Multi wire circuits

[George Stolz]

I think you guys are reading too fast

this has nothing to do about the neutral or EGC, and he doesn't mention that the #10 was ran for voltage drop, it might have just been what was already installed and wants to use it? I don't see anything in the NEC that would prevent him from using two #12 phase conductors and a #10 phase conductor to feed the hots to a MWBC circuit.

Sure now if this #10 was run for voltage drop then that is another issue if not run in a metal raceway.

Wow using a requirement for the EGC for a neutral then using a rule for a feeder for a branch circuit?

talk about mixing apples and oranges:lol:

Wayne, they are right, the code is inconsistent between branch circuits and feeders. A feeder neutral can't be smaller than required by 250.122 to cover short circuit current. By all rights, the branch neutral should be no different. The EGC would have to be #10 per 250.122(B), regardless of the reason for the #10 phase conductor. That's been true for several cycles.

 

[hurk27]

Wayne, they are right, the code is inconsistent between branch circuits and feeders. A feeder neutral can't be smaller than required by 250.122 to cover short circuit current. By all rights, the branch neutral should be no different. The EGC would have to be #10 per 250.122(B), regardless of the reason for the #10 phase conductor. That's been true for several cycles.

And this would be true for an EGC as I pointed out in post #11 if this circuit wasn't in a metal raceway, but I find no such requirement for a grounded (neutral) conductor which was the question that was inserted into the OP.

 

[hurk27]

The neutral must be a 10 as well. If you increased for voltage drop they must increase as well and also isn't the neutral required to be at least the size of the ground wire?? making it a 10 also.

Something to think about:
to the above in red:

If the above in red was ever made true, just think how big our grounded conductors would have to be to be equivalent to the current capability of a metal raceway?

 

[George Stolz]

And this would be true for an EGC as I pointed out in post #11 if this circuit wasn't in a metal raceway...

It doesn't matter if the raceway is metal or not. If an EGC of the wire type is installed in that metal raceway, it is required to be increased in size proportionately to the phase conductors.

, but I find no such requirement for a grounded (neutral) conductor which was the question that was inserted into the OP.

For branch circuits, no - but for feeders it is required to upsize the neutral proportionally just like an EGC in 215.2(A)(2).

If the above in red was ever made true, just think how big our grounded conductors would have to be to be equivalent to the current capability of a metal raceway?

We don't have to increase the neutral and EGC to match each other (as in, a math problem based exclusively on neutrals and grounds) - all calculations are based on the ungrounded conductors. If the ungrounded conductor increases in size, then the EGC increases in size because 250.122(B) tells us to. If the neutral conductor is a feeder neutral conductor, then it too increases in size because 215.2(A)(2) tells us to. In each case, it is a separate math problem based on the ungrounded conductors that starts the ball rolling.

I believe Barndog was speaking of the wire type EGC in his post.

 

[hurk27]

It doesn't matter if the raceway is metal or not. If an EGC of the wire type is installed in that metal raceway, it is required to be increased in size proportionately to the phase conductors.


For branch circuits, no - but for feeders it is required to upsize the neutral proportionally just like an EGC in 215.2(A)(2).


We don't have to increase the neutral and EGC to match each other (as in, a math problem based exclusively on neutrals and grounds) - all calculations are based on the ungrounded conductors. If the ungrounded conductor increases in size, then the EGC increases in size because 250.122(B) tells us to. If the neutral conductor is a feeder neutral conductor, then it too increases in size because 215.2(A)(2) tells us to. In each case, it is a separate math problem based on the ungrounded conductors that starts the ball rolling.

I believe Barndog was speaking of the wire type EGC in his post.

I see this wording was put into 215.2(A)(1) just after the exceptions in 2005, and moved to 215.2(A)(2) in 2011, prior to that the only place it was mention was 250.32(B)(2) for feeders to a separate building.

while this has an effect on conductors for feeders on circuits 30 amps or less it still allows some neutral reduction after this point.

But I do see the point and had never thought about it since it would be rare to run feeders less then 30 amps, and in 2002 and prior it wasn't allowed for more then two branch circuit on the load side of the feeders, Ironically enough this was in the same section area: 215.2(A)(2) but was removed in 2005.