If a motor has a service factor of 1.15 and is rated at 10 HP, what is the maximum continuous horsepower it can deliver under proper conditions?

• A. 12 HP
• B. 10 HP
• C. 9 HP
• D. 11.5 HP

Answer: (D)

Service factor tells you how much overload the motor can safely deliver above its rated horsepower, provided it’s kept cool and operated under the specified conditions. With a rated horsepower of 10 HP and a service factor of 1.15, the maximum continuous power the motor can deliver is 10 × 1.15 = 11.5 HP. This is the amount you can maintain under proper cooling because the service factor defines that allowable overload.

So, the motor can continuously deliver 11.5 HP under the proper conditions. The other numbers don’t fit because they either ignore the overload (10 HP), fall below the rated load (9 HP), or assume a higher overload (12 HP) that requires a service factor of 1.2.