Sizing Motor supply EGC

[Pierre C Belarge]

I did not search this site, sorry if this has been discussed.

430.245 states to follow Part VI of Article 250 for method of grounding.

In Part VI or Article 250:

250.122(D)(1) General. The equipment grounding conductor size shall not be smaller than determined by 250.122(A) based on the rating of the branch-circuit short-circuit and ground fault protective device.


If one was to install a protective device as per 430.52(C)(1) Exception 2 for instance. Say a 100A rated motor using a nontime-delay fuse (which would permit the overcurrent protective device to 400%), would one not be required to upsize the the EGC (copper)? From an 8Awg to a 3 Awg

Thanks for the help!

 

[ActionDave]

Hey! Welcome back.

Back up a little bit and look at 250.122 (A).

 

[david luchini]

Yes, I believe your scenario would require a #3 cu EGC.

(I don't see anything in 250.122(A) that would change that requirement.)

 

[ActionDave]

,but in no case shall they be required to be larger......?

 

[david luchini]

,but in no case shall they be required to be larger......?

I don't see that a #3 AWG EGC would be larger than #1 AWG supply conductors.

 

[ActionDave]

I don't see that a #3 AWG EGC would be larger than #1 AWG supply conductors.

You have to start at 430.52. You don't need 100A wire

 

[david luchini]

You have to start at 430.52. You don't need 100A wire

:?

You need a wire with an ampacity not less than 125% of the motor full load current (from 430.22, not 430.52.)

That would be 125A, which would be #1 AWG. So the motor in the example would need #1 AWG supply conductors and a #3 AWG EGC.

 

[ActionDave]

Ahhhhh. Uggggg. I was reading too fast and only thinking about being allowed to use a larger over current device on smaller wires.

Shouldn't be on my phone at work but hey it was cover break time. I'll ponder this more later.

 

[ActionDave]

So the right thing to do is read the whole question and read the whole relevant code section.

Mostly was glad to see Pierre pop up on the forum and got a little giddy. Now he seems to have gone missing again. Sigh.