What is the maximum overload protection size for a 208-Volt, single-phase, 3-horsepower motor marked with a 1.1 service factor and a nameplate current of 16 amperes, based on 430.32(A)?

• A. 20 A
• B. 16.7 A
• C. 18.4 A
• D. 25 A

Answer: (C)

Sizing motor overload protection follows a straightforward rule: use 115% of the motor’s full-load current (FLC) as the maximum rating for the overload protective device. The nameplate current given is the full-load current, 16 A. Multiply by 1.15 to get 18.4 A.

So, the maximum overload protection size is 18.4 A. The service factor (1.1) does not change this calculation for the overload device sizing; it mainly indicates how much extra load the motor can handle beyond its rated horsepower, not how the overload protector is sized. The other values correspond to either higher percentages (which would exceed the limit) or nonstandard steps, while 18.4 A aligns with the 115% rule.