What does service factor on a motor indicate?

• A. How far beyond its official nameplate power rating a motor can be driven before overheating
• B. It's the efficiency rating
• C. It's the maximum ambient temperature rating
• D. It's the overload protection setting

Answer: (A)

The service factor is a thermal margin that shows how much extra load a motor can handle above its nameplate rating without overheating, under the specified cooling and ambient conditions. It’s a multiplier on the rated horsepower or torque, so a motor with a 1.15 service factor can temporarily deliver about 15% more power than its nameplate rating. This extra capacity is intended for short-term overloads or peak loading, not for continuous operation. It is not related to efficiency, ambient temperature rating, or the protection settings, which is why the correct interpretation is that the motor can be driven beyond its official rating for limited periods before overheating.