# Reduced Service Neutral



## Dennis Alwon (May 9, 2009)

You are missing art. 250.24(C)(1). If the calculated load permits you can go as small as your gec-- a #4 for 200 amps.


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## I_get_shocked (Apr 6, 2009)

Thanks for the reply. 

I see that it cant be smaller than the GEC and isn't required to be larger than the ungrounded. 

Now if you used the calculated reduced neutral, and your service is larger than 200A, would you then apply additional 70% reduction to the excess size past 200A?

250.24(c)(1)
(1) Sizing for a Single Raceway. The grounded conductor
shall not be smaller than the required grounding electrode
conductor specified in Table 250.66 but shall not be required
to be larger than the largest ungrounded serviceentrance
phase conductor(s). In addition, for sets of serviceentrance
phase conductors larger than 1100 kcmil copper or
1750 kcmil aluminum, the grounded conductor shall not be
smaller than 121⁄2 percent of the circular mil area of the
largest set of service-entrance phase conductor(s).


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## nitro71 (Sep 17, 2009)

In my area you get a carte blanche to put in 4/0 4/0 2/0 for residential 200 amp services.


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## Dennis Alwon (May 9, 2009)

I_get_shocked said:


> Thanks for the reply.
> 
> I see that it cant be smaller than the GEC and isn't required to be larger than the ungrounded.
> 
> Now if you used the calculated reduced neutral, and your service is larger than 200A, would you then apply additional 70% reduction to the excess size past 200A?



12.5% comes into play for service that have 1100 kcm conductors or larger

A 400 amp service can be as low as #2 or 1/0 depending on the install and everything else is still based on T.250.66 until your conductors are larger than 1100 kcm. Sorry if I am not understanding.


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## Shockdoc (Mar 4, 2010)

Good for all you guys.......LIPA here on Stupid island requires full size neutral for everything.


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## Dennis Alwon (May 9, 2009)

I see where you are going now, I think. 220.61 is the method which you can calculate the neutral load and 250.24(C) tells us the minimum. You want to know how to calculate for 400 amps service. 

I believe 220.61 says that any calculate load over 200 amps on the neutral can be decreased again by 70%. given that your install fits the (B)(1) & (2) description


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## Slider (Jun 3, 2008)

Dennis Alwon said:


> 12.5% comes into play for service that have 1100 kcm conductors or larger
> 
> A 400 amp service can be as low as #2 or 1/0 depending on the install and everything else is still based on T.250.66 until your conductors are larger than 1100 kcm. Sorry if I am not understanding.


 
I am doing a 320/400 amp service soon and the poco said to run 500mcm and 4/0 for the neutral. Is this common for a 320/400? I was just curious. Thanks


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## desar (Feb 6, 2011)

I beleive that you have to do a load Calc. and apply your 70% to electric cooking equipment and 70% of electric ranges. The 70% rule for a nuetral load over 200amps usually will only apply in multi family load calcs. When you calc a multi family you apply the first 70% rule for electric ranges and dryers all ther loads at 100% if they have nuetral ,then if your va in the nuetral at the end of the calc divided by voltage = over 200a then you apply another 70% . Don't forget the 12 1/2% rule also applies to the sizing of the main bonding jumper.


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## Dennis Alwon (May 9, 2009)

Slider said:


> I am doing a 320/400 amp service soon and the poco said to run 500mcm and 4/0 for the neutral. Is this common for a 320/400? I was just curious. Thanks


 Is this a residence? Are we talking copper or alum.? I assume you are running the underground to the meter--is there voltage drop involved.



desar said:


> Don't forget the 12 1/2% rule also applies to the sizing of the main bonding jumper.


I disagree T250.66 applies to the GEC and bonding jumpers.


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## Slider (Jun 3, 2008)

Yes it is a residence. Aluminum conductors underground from pole to meter at house about 150ft. I have yet to get my final plans / hvac / kitchen / so on info from the builder so I have not done an official load calculation. I am hoping to be able to use the 320 meter socket. Had a meeting with the poco on site and they asked us to use 500mcm and 4/0 neutral. Thank you for your help.


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## Dennis Alwon (May 9, 2009)

Slider said:


> Yes it is a residence. Aluminum conductors underground from pole to meter at house about 150ft. I have yet to get my final plans / hvac / kitchen / so on info from the builder so I have not done an official load calculation. I am hoping to be able to use the 320 meter socket. Had a meeting with the poco on site and they asked us to use 500mcm and 4/0 neutral. Thank you for your help.


I would think if this is your responsibility that you would have to follow the NEC. The size would depend on the calculated load.


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## desar (Feb 6, 2011)

250.66 applies to bonding jumpers ,which the main bonding jumper falls under along with the system bonding jumper for seperately derived systems. You use 250.66 because on the supply side of the service their is no overcurrent device so you base your size on the conductor size.Under services you must bond all metal enclosures and raceways.


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