SUB PANEL IN SAME BIDG 3-WIRE

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diggers

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I talked to an elec contractor a few days ago and he said it is allowable to run a 3-wire feeder to a sub panel as long as it's in the same bldg. He said he found a code on it but couldnt specify were in the code book. Anybody know the code?
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Yeah this guy comes up with all kind of strange allowable circumstances in his book.
I always run 4-wire to any sub panel either in same bldg or not.

How about this one:
He says he will also run only 3-wire to a sub panel if it only feeds 220V circuits.
I disagree with this also as it may be used in the future for a 120V circuit somewere.
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Originally posted by diggers:
I disagree with this also as it may be used in the future for a 120V circuit somewere.
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Actually, I don't see any code that forbids that.
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Originally posted by peter d: It's not allowable, and the code that forbids this is 250.142(B)
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We don't know that. You interpreted the "3-wire feeder" to mean that the neutral wire is being used as both a neutral and an EGC. That would be forbidden, as you pointed out.

But did the statement from the unnamed electrical contractor mean that the 3 wires were phase, phase, and neutral, with the conduit serving as EGC? If that is the intent, then it is legal, at least in some jurisdictions. Other jurisdictions (and some types of projects) force you to install an EGC wire, regardless of the type of conduit being used.
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Charlie, I think you're reading into it too much.

Edit: But if I am wrong I will gladly eat my words and look the fool. :)

[ October 21, 2005, 05:52 PM: Message edited by: peter d ]
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

I'm with Charlie, the original post is vague. Besides a 3 wire feeder could also be 3 wire romex which actually has 4 conductors.
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

How about this one:
He says he will also run only 3-wire to a sub panel if it only feeds 220V circuits.
I disagree with this also as it may be used in the future for a 120V circuit somewere.
Click to expand...
He intends to feed only 2 a.c. units (4-8 space panel), but, if the a.c. units are removed or what have you, then you will have an improper sub panel for 120v/240v. And we all know someone will come along and use it for 120/240.
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Originally posted by infinity:
Does 250.142(B) require a neutral to a sub-panel?
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If we have line-to-neutral loads, we need a grounded conductor. 250.142(B) forbids us from using the grounded conductor for equipement grounding. Therefore, we must run an EGC for a "sub panel"

There are exceptions to this rule of course, the two mains ones are feeding an exterior building, and of course the 3-wire dryer and range circuits.
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Originally posted by diggers:
He intends to feed only 2 a.c. units (4-8 space panel), but, if the a.c. units are removed or what have you, then you will have an improper sub panel for 120v/240v. And we all know someone will come along and use it for 120/240.
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I just installed such a system in a warehouse, aq 120' run, where only the outside AC unit and inside air handler w/strip heat are fed. The advantage is that there is a #2 al SE cable that has a maximum load of 48 amps at any given moment, for lower voltage drop.

Plus, this ended up being easier to run and less expensive than a 6-2 cu and a 10-2 cu run over the same distance would have been.

There's always the chance that someone may come along in the future and do something improperly. We can only do but so much. A qualified electrician would look in the panel and say that he cannot supply a line-to-neutral load from this panel; anyone else, who knows?
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

We can not worry about what others might do.If all he has is 240 loads then it would be wasting money to run a neutral.No violation till someone adds a 120 circuit.
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Originally posted by peter d:
There are exceptions to this rule . . . of course the 3-wire dryer and range circuits.
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Not for a while. Read 250.134 through 250.142
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Originally posted by LarryFine:
Not for a while. Read 250.134 through 250.142
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I'm aware of that. I was just making the point that they are one of the very few examples where the grounded conductor is permitted to serve as the EGC also, as long as the it's an exsisting installation acoording to 250.142(B)Exception 1.

[ October 21, 2005, 07:58 PM: Message edited by: peter d ]
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Your exactly right (qualified electrician) I live in Florida were a major portion of self employed are "Handy man" licensed and "Appliance' carded. They like to try to be electricains. I can go for hours on that subject but, anyhow, I see it is accepatable to do this sub system. I am thankfull you guys went over this with me. :D
 
Re: SUB PANEL IN SAME BIDG 3-WIRE

Just so we're clear, if you only have 240 volt loads, you are fine with a 3 wire feed (2 hot, 1 Grounding)

As soon as you have 120 volt loads, you need a 4 wire system with an insulated neutral, and the neutrals and grounds must be separated at the "sub panel."
 
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