[donf]

Greetings.

I'm 200+ pages into an electrical book that I am editing and I hit a question that I believe is poorly written.

Regarding NEC Table 430.250 and Article 430.52 exception (1)

The question:

"What size branch-circuit conductor and overcurrent device (circuit breaker) is required for a 7.5 hp 230V, three phase motor with 75C terminals?

The correct answer is given as: 10 AWG conductor with a 60A "inverse time breaker."

My concern with this question is that, the surrounding text discussion has zero information on selecting the type protection device. No information is given to usersregarding Table 430.52 and no process for selecting the device type is given.

To me, this question's answer should be limited to the size of the conductor as well as the size of the breaker or add the description of how make the proper device selection.

Agree / disagree?

[tkrussell]

Sorry Don, for delay in getting to this question.

I agree to the latter, since choosing the exact type of OCPD is required before sizing that device, since Table 430.52 lists two types of circuit breakers, instantaneous and inverse time, and each has it's own specific rating.

The question needs to have added ("inverse time" circuit breaker), since the required answer is related to ITCB.