Number by which the horsepower rating is multiplied to determine the maximum safe load that a motor may be expected to carry continuously. If a motor has a service factor of 1.25, then it can be loaded up to 25% greater than its rated horsepower. It is a compensation used to insure continued performance of a motor which must operate under varying load conditions. The service factor can be compared to a safety factor or a safety precaution.

Fractional horsepower motors rated 230 volts will operate satisfactorily on 208 volt systems on most applications requiring nominal starting torque. Starting and maximum running torque of a 230 volt motor will be reduced approximately 25% when operated on 208 volt systems. Fans, blowers, centrifugal pumps, and similar loads will normally operate satisfactorily at these reduced torque.

Motors rated at 208-230 volts are designed to operate on systems at plus or minus 10% of rated voltage. Where the application torque requirements are high, it is recommended that the next higher horsepower 230 volt motor or a 200 volt motor be used. External motor controls for 230 volt motors on 208 volt systems should be selected from 230 volt nameplate data.