oversized grounded conductor

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Dennis Alwon said:
I find this to be a terrible install but cannot find an article that disallows it.
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Why? I just look at it as an extension of the panels neutral bar. That said, I haven't done it but can see the benefits of less wires in the conduit to mess with.

However, I do it all the time with ground wires by adding ground bars in j-boxes, gutters, etc.
 
roger said:
commonneutral.JPG
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How does one handle-tie the breakers?
 
Ir seems like one could argue that the grounded conductors of the individual circuits do not originate in the same panel as the ungrounded circuits, especially if one consideres the 'super-neutral' an extension of the neutral bus.
 
Dennis, there are actually four MWBC's shown, 1-3, 5-7, 2-4, and 6-8. If these were not MWBC's the common grounded conductor would have to be a 160 amp conductor in lieu of the 80 amp conductor shown.

Roger
 
roger said:
Dennis, there are actually four MWBC's shown, 1-3, 5-7, 2-4, and 6-8. If these were not MWBC's the common grounded conductor would have to be a 160 amp conductor in lieu of the 80 amp conductor shown.

Roger
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I see what you are saying but I don't see the definition of MWBC satisfied by this layout.

Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.
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Using one neutral I see the definition as requiring voltage between all the ungrounded conductors. I also don't see how the intent of 210.4(B) is satisfied.
 
Cow said:
Why? I just look at it as an extension of the panels neutral bar. That said, I haven't done it but can see the benefits of less wires in the conduit to mess with.

However, I do it all the time with ground wires by adding ground bars in j-boxes, gutters, etc.
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Let me rephrase-- I do not see how this install can be compliant with 210.4(B).
 
I didn?t read every post completely but did scan them a little.

If these branch circuits are installed on the inside of the building then Article 225 would not apply as 225 is for feeders and branch circuits installed outside.

Section 215.4 addresses feeders with a common neutral but does not address branch circuits with a common neutral as branch circuits installed inside are covered in Article 210.
 
Dennis Alwon said:
I see what you are saying but I don't see the definition of MWBC satisfied by this layout.


Using one neutral I see the definition as requiring voltage between all the ungrounded conductors. I also don't see how the intent of 210.4(B) is satisfied.
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Dennis, circuits 1-3, 5-7, 2-4, and 6-8, all meet the definition of a MWBC

Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.
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Roger
 
roger said:
Dennis, circuits 1-3, 5-7, 2-4, and 6-8, all meet the definition of a MWBC.
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I disagree. I think none of them do. If I open both breakers 1 and 3, there will still be current flowing in the neutral wire that is part of circuit 1-3. Thus, the set (wire 1 + wire 3 + the neutral) does not comprise a single circuit.

This takes me back to my earlier comment. If there is a hazard involved in a MWBC, such that we have to use handle ties for a MWBC, then how can that same hazard not exist in the situation depicted in the Handbook figure you posted?

 
charlie b said:
I disagree. I think none of them do. If I open both breakers 1 and 3, there will still be current flowing in the neutral wire that is part of circuit 1-3.
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Correct, but it will not be current from breakers 1 and 3, so this set of conductors, ungrounded 1, 3, and the neutral, still meets the definition of a MWBC. Current is not part of the definition although voltage is.

charlie b said:
Thus, the set (wire 1 + wire 3 + the neutral) does not comprise a single circuit.
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And I disagree with this.



charlie b said:
This takes me back to my earlier comment. If there is a hazard involved in a MWBC, such that we have to use handle ties for a MWBC, then how can that same hazard not exist in the situation depicted in the Handbook figure you posted?
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It does exist, but it is a permissable wiring method regardless.

Roger
 
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roger said:
Correct, but it will not be current from breakers 1 and 3, so this set of conductors, ungrounded 1, 3, and the neutral, still meets the definition of a MWBC. Current is not part of the definition although voltage is.
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Turn off both circuit breakers for a single circuit (of the multi wire variety), and one of the conductors related to the circuit still carries current. I can't get there.:-?

The general rule of thumb that "what is not disallowed is allowed" cannot be used here. 210 specifically says that branch circuits must be installed in accordance with that article. Nothing in that article allows the same wire to be used for more than one branch circuit. 210.4 lets us share a grounded wire with two or three ungrounded, but it still calls it a single circuit. You are speaking of four circuits sharing the same grounded conductor. I call that a violation of 210.
 
charlie b said:
The general rule of thumb that "what is not disallowed is allowed" cannot be used here.
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Charlie, that "general rule" doesn't have to used here as long as 225.7 is included in the NEC.

Remove 225.7 and you have an argument.

Roger
 
roger said:
Remove 225.7 and you have an argument.
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Not at all. As Mike pointed out, 225 has a limited applicability that does not include the present discussion. The fact that something is allowed under 225.7 does not mean that the same thing is allowed everywhere else. Perhaps there is something special about outdoor lighting. Perhaps there is an expectation that you don't want to waste copper installing separate neutrals, since each will have a long run from the panel to the first light. But the reason 225.7 allows something does not matter. It does not change the fact that 210 says to follow 210, and that 210 does not say it's OK to share conductors between separate circuits.
 
charlie b said:
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The general rule of thumb that "what is not disallowed is allowed" cannot be used here. 210 specifically says that branch circuits must be installed in accordance with that article. Nothing in that article allows the same wire to be used for more than one branch circuit. ...
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And nothing tells me I can't use the same wire for more than one branch circuit.
 
For what it is worth, in the Nov. 2009 issue of EC&M there is a section that is called "Stumped by the Code? by Mike Holt. Here is what I found

Q. Does the code address sharing a neutral for two conductors of the same phase?

A. Not really, Section 310.10 is the closest you'll find, which says conductors must not be used where the operating temperature exceeds that designated for the type of insulated conductor involved. With that said, it would be legal to do this, if the neutral was big enough.
 
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