PE Power exam NEC question

What is the maximum rating of the Inverse Time Breaker to be used for the short-
circuit and ground fault protection of a branch circuit supplying a 3-phase, 50 hp, 460 V

wound rotor induction motor?

A. 90 A

B. 100 A

C. 150 A

D. 175 A


Considering 65A based on Table 430.250, I selected option A as the answer based Table 430.52 - Maximum Rating or setting of branch circuit short circuit and ground fault protective devices for wound rotor - Inverse time breaker. (65 * 1.5) = 97.5 A.

Unfortunately, as per the solution index, its the wrong answer. If it says maximum setting, then going by the rule, we cannot go beyond 150 % of the FLC.

Can someone please help interpret the table.

Thanks in advance.

Is the correct answer (B)? Although NEC indicates the maximum rating for this particular instance, NEC also allows for the use of the "next higher standard size" circuit breaker when it comes to maximum.

knight1fox3 said:

Is the correct answer (B)? Although NEC indicates the maximum rating for this particular instance, NEC also allows for the use of the "next higher standard size" circuit breaker when it comes to maximum.

Click to expand...

Yes, the correct answer is B. Somehow didn't interpret the table correctly.