Minimum Size Grounded Conductor for a Branch Circuit

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Dennis Alwon

Dennis Alwon

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I know that article 215.2(A)(1) states the minimum size grounded conductor for a feeder cannot be smaller than the egc-- next to last paragraph.

My question is where does the NEC state the same for a branch circuit? Logic tells me the grounded conductor must not be smaller than the egc but I cannot find it. Thus if you have a range- can the grounded conductor be a #12 if the egc is #10? I say no but I am being challenged on it and I cannot support my claim. For this situation we will assume a #12 is sufficient for the load.
 
Dennis Alwon said:
I know that article 215.2(A)(1) states the minimum size grounded conductor for a feeder cannot be smaller than the egc-- next to last paragraph.

My question is where does the NEC state the same for a branch circuit? Logic tells me the grounded conductor must not be smaller than the egc but I cannot find it. Thus if you have a range- can the grounded conductor be a #12 if the egc is #10? I say no but I am being challenged on it and I cannot support my claim. For this situation we will assume a #12 is sufficient for the load.
Click to expand...

For household ranges and cooking appliances check out 210.19(A)(3) Exception #2.

Exception No. 2: The neutral conductor of a 3-wire
branch circuit supplying a household electric range, a
wall-mounted oven, or a counter-mounted cooking unit
shall be permitted to be smaller than the ungrounded conductors
where the maximum demand of a range of 83⁄4-kW
or more rating has been calculated according to Column C
of Table 220.55, but such conductor shall have an ampacity
of not less than 70 percent of the branch-circuit rating and
shall not be smaller than 10 AWG.
Click to expand...

Chris
 
raider1 said:
For household ranges and cooking appliances check out 210.19(A)(3) Exception #2.

Chris
Click to expand...
Thank's Chris...
So the grounded conductor can't be less than #10 so it won't be smaller than the EGC. What about in general-- Is there anywhere in the NEC that states the grounded conductor for a branch circuit cannot be smaller than the EGC.
 
Dennis Alwon said:
Thank's Chris...
So the grounded conductor can't be less than #10 so it won't be smaller than the EGC. What about in general-- Is there anywhere in the NEC that states the grounded conductor for a branch circuit cannot be smaller than the EGC.
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I am not aware of a general requirement for a branch circuit neutral to be larger than the required EGC.

The general rule in 210.19(A) pretty much will require a neutral conductor the same size as the ungrounded conductors which would make it the same size or bigger than the egc.

Chris
 
raider1 said:
The general rule in 210.19(A) pretty much will require a neutral conductor the same size as the ungrounded conductors which would make it the same size or bigger than the egc.

Chris
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I don't see where 210.19(A) states that at all. It doesn't mention grounded conductor except for the exception #2 but wouldn't the load be the line to neutral load?

It just seems odd to me that it is possible to run a piece of equip. that is 240V say 60 amps and has a neutral load of say 5 amps. and have a neutral smaller than the egc.

It appears the NEC requires a ground of #10 so that the 60 amp breaker can trip safely on ground fault but then allows a #12 for a grounded conductor. What happens with a line to neutral short.

Let's exaggerate the situation with a piece of equip. at 100 amps needing a #8 EGC but a grounded conductor of #12. Seems wrong.
 
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I don't see a relationship between the grounded (or neutral) conductor and the equipment grounding conductor. I don't see it for a feeder, and therefore don't understand the requirement that you cited in post #1. I don't see it for a feeder either. If there is a fault, the neutral conductor will not be a player in the events that follow. Current in the neutral wire will not proceed through the fault point. Rather, current from one or more of the ungrounded conductors, having gotten their energy from the source, will transmit that energy back to the source via the fault point and via the EGC. Why should the size of the neutral have anything to do with the size of the EGC? What am I missing here? :confused:
 
charlie b said:
I don't see it for a feeder, and therefore don't understand the requirement that you cited in post #1. I don't see it for a feeder either.
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From 215(A)(1), after the exceptions.

