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Tuesday, October 5, 2021

Question:

Hello CQD Folks,

I've been told that for a motor circuit, the overcurrent protective device can exceed the ampacity rating of the connected circuit conductors. If this is true and where in the NEC is this allowance stated?

Thanks for any reference you can provide.

Peter Sampson

A

Answer:

Hi Peter,

Thanks for the question. It would be worth it to vision Section 430.6(A) and Example D8 in Annex D. The branch circuit short circuit and ground-fault protective device is permitted to be sized larger to handle motor starting (locked-rotor) current. The Table values are referred to from 430.6(A)(1). It's important to remember that the total overcurrent protection for the motor circuit is the combination of the branch circuit short circuit and ground fault protective device and the require overload protective device for the motor. Check Section 430.52 to see maximum allowable percentages increased based the type of motor branch circuit short circuit and ground-fault protective device. 

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