ECN Forum Forums Code Related Discussion NEC & other Code issues Sizing Neutral

You might want to look at 250.24, 250.26 and table 250.66 - you can't have that much of a difference in size between phase conductors and your grounded conductor (neutral)

Don
' If nothing else yer interesting ?? Where do you come up with this stuff I said No such thing?? I also refered you to 250.24b1 if I recall. Like I said veryyyyyy interestingggggggg

Kenny,
That would be true if we were talking about a service, but the original post specified a sub-panel and those sections do not apply. For a feeder the neutral only has to be sized for the maximum unbalanced load. My example of 500 kcmil ungrounded conductors and a #12 grounded conductor is code compliant for a feeder with the types of loads that I specified.
Don

Don- I agree with you 100%. Thats why I said we need to know the load. And Yooper, Your a sharp code man but you blew it on this one. There was a time you could only reduce the neutral 2 sizes but that rule went bye bye. Now like Don says, the grounded conductor has to be large enough to carry the neutral load plus if it's a service panel, it can't be smaller than the GEC. There is allowable reductions after 200a though like you said.

[This message has been edited by George Little (edited 10-22-2004).]

[This message has been edited by George Little (edited 10-22-2004).]

Daaaa
So you agree with Don 500 mcm with #14 netural????? Remember I always Did refer you to 250.24b.And also 250.122 gives equipment gr. size Which means 500 mcm ungrounded conductors (400amp) with #14 neutral and a #2 .copper equipment ground?? ummmm maybe we're talking about didfferent things here???Question Outright Can a Neutal be reduced under 200 amps??

Yes

Yooper- I think we might be talking about 2 different animals. If we are talking about Service- then the grounded/grounding conductor are the same conductor and the conductor might be asked to conduct fault current at the service level, which would exceed Don's 20a. If we are talking about a sub panel, then the grounding conductor must comply with 250.122 because it would be expected to conduct current to trip the subpanel main overcurrent device. But the grounded conductor only has to be large enough to serve the maximum unbalance that could be imposed on the load- in Don's sample the maximum would be 20a. IMHO

[This message has been edited by George Little (edited 10-22-2004).]

George, nice post, I agree entirely. I came back to this thread when I realized Yopper might have missed that the opening question was about a sub panel not a service panel.

Bob

Thanks for the input guys. Yes it is a subpanel in question. I will have a maximum of 30 amps unbalanced load on the neutral at this point. So if I wanted to, I could feasibly use a # 10 neutral, though I won't for future expansion sake. I believe I got it straight now, and it's helped me tremendously to understand the difference between the service and feeder conductor requirements for neutrals.. Steve

I need to ask again is the supply to the service that supplies this panel single phase or three phase. A single phase feeder that is supplied from a three phase wye connected service will have as much current on the neutral as on the most heavily loaded phase conductor. The neutral currents in a single phase feeder that is supplied from a three phase wye connected service DO NOT CANCEL.
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Tom H