# Dumb question about reduced neutral



## subelect (Nov 25, 2007)

The guy who signs my paycheck ran the conduit and got set up to pull a 3 phase, 208 volt ckt to feed a Terminal Box fed from the service entrance (50 amp bkr.) 
He used three #8s for the ungrounded conductors, a #10 EGC and a #10 neutral. 
I could have sworn that the only location that you can legally reduce the neutral conductor is at the service entrance. I thought that all feeders had to have a full-size grounded conductor, even if it is way over-kill. 
The neutral loads are going to be 6 fluor. fixtures, one GFCI and two 110 volt contactors; well within ampacity of #10. 
I just don't want to put up with the hassle when AHJ makes us install a full-sized neutral. 
Is a feeder neutral allowed to be reduced?
Thanks,
Rick


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## HARRY304E (Sep 15, 2010)

subelect said:


> The guy who signs my paycheck ran the conduit and got set up to pull a 3 phase, 208 volt ckt to feed a Terminal Box fed from the service entrance (50 amp bkr.)
> He used three #8s for the ungrounded conductors, a #10 EGC and a #10 neutral.
> I could have sworn that the only location that you can legally reduce the neutral conductor is at the service entrance. I thought that all feeders had to have a full-size grounded conductor, even if it is way over-kill.
> The neutral loads are going to be 6 fluor. fixtures, one GFCI and two 110 volt contactors; well within ampacity of #10.
> ...


NO it is not.


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## rdr (Oct 25, 2009)

If anything seen it upsized where more than one circuit share it but never reduced. Logically, shouldn't be allowed. :blink:


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## TOOL_5150 (Aug 27, 2007)

You can have a reduced neutral in a feeder. You dont even have to run a neutral to a panel that will have all line to line loads. If later down the road someone wants to run a line to neutral circuit, then they would have to pull in a correctly sized feeder neutral.


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## BBQ (Nov 16, 2010)

TOOL_5150 said:


> You can have a reduced neutral in a feeder. You dont even have to run a neutral to a panel that will have all line to line loads. If later down the road someone wants to run a line to neutral circuit, then they would have to pull in a correctly sized feeder neutral.



That is correct.


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## BBQ (Nov 16, 2010)

Here is the relevant code section, note that it applies to services and feeders.



> *220.61 Feeder or Service Neutral Load.
> 
> (A) Basic Calculation. *The feeder or service neutral load
> shall be the maximum unbalance of the load determined by
> ...


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## Wireman191 (Aug 28, 2011)

rdr said:


> If anything seen it upsized where more than one circuit share it but never reduced. Logically, shouldn't be allowed. :blink:


 Why would it be up sized?:blink:
There is no way that the neutral will see more current then the ungrounded conductors.


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## LightsOn81 (Jan 6, 2012)

The man ain't asking to upsize; he want to know if it's ok to derate the neutral anywhere other than the service entrance


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## BBQ (Nov 16, 2010)

Wireman191 said:


> Why would it be up sized?:blink:
> There is no way that the neutral will see more current then the ungrounded conductors.


Engineers often specify up-sized neutrals, sometimes double the amperage of the circuit conductors if the feeder or multiwire branch circuit is supplying non-linear loads such as computers from 3 phase Wye systems.

Under certain conditions harmonic currents can add up on the neutral meaning it will carry more current than any one ungrounded conductor. Good design can eliminate the need for up-sized neutrals.


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## Wireman191 (Aug 28, 2011)

BBQ said:


> Engineers often specify up-sized neutrals, sometimes double the amperage of the circuit conductors if the feeder or multiwire branch circuit is supplying non-linear loads such as computers from 3 phase Wye systems.
> 
> Under certain conditions harmonic currents can add up on the neutral meaning it will carry more current than any one ungrounded conductor. Good design can eliminate the need for up-sized neutrals.


 So A phase has 60 amps, B phase has 3 amps, the neutral will see 57 amps..... How much will harmonics add to that? Remember a tiny tiny bit about harmonics in school.


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## Dennis Alwon (May 9, 2009)

Another article to look at is 215.2(A)(1)-- next to last paragraph.



> 215.2 Minimum Rating and Size.
> (A) Feeders Not More Than 600 Volts.
> (1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.
> Exception No. 1: Where the assembly, including the overcurrent devices protecting the feeder(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the feeder conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.
> ...


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## rdr (Oct 25, 2009)

Wireman191 said:


> Why would it be up sized?:blink:
> There is no way that the neutral will see more current then the ungrounded conductors.


I know that. 
You know that.
But when did engineers and logic ever go together?


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## Wireman191 (Aug 28, 2011)

rdr said:


> engineers and logic


 Two words not meant to be in the same sentence.:laughing:


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## chicken steve (Mar 22, 2011)

> (2) That portion consisting of nonlinear loads supplied
> from a 4-wire, wye-connected, 3-phase system


One would think that this , in _theory_, negates _any_ deduction....?

~CS~


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## HARRY304E (Sep 15, 2010)

HARRY304E said:


> NO it is not.


Wrong :no: read post 6 and 11 HARRY....:whistling2::laughing:


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## don_resqcapt19 (Jul 18, 2010)

Wireman191 said:


> So A phase has 60 amps, B phase has 3 amps, the neutral will see 57 amps..... How much will harmonics add to that? Remember a tiny tiny bit about harmonics in school.


That example appears to be a single phase circuit and harmonic currents do not add in the neutral of single phase systems.


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## Dennis Alwon (May 9, 2009)

> HARRY304E said:
> 
> 
> > NO it is not.
> ...


I love it when Harry argues with himself. :laughing:


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## Fibes (Feb 18, 2010)

Dennis Alwon said:


> I love it when Harry argues with himself. :laughing:


 The good thing is, it's always a polite argument.


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## oldtimer (Jun 10, 2010)

Fibes said:


> The good thing is, it's always a polite argument.


 AND..........Harry always wins the arguement!


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## Bulldog1 (Oct 21, 2011)

HARRY304E said:


> *NO it is not*.




Harry are you really an electrician? :blink:

Edit..... I posted this so you could argue it with yourself and let us know who wins...... :laughing:


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## HARRY304E (Sep 15, 2010)

Bulldog1 said:


> Harry are you really an electrician? :blink:
> 
> Edit..... I posted this so you could argue it with yourself and let us know who wins...... :laughing:


Well I have been losing the argument all morning maybe the afternoon will be better...:laughing:


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## Bulldog1 (Oct 21, 2011)

HARRY304E said:


> Well I have been losing the argument all morning maybe the afternoon will be better...:laughing:


If your lucky it will be.....:laughing:


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