Q. What is the proper size overload, and branch-circuit, short-circuit, ground-fault protective device permitted for a hermetic compressor with a nameplate rated-load of 38A, and a branch-circuit selection current of 40A? The fusible disconnect is going to serve as the disconnecting means, the overload protective device, and the branch-circuit, short-circuit, ground-fault protective device. A) 47.5A
B) 50A
C) 70A
D) 90A
Answer: B
Explanation: As per 440.52(A)(3) of the 2005 NEC, you must use a multiplier of 1.25 (125%) for this calculation.
40 x 125% = 50A
A check of 240.6 reveals that 50A is a standard size ampere rating for fuses and inverse time circuit breakers.
Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at necexpert@aol.com.
