Voltage drop

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hhsting

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Glen bunie, md, us
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Junior plan reviewer
I have 125A fused disconnect whose load side phase and neutral conductors are size 4#1 at 480/277V three phase which go 250 feet.

I am confused based off of 250.122(B) would the equipment grounding conductor be sized at #6 or higher?
 
The way I see this your conductors are #1, so 75c ampacity is 130A, the next size smaller is #2 whose 75c ampacity is 115A which means it does not have sufficient ampacity (w/out other rules being used) for the 125A breaker. You are using the smallest size conductor so #6 or larger if you please for the EGC.
 
My concern:

Under normal condition without voltage drop I can use phase conductor #2 since fuse is less than 800A and next standard size of #2 AWG ampacity of 115A per 240.6(A) NEC 2014 is 125A. However due to voltage drop it is increased to phase conductor #1.

Now my EGC must be increased as well instead of #6 as minimum should it not be #4 minimum based off of 250.122(B) NEC 2014?
 
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The EGC must increase as stated in 250.122

Roger
 
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