# Neutral conductor size drop



## NolaTigaBait

You could only go down to a #10...Whatever the maximum unbalanced load would be is the minimum size, but in that situ. #10 would be the smallest.. Read 220.61


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## Shawn23

NolaTigaBait said:


> You could only go down to a #10...Whatever the maximum unbalanced load would be is the minimum size, but in that situ. #10 would be the smallest.. Read 220.61


 
Thanks. I had read that code before i posted the 1st time but Im not sure how to calculate the unbalanced load? Is there a formula?


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## DCAC

Normally the neutral can go down to 70% of conducters. Whats the unballanced load? And the grounded conducter can not be smaller than the grounding conducter.


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## Dennis Alwon

To size the grounded conductor I would figure all the loads that were 120v. I would try and balance them in the panel and figure what phase would have the greatest load. Thus if I had a 4 circuit panel and all the 120v loads had loads of 5, 10, 12, 8 amps I would put say 5 amps and 12 amp load on one phase and 8 and 10 amp load on the other. so I have 17 on one phase and 18 on the other. I now know that the max load on a phase is 18 amps. One would think that can be my ungrounded conductor current to size the feeder-- BUT we have to be careful because the grounded conductor cannot be smaller than the EGC. So in your case the smallest you can have is a #10 but again figure the neutral load.

If you did a service then the grounded circuit can never be smaller than the GEC.


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## BBQ

I am not sure it is allowable to reduce the neutral supplying a receptacle.

In my opinion when supplying a receptacle the maximum imbalance would be the full circuit rating.


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## BBQ

This section seems to back up my thoughts.




> *551.73 Calculated Load.*
> 
> *(D) Feeder-Circuit Capacity.* Recreational vehicle site
> feeder-circuit conductors shall have an ampacity not less
> than the loads supplied and shall be rated not less than 30
> amperes. The neutral conductors shall have an ampacity not
> less than the ungrounded conductors.


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## NolaTigaBait

BBQ said:


> This section seems to back up my thoughts.


I don't read those sections... Good to know..Thanks bobby


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## Dennis Alwon

BBQ said:


> I am not sure it is allowable to reduce the neutral supplying a receptacle.
> 
> In my opinion when supplying a receptacle the maximum imbalance would be the full circuit rating.


I don't think that is the case of a Range , ovens, etc but I see your point on the mobile home. Of course in the range scenario it is a branch circuit and not a feeder.

I wonder if that is true in general, obviously it is for mobile homes. Good catch


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## BBQ

Dennis Alwon said:


> I don't think that is the case of a Range , ovens, etc but I see your point on the mobile home. Of course in the range scenario it is a branch circuit and not a feeder.
> 
> I wonder if that is true in general, obviously it is for mobile homes.


I really don't know.

It seems to me with a receptacle you could never reduce the neutral size as you never know what may be plugged into it even if it was installed for a specific appliance.


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## Shawn23

This has taught me a lot. It would be nice to know if the comment on not being able to reduce the neutral on any recepticle is a fact or not. That would be easy to remember.


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## HARRY304E

Shawn23 said:


> This has taught me a lot. It would be nice to know if the comment on not being able to reduce the neutral on any recepticle is a fact or not. That would be easy to remember.



Lets say you are wiring a house with romex all the wire come the same size.

so if you wanted to have a smaller neutral you would have to spacial order the wire and that would probably cost more.


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## Dennis Alwon

Shawn23 said:


> This has taught me a lot. It would be nice to know if the comment on not being able to reduce the neutral on any recepticle is a fact or not. That would be easy to remember.


I don't know of any section that specifically states that you cannot reduce the neutral to a receptacle. I do, however agree with Bob as it being not a good idea. Here is what the NEC states. This from 220.61 Feeder or service neutrals



> (C) Prohibited Reductions. There shall be no reduction of the neutral or grounded conductor capacity applied to the amount in 220.61(C)(1), or portion of the amount in (C)(2), from that determined by the basic calculation:
> (1) Any portion of a 3-wire circuit consisting of 2 ungrounded conductors and the neutral conductor of a 4-wire, 3-phase, wye-connected system
> (2) That portion consisting of nonlinear loads supplied from a 4-wire, wye-connected, 3-phase system
> FPN No. 1: See Examples D1(a), D1(b), D2(b), D4(a), and D5(a) in Annex D.
> FPN No. 2: A 3-phase, 4-wire, wye-connected power system used to supply power to nonlinear loads may necessitate that the power system design allow for the possibility of high harmonic neutral-conductor currents.


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## Dennis Alwon

HARRY304E said:


> Lets say you are wiring a house with romex all the wire come the same size.
> 
> so if you wanted to have a smaller neutral you would have to spacial order the wire and that would probably cost more.


I think he is talking about a specific load. Obviously you could not reduce the neutral in a branch circuit for standard rec. unless the breaker was based on the smaller size neutral.


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## Dennis Alwon

Here is the range info.



> 210.19(A)(3)
> 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 8¾-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.


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## Shawn23

Thanks again guys for all the lep. This has been a great code discussion. I am going for my masters in about a month and these are some of the practice questions.


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