Previous Tips of the Month from Rantro.
The service factor of a motor is a number, which indicates how much more work a given motor can do beyond the rated horsepower.
This is a safety factor and is not to be considered as a part of the motors normal useful horsepower. A motor may have no service factor whatsoever and thus has no safety factor in the event the motor becomes overloaded.
A common service factor on motors is a SF of 1.15. This number multiplied times the rated horsepower of that motor gives the actual horsepower that motor could operate at in an emergency.
For example; a 10 HP motor with a SF of 1.15 could actually provide service for a short time up to 11.5 HP.
A motor with a high service factor is used on applications where the load may vary and may occasionally be confronted with an unexpected overload in horsepower. Air conditioning systems often use motors with the SF rating of 1.15.
The service factor can also be multiplied times the FLA of the motor to give the absolute highest operating amperage the motor should be allowed to operate with.
This use of the service factor is not recommended, as it is not completely reliable as it assumes the voltage the motor is getting is exactly correct. This is also a poor service practice because it encourages technicians to allow loading motors up into the safety zone erasing the safety zone that the service factor is intended to provide.
