Motor branch circuit overcurrent protection and wiring

[Akten]

Hi,

I have to select conductor size and OCPD for motor branch circuit. The motor is 20hp at 480V 3ph.

If I select 70A Short circuit/Ground Fault protection device based on 430.52, is #10 awg conductor still acceptable per NEC (it meets the min ampacity requirement for this motor FLC) ,or will it not meet the conductor overcurrent limitation per 240.4(D)?

I think the exception is 240.4 (G) allows me to proceed with my selection (#10 awg and 70A breaker) but hoping to get some opinion here. Thanks

 

[infinity]

So the FLC from 430.250 is 27 amps. 27*125%=33.75 amps which is your minimum conductor size. #10 AWG @ 75° C is 35 amps so that's good. 240.4(D) does not apply. Inverse time CB 27*250%=67.5 amps next size up 70 amps.

 

[Dennis Alwon]

Hi,

I have to select conductor size and OCPD for motor branch circuit. The motor is 20hp at 480V 3ph.

If I select 70A Short circuit/Ground Fault protection device based on 430.52, is #10 awg conductor still acceptable per NEC (it meets the min ampacity requirement for this motor FLC) ,or will it not meet the conductor overcurrent limitation per 240.4(D)?

I think the exception is 240.4 (G) allows me to proceed with my selection (#10 awg and 70A breaker) but hoping to get some opinion here. Thanks

You are correct 240.4(G) allows you to use #10 at a higher amp than 240.4(D) will allow