# Sizing neutral in parallel service



## Family guy (May 15, 2016)

We are installing a 2000 amp service and we are running 6 sets of 500 kcmil for each phase. The way it is set up it is to be phase A plus a neutral in one phase B plus neutral in another and phase C plus neutral in the final one. It is outside underground pvc raceway. The neutral I have figured out to be 2/0 to be sufficient at 12.5% of the ungrounded phases. We are going try make it the same length, same characteristics and same termination. Does anyone here see why this would violate code. I know it seems better practice maybe to have a fourth raceway to run neutrals, but it is a hard change at this point. Thank you for your input.


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## wildleg (Apr 12, 2009)

did not understand how you are running the conductors. you mentioned 3 phase conductors and 3 neutrals.

how close are the pipes.

what you suggest is allowed, but it's scary to me. the dangerous part is entering the cabinet at the termination.



> 2011
> 
> 300.3 Conductors.
> (A) Single Conductors. Single conductors specified in
> ...


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## Family guy (May 15, 2016)

Sorry 3 conduits total of 7 wires in each. 6- 500 kcmil as Phase A plus 2/0 neutral, 6- 500 kcmil as Phase B plus 2/0 neutral, 6-500 kcmil as phase C plus 2/0 neutral


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## Switched (Dec 23, 2012)

Family guy said:


> We are installing a 2000 amp service and we are running 6 sets of 500 kcmil for each phase. The way it is set up it is to be phase A plus a neutral in one phase B plus neutral in another and phase C plus neutral in the final one. It is outside underground pvc raceway. The neutral I have figured out to be 2/0 to be sufficient at 12.5% of the ungrounded phases. We are going try make it the same length, same characteristics and same termination. Does anyone here see why this would violate code. *I know it seems better practice maybe to have a fourth raceway to run neutrals, but it is a hard change at this point*. Thank you for your input.
> 
> 
> Sent from my iPhone using Tapatalk


Are you saying you would normally run the neutrals in a separate conduit? You lost me there.

As far as derating the Neutral, I don't see why you can't do that if that is what the calculations prove. But there are much wiser code save minds here....


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## joebanana (Dec 21, 2010)

Table 250.102 (c) (1) says 1/0, so 2/0 should be good. You know you need all 3 phases + the neuch in each conduit, right?


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## Family guy (May 15, 2016)

We are using exception in 300.3(b)(1) where we are underground and isolating each phase in their own conduit. In the back of my mind there is question that maybe the neutral needs to be full sized and that would be 400 kcmil. I am not sure where this idea comes from as I do not verify it by code.
I also was reading article and they brought out that a 3 phase system done this way would have 4 raceways. One for each phase and then one for the neutral.


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## Switched (Dec 23, 2012)

Family guy said:


> We are using exception in 300.3(b)(1) where we are underground and isolating each phase in their own conduit. In the back of my mind there is question that maybe the neutral needs to be full sized and that would be 400 kcmil. I am not sure where this idea comes from as I do not verify it by code.
> *I also was reading article and they brought out that a 3 phase system done this way would have 4 raceways. One for each phase and then one for the neutral.*
> 
> 
> Sent from my iPhone using Tapatalk


Where did you read that? I was under the assumption that you needed to group the conductors to prevent inductive heating. 

300.3(B)(1) is letting you know that the you need all the circuit conductors within the same raceway. So AFAIK, having 4 separate conduits with each phase in a separate conduit would be a violation and create an issue.

No?


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## Family guy (May 15, 2016)

That is where the exception comes in. If in nonmetallic raceway and underground it is permitted to arranged as isolated phase, neutral , and grounded conductor installations. Their are rules that apply in going into metal enclosures and such. 
I read this in the electrical contractors magazine where they mentioned the 4th conduit.


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## frenchelectrican (Mar 15, 2007)

To familyguy .,

How big the conduit you are planning to use ?

Is the set up you are plan to run to single 2000 amp main OCPD or what ?

And this will be all in PVC conduit