multi-circuits on grounded wire

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elmundogrande

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One of my students ask why you can't put 4 circuits on 1 neutral in one conduit into his workshop if phased right with no more than 10amps on any phase at a time so if the neutral is over sized to #10 his case if the loads are balanced at 10 amps and the neutral carries the unbalance it should be at 0amps on the neutral at any time. He thinks you may get up to 20amps on the neutral if all on at the same time and #10 should cover that. What do yall think
 
Sort of like this from the NEC handbook?

commonneutral.JPG



Eight, 20 amp circuits, one neutral.
 
The diagram Bob posted is from Article 225 which says this:

225.1 Scope.
This article covers requirements for outside branch circuits and feeders run on or between buildings, structures, or poles on the premises; and electrical equipment and wiring for the supply of utilization equipment that is located on or attached to the outside of buildings, structures, or poles.
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Now having said that it would appear that Bob's diagram is specific to installations only under the scope of Article 225, however no one has yet to prove that this cannot be installed inside of a building.
 
elmundogrande said:
One of my students ask why you can't put 4 circuits on 1 neutral in one conduit into his workshop if phased right with no more than 10amps on any phase at a time so if the neutral is over sized to #10 his case if the loads are balanced at 10 amps and the neutral carries the unbalance it should be at 0amps on the neutral at any time. He thinks you may get up to 20amps on the neutral if all on at the same time and #10 should cover that. What do yall think
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#10 is good for 30 amps. What if only 2 phases ,both the same phase had 20 amps each ????
 
Jim W in Tampa said:
#10 is good for 30 amps. What if only 2 phases ,both the same phase had 20 amps each ????
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#10 is good for more than 30, but limited to 30 for a number of purposes. What if you say took the whole neutral bar from a panel and put in an enclosure like a gutter 30' from the panel with the feeder for the grounded conductor as say a #2 and 8 20A #12's out to it? Would it operate any different?
 
There is no restriction to how many ungrounded conductors can share a grounded conductor, as long as the grounded conductor is properly sized.

Think of it as similar to a feeder. The grounded conductor supplying the feeders is sized large enough to carry the load imbalance of the ungrounded conductors.
 
While I agree with the statements in this thread that say you can use multiple ungrounded conductors with a single grounded conductor, the members of CMP 2 do not.
2-280 Log #2224 NEC-P02 Final Action: Reject
(215.4)
______________________________________________________________
Submitter: Donald A. Ganiere, Ottawa, IL
Recommendation: Revise as follows:
215.4 Feeders with Common Neutral.
(A) Feeders with common Neutral Two or three sets of 3-wire feeders or two
sets of 4-wire or 5-wire feeders shall be permitted to utilize a common neutral.
(B) In Metal Raceway or Enclosure. Where installed in a metal raceway or
other metal enclosure, all conductors of all feeders using a common neutral
shall be enclosed within the same raceway or other enclosure as required in
300.20.
Substantiation: There is no code violation in using a common neutral so the
specific provision to use one is not required.
Panel Meeting Action: Reject
Panel Statement: The panel disagrees with the submitter’s substantiation.
Section 215.4 (A) is the requirement which limits the number of feeders that
may share a common neutral.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12
______________________________________________________________
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Pierre,
I think that this is one of the cases where the code has attempted to use the words "shall be permitted" in an attempt to prohibit all other uses.
The code does this in a number of cases. I don't think it is a correct use of the phase and see no way that those words that specifically permit something can actually act to prohibit something else. The same thing happens with 310.4. There is no general rule that says you can't parallel conductors, so how does a specific permission to parallel conductors 1/0 and larger act to prohibit paralleling smaller conductors? I had a proposal on that section last cycle too, and panel 6 (proposal 6-8) insists that the works "shall be permitted" actually prohibit all other uses just like panel 2 said in the proposal that I posted in this thread.
We will have a better idea when the ROP comes out as I submitted another proposal to address the common neutral issue.
 
Pierre C Belarge said:
There is no restriction to how many ungrounded conductors can share a grounded conductor, as long as the grounded conductor is properly sized.
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And if 4 circuits are using the same grounded conductor then how would you simultaneously disconnect all the ungrounded conductors? :D
 
Dennis Alwon said:
And if 4 circuits are using the same grounded conductor then how would you simultaneously disconnect all the ungrounded conductors? :D
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If all of the ungrounded conductors are one the same phase, I don't think that there is a code rule that requires a common disconnect.
 
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