# Reduced neutral on Wye system



## frenchelectrican (Mar 15, 2007)

Southeast Power said:


> We are looking at installing an ATS and generator for a 120/208 volt 2000amp service.
> The survey shows 6 sets of 3- 500 copper and 1- 250 in 4” PVC.
> 
> The building was built in 1994 in Miami-Dade county.
> ...


I am not sure but maybe the EE may spec'ed that due the line to neutral load is not very high so that is one possibility. 

Ask for RFI for details on that.


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## Bird dog (Oct 27, 2015)

IIRC if there are no neutral loads, the service neutral has to be sized at least the same size as your service bonding conductor according to T250.66 to handle fault current.


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## Cow (Jan 16, 2008)

We do lots of 480/277v wye services.

My last 2000 amp I designed had 6 sets of 400mcm CU with a 1/0 CU neutral.

1/0=150 amp x 6 sets=900 amp neutral capacity. That'd be a lot of neutral load to hit 900 amps on a 2000 amp service.

Most of our service loads are typically 3 phase for the most part, with a little 277v lighting mixed in.


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## dronai (Apr 11, 2011)

The last run I did, that had parallel conductors was in a gutter. When you guys do 6 sets like that, are you in (6) separate conduits ?


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## Southeast Power (Jan 18, 2009)

This is what we have from the utility feeding the main:









These are the neutrals:


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## Cow (Jan 16, 2008)

dronai said:


> The last run I did, that had parallel conductors was in a gutter. When you guys do 6 sets like that, are you in (6) separate conduits ?


We do separate conduits.


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## dronai (Apr 11, 2011)

You guys use these ?


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## frenchelectrican (Mar 15, 2007)

dronai said:


> You guys use these ?


I do use them from time to time depending on conductor size and layout it is.,,

But only one quirk is that ya need a greenhorn grunt to help ya to hold it or run the hand pump.

The other thing is pay attention to die setting on them they can get pretty finky if not carefull espcally if you squeeze the alum conductors .,,


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## frenchelectrican (Mar 15, 2007)

Bird dog said:


> IIRC if there are no neutral loads, the service neutral has to be sized at least the same size as your service bonding conductor according to T250.66 to handle fault current.


Yuh but I recall they did mention 12% if you are running large sets of conductors that what I know it was kinda a general thumb of rules but 15% is norm on large system.

But yes you are on something like that.


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## telsa (May 22, 2015)

At that size, C-10s are not allowed to make the call. 

It gets tossed to EEs every time.

Obviously, three-phase loads can be backed out. 

But in Commercial work, there is never all that much 3-phase.

Lighting and other 1-phase loads overwhelm the power-flow.

Industrial is a totally different animal. There 1-phase loads are a joke... usually


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## CoolWill (Jan 5, 2019)

Reduced neutrals will be in 215, 220, and 230. At any rate, the neutral is sized to carry the maximum unbalanced load, so you have to do the calculations if you want to reduce. This being for Wye of course.

High leg deltas have to have a full sized neutral.


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## Cow (Jan 16, 2008)

dronai said:


> You guys use these ?


No.

The gear we buy and the way we lay the conduits out help facilitate wire installation without resorting to mechanical means to bend the conductors.


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## kb1jb1 (Nov 11, 2017)

Be careful if you have non linear loads and harmonics. If so then you will need a full size neutral. The neutral could carry the same current as a phase conductor.. If there are a lot of VFDs, electronic ballasts, computers.... etc.


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## oliquir (Jan 13, 2011)

even if all loads are 1 phase, the current on the neutral from the gen or xfmer will be almost zero if loads are distributed equally


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## telsa (May 22, 2015)

oliquir said:


> even if all loads are 1 phase, the current on the neutral from the gen or xfmer will be almost zero if loads are distributed equally


Absolutely true -- but you can't build to the ideal, balanced, situation.

The REVERSE is true. You design to the worst possible imbalance -- like if a fuse blew and the joint started single phasing, etc. 

:vs_OMG:


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## Southeast Power (Jan 18, 2009)

CoolWill said:


> Reduced neutrals will be in 215, 220, and 230. At any rate, the neutral is sized to carry the maximum unbalanced load, so you have to do the calculations if you want to reduce. This being for Wye of course.
> 
> High leg deltas have to have a full sized neutral.


No.
We always reduce the high leg neutral.


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## Southeast Power (Jan 18, 2009)

telsa said:


> At that size, C-10s are not allowed to make the call.
> 
> It gets tossed to EEs every time.
> 
> ...


Most of our 3 phase loads are mechanical systems

The lighting is usually 1/3.


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## CoolWill (Jan 5, 2019)

Southeast Power said:


> No.
> We always reduce the high leg neutral.


You're right. I glanced the code and saw delta, but it was talking about corner grounded systems.


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## micromind (Aug 11, 2007)

The PUCO around here always reduces the neutral. Often, our neutral is larger than theirs and neither one burns up. 

Makes ya wonder sometimes......


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