The size of the feeder circuit grounded conductor shall
not be smaller than that required by 250.122, except that
250.122(F) shall not apply where grounded conductors are
run in parallel.
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charlie b said:
What am I missing here?
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Perhaps this is what I missed:
Dennis Alwon said:
What happens with a line to neutral short.
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OK, so that is why, for a feeder, you need a neutral wire at least as big as the EGC - to facilitate a breaker trip in the event of a L-N fault. So why not also on a branch circuit? Do I now, finally, understand the original question? :cool:
 
Uh, sorry guys; perhaps a poor choice of words on my part. I saw 215(A)(1), so I did "see" the requirement. What I was trying to say is that I did not "see the need for" the requirement, because I did not see a relationship between the neutral and the EGC, as far as sizing is concerned.
 
charlie b said:
Uh, sorry guys; perhaps a poor choice of words on my part. I saw 215(A)(1), so I did "see" the requirement. What I was trying to say is that I did not "see the need for" the requirement, because I did not see a relationship between the neutral and the EGC, as far as sizing is concerned.
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Yes, you got the idea now.

What is the purpose of reqiuring Table 250.122 to be used? I believe it is to clear ground faults safely. If there is a neutral to hot short and the neutral is say a few sizing smaller than the EGC isn't possible the short may not trip the breaker? If not then why requie larger egc's for larger breaker sizes?
 
Bump-- anybody else care to go after this one. The question is well put by Charlie. It is hard to imagine the NEC has missed this one for all these years.

OK, so that is why, for a feeder, you need a neutral wire at least as big as the EGC - to facilitate a breaker trip in the event of a L-N fault. So why not also on a branch circuit? Do I now, finally, understand the original question? :cool:
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iwire said:
Can you give an example of a branch circuit where the neutral could be smaller than the EGC?
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That was my point with stating that the general requirements in 210.19(A)(1) would require a full sized neutral for a 2 wire branch circuit or a multiwire branch circuit that only serves line to neutral loads.

The Exception that I pointed out in 210.19(A)(3) covers household cooking equipment.

Chris
 
I think I have it. :)
raider1 said:
The general rule in 210.19(A) pretty much will require a neutral conductor the same size as the ungrounded conductors which would make it the same size or bigger than the EGC.
Click to expand...
No, the neutral can be smaller than the phase conductors, but not by much. We have to add 25% of the continuous load, when sizing the phase conductors, per 219.(A)(1). But we don?t have to add the 25%, when sizing the neutral, as allowed under Exception 2. So the neutral can be smaller, and I would bet (without trying any examples to make sure) that this 25% difference would never allow the neutral to be smaller than the EGC.
Dennis Alwon said:
I don't see where 210.19(A) states that at all. It doesn't mention grounded conductor except for the exception #2 but wouldn't the load be the line to neutral load?
Click to expand...
No it is not the line to neutral load, nor the maximum imbalance load. I believe you are thinking in terms of calculating a neutral load that is much smaller than the phase load, and sizing a conductor for that load. You cannot do that calculation for branch circuits, and therein lies the answer to your original question. Have a look at 220.61. It speaks only of feeders and services. There is no similar calculation of a neutral load for branch circuits. That is why 215.2(A)(1) has to have a lower limit for the neutral wire, so as to allow the neutral to carry the same amount of current (in a L-N fault) that the EGC would carry (in a L-G fault).
 
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charlie b said:
I think I have it. :)
No, the neutral can be smaller than the phase conductors, but not by much. We have to add 25% of the continuous load, when sizing the phase conductors, per 219.(A)(1). But we don’t have to add the 25%, when sizing the neutral, as allowed under Exception 2. So the neutral can be smaller, and I would bet (without trying any examples to make sure) that this 25% difference would never allow the neutral to be smaller than the EGC.
Click to expand...

Correct, my assertion was that even with the 25% allowance most likely it would not work out that the neutral would be a smaller conductor than the ungrounded conductor.

Chris
 
If I'm understanding correctly and I did the math right

at 60 amps would need #6 if you add 25% for continuous load that would increase the amperage to 75 amps which would be #4 so still a #6 for the grounded conductor and at 60 amps you can use a #10 as the EGC.

Am I understanding that right? Just an example above.
 
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