ECN Forum Forums Code Related Discussion NEC & other Code issues 210.19 exc#2

You have to look at the connected load. If a significant part of the connected load is line to line only you can safely downsize the neutral but since (2005?) they say in addition to the 220.61 calculation (to provide overload protection), 250.122 will be the minimum size (to provide short circuit protection).

Greg,
If we are saying that the neutral conductor is required to be protected at or below its ampacity per the rules in 240, there is no way that we can use a "downsized" neutral for a feeder, no matter what the rules in the other code sections say.

It all depends on what you are protecting it from. If you are talking about "overload" then 310.15 rules and that is the case when you size to line to neutral loads. If you are just protecting it from a line to neutral fault that is short circuit protection and you can use 250.122.
When you think about it, we don't seem to have a problem sizing EGCs with 250.122 and that is sufficient to clear a ground fault.
I agree there was a problem when they only used 220.61 and you could end up with a very small neutral that might not clear a bolted L/N fault.

Greg,
I am talking about 240.4 which requires the conductors to be protected at their ampacity. I guess my point should be, contrary to what I said before, that Article 240 should be changed to make it clear that it only applies to ungrounded conductors. An undersized feeder neutral as permitted by the code rules is not protected per 240.4.

I agree, you have found a hole in the code. They should either add "feeder neutrals" to 240.4(G) table or remove 220.61.
I am going to bounce this off of the Fl IAEI group and see if we are missing something.

Don I am trying to defend your position over at Fla IAEI and they keep telling me 240.4 dies not apply to neutrals. I point out it doesn't say that.

http://www.iaeifl.org/forums/ubbthr..._there_a_conflict_between_22.html#UNREAD

Greg,
Maybe it shouldn't apply to neutrals, but the wording only says "conductors" must be protected. I don't know how you can have a neutral that is not a conductor.

I think that this is just one more of those cases where the code doesn't really say what the writers thought it did. I don't think Article 240 is intended to apply to neutrals, but the wording makes it apply.

Greg,
Maybe it shouldn't apply to neutrals, but the wording only says "conductors" must be protected. I don't know how you can have a neutral that is not a conductor.

I think that this is just one more of those cases where the code doesn't really say what the writers thought it did. I don't think Article 240 is intended to apply to neutrals, but the wording makes it apply.

You convinced me but I think it is just a hole in the code. I still think the neutral is protected against overload by 220.61 and against short circuit by 250.122 but 240.4 does not say that.