# Derate Neutral



## Magnettica (Jan 23, 2007)

Derated neutral is good for oven ranges and electric dryers.

220.61 I believe.


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## Mr. Sparkle (Jan 27, 2009)

220.61 Also covers feeder neutral reduction:

FEEDER NEUTRAL LOAD
For 3-wire DC or single-phase AC, 4-wire, 3-phase, and 5-wire, 2-phase systems, a further demand factor of 70% shall be permitted for that portion of the unbalanced load in excess of 200 amperes. There shall be no reduction of neutral capacity for that portion of the load which consists of nonlinear loads such as electric-discharge lighting, data processing, or similar equipment (harmonics are present in these loads), and supplied from a 4-wire, wye-connected 3-phase system.

Example: What is the demand for a neutral load of 500 amperes?
Answer: 220.61 First 200 amps at 100% = 200 amps 
Remaining 300 amps x 70% = 210 amps
410 amps, neutral is reduced from 500 amps to 410.

So unless that sub is over 200A, which it isn't, I say no to derating.


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## Toronto Sparky (Apr 12, 2009)

I've seen neutrals de-rated in buildings that have significant 240v loads (baseboard heat or electric furnace ect.)


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## seo (Oct 28, 2008)

Per section 220.61 (A) you may be able to reduce your neutral. Also look at section 230.42 (C) and 250.24 (C) (1).


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## waco (Dec 10, 2007)

I'm confused.... 2-2-2-4 aluminum is pretty standard for a 100 amp feeder, although one jurisdiction allows it only with 90 amp OCP. I just did one using #1 aluminum because the inspector didn't want #2 used. The people at the supply house looked at me like I was crazy, but they had #1 SER.

I can't see derating the neutral at all for a feeder. If the load is pure 240, then treat it like a branch circuit and not a sub. Could it be the person was confused between a branch circuit disconnect and a sub-panel?


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## frenchelectrican (Mar 15, 2007)

John Valdes said:


> When can you derate a neutral. In particular sub panels. I have someone who pulled 2 #4's - 2 #6's for a 100 amp sub panel in an attached structure.
> 
> I told him he needed 3 #3's and 1 #8 for a 100 amp sub. But since he already pulled the feeder I told him he could use a 90 amp breaker. He has asked me if the #6 neutral will float. I am not sure. Any feedback appreciated.


 It might be ok if you only have 120/240 volt *single* phase with majorty of the load is 240 volts.

{ see more comment below }



Mr. Sparkle said:


> 220.61 Also covers feeder neutral reduction:
> 
> FEEDER NEUTRAL LOAD
> For 3-wire DC or single-phase AC, 4-wire, 3-phase, and 5-wire, 2-phase systems, a further demand factor of 70% shall be permitted for that portion of the unbalanced load in excess of 200 amperes. There shall be no reduction of neutral capacity for that portion of the load which consists of nonlinear loads such as electric-discharge lighting, data processing, or similar equipment (harmonics are present in these loads), and supplied from a 4-wire, wye-connected 3-phase system.
> ...


 It should be ok if only the single phase load have alot of 240 volts load and very little 120 volts { some local code may not allow that so watch out on that part }

Now if you get single phase *120/208* volts from three phase supply then no you can NOT use the reduced netural at all so just watch out on that part I know some peoples make a classic mistake if not watching the type of power source espcally if triphase or not.

Merci,Marc


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## John Valdes (May 17, 2007)

Thanks everyone. I told him to pull it all out and do it right. I told him the right way before he even started and then I find out he pulls the wrong size conductors. Thanks again....John


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## waco (Dec 10, 2007)

I'd like to re-visit this one since it looks to me like (talking copper) 4-4-6 would be adequate for a 100 amp feeder since the neutral can't exceed 50 amps (100 amps at 240 volts, 50 amps at 120 volts.)

So....


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## micromind (Aug 11, 2007)

I'm not completely sure, but I believe that the minimum neutral size is the same as the minimum ground size. I studied this once several years ago, it might have been a few code cycles ago. 

Sizing a neutral is more of an art than a science. As stated above, a full-size neutral is required is some cases, but not all.

Here's an example of how dumb a blanket full-size neutral can be. A few years ago, I did a pump station. It had an 800 amp 480 volt service, and a 600 KVA generator. The only load that involved the neutral was a 100 amp 480 volt panel. This panel fed the lights (1-20 amp circuit), some heat-trace (2-20 amp circuits), and a 30 KVA 3 phase transformer. 

The neutral was full-size. 2-500 MCM copper. 

Suppose that the neutral had been reduced to only one 500. Or even a 1/0. What would be the chances of overloading it in the next say, 300 years? 

If I design the installation, I usually reduce the neutral by one size. Unless there's a valid reason to make it full-size. 

As professional electricians, we need to look seriously at the installation as a whole. Certainly, we need to consider future possibilities, but to simply apply a blanket rule (that's not even required by code) is just not all that bright. 

I can't even count the number of times I've pulled two or three #3s and a #4 neutral. Even if the loads are all single pole. Look at how much the POCO reduces neutrals. I've certainly seen my share of open neutrals, but not one because of an overload.

Rob


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## waco (Dec 10, 2007)

Micromind's point is a good one, but #6 is the size of ground required for 100 amps, so it seems like a #6 neutral would be okay.


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