Service Factor

June 17, 2024 by
Service Factor

Did you ever think what service factor means for an electric motor?
Service Factor (S.F) is the capability of an electric motor to operate beyond its rated for short periods without any damage to its windings insulation.
Service factor is in a sense, a multiplier greater than 1 and normally within a range of 1.3, though higher values like 1.5 are also there!
Service factor could also be considered as the thermal reserve on the motor windings temperature to take care of extra heat generated due to motor overloading.
For a class F insulation motor with class B temperature rise, there is a thermal reserve of almost 20-25 deg C , to handle extra power and the resultant heat in case the motor was overloaded beyond its rated capacity.
Overloading a motor causes more heat generation and higher temperature rise in the windings (overheating) adversely affecting the motor normal life expectancy.
Unlike what overloading and the resultant overheating is interpreted as drawing more power from the motor shaft, this is not always the case as a motor running at reduced voltage  would draw more current and get overheated with no extra power delivered!
There are other issues like frequency variation, high ambient temperature, frequent starts/ stops of the motor, which could also lead to motor overloading and the service factor to take care of.
A motor with S.F-1.2 though capable of delivering 20% more power continuously; this however would call for correct voltage, fixed frequency, normal ambient / cooling temp., etc.
Generally speaking, service factor, is neither recommended solely for continuous operation, nor increased power to the service factor limit, but a combination of all unfavorable conditions/ factors.