215-4 (a)

[peter]

215.4 [a] states
"(a) Feeders with Common Neutral. Feeders containing a common neutral shall be permitted to supply two or three sets of 3-wire feeders, or two sets of 4-wire or 5-wire feeders."
What is this all about? Why would anyone want to do this? What does it accomplish? Why is it in the Code? Why can't they supply four sets of 3-wire feeders? What dire results would happen if they fed three sets of 4-wire feeders?
~Peter

 

[charlie]

Re: 215-4 (a)

You are asking a lot of questions about just one section.

What is this all about? Why would anyone want to do this? What does it accomplish?

This gives you the ability to save on wire.

Why is it in the Code?

It is in the Code because someone wanted to make this type of installation and the AHJ refused to permit this type of installation. The proposer made a proposal to the NFPA and the Code Making Panel agreed that there was no problem and placed it in the Code. Because it, in fact, didn't cause any problems, it has stayed in the Code.

Why can't they supply four sets of 3-wire feeders? What dire results would happen if they fed three sets of 4-wire feeders?

I don't see any problems, in fact I see advantages since the neutral carries the maximum unbalances current, I think the neutral will be oversized in most cases. If you have a need and the AHJ would permit the installation, I see no reason to stop at two sets of 4-wire feeders. As long as they are controlled and everyone understands what is happening, why not a half dozen? If this is indeed a need, someone would be making a proposal to permit more feeders on a neutral. I doubt that a need exists.

 

[don_resqcapt19]

Re: 215-4 (a)

Charlie,
I'm not sure that this rule is even needed, I don't see any rule that prevents the use of "common" grounded conductors for any type of circuit.
Don

 

[peter]

Re: 215-4 (a)

The way I see this is, say, a 3-wire feeder goes to a big junction box where it is spliced to two [or three] other feeders. Or a four wire feeder [3 phase] does the same thing but can only branch into two separate feeders. Or a five wire feeder [2 phase?] does the same thing.
Is this correct?
Charlie, your explanation of what happened makes sense. Perhaps that "somebody" should have requested the inspector to cite a Code section.
~Peter