Subpanel Grounded conductor

[ErikG]

I have a 277/480V subpanel that I want to feed with 200A. The majority of the loads will be 3 phase, and most likely never have any 277v lighting? What is the minimum size grounded conductor I can install?

 

[tom baker]

The EGC side is per 250.122 using the size of the feeder EGC.

 

[AC\DC]

If you have no nuetral loads you don’t need it egc is all you need

 

[augie47]

Minimum groundED see 215.2(A)(2)

 

[James L]

If you have no nuetral loads you don’t need it egc is all you need

Could have no neutral loads on branch circuit but still have neutral load on the feeder, if some loads are [2-pole] single phase.

 

[infinity]

Minimum groundED see 215.2(A)(2)

Augie that's only if you're installing a neutral correct? If there are no 277 volt loads then a 3-wire 480 volt feeder is permitted.

 

[LarryFine]

You don't have to run a neutral unless you need one, but if you do, its minimum required size would be that of the minimum required EGC size, and for the same reason.

Or, of course, that of the greatest calculated possible line-to-neutral load, whichever is greater.

 

[augie47]

Augie that's only if you're installing a neutral correct? If there are no 277 volt loads then a 3-wire 480 volt feeder is permitted.

I thought that was what the OP asked..................

 

[ErikG]

Yes as of now there are no 277v loads. I do want to install a neutral just in case someone in the future would like to pull 277 from this panel. What would the minimum size be?

 

[infinity]

Yes as of now there are no 277v loads. I do want to install a neutral just in case someone in the future would like to pull 277 from this panel. What would the minimum size be?

Augie had it in post #4.

 

[LarryFine]

And I did in #7.

 

[ErikG]

Thanks for the input! I’ve never known 250-122 to be used for anything other than equipment grounding conductor sizing, but 215.2(A)(2) clearly states to use that table for minimum grounded conductor size.

 

[LarryFine]

Thanks for the input! I’ve never known 250-122 to be used for anything other than equipment grounding conductor sizing, but 215.2(A)(2) clearly states to use that table for minimum grounded conductor size.

And again, it's sized that way for the same reason: to assure short-circuit-protection operation.

 

[infinity]

And again, it's sized that way for the same reason: to assure short-circuit-protection operation.

Larry can you explain how the neutral size would be related to short circuit protection? Are you saying a fault between a feeder ungrounded conductor and the feeder neutral?

 

[LarryFine]

Larry can you explain how the neutral size would be related to short circuit protection? Are you saying a fault between a feeder ungrounded conductor and the feeder neutral?

Yes.

 

[infinity]

Yes.

Got it. At first I was thinking about a 277 branch circuit but you're referring to the feeder conductors which makes sense.