Service Factor of 1.15 can operate at:
PD = 1 hp × 1.15 = 1.15 hp
without overheating or damaging the motor (assuming rated voltage and frequency are supplied).
Note: Insulation life and bearing life are reduced by operating at service factor loads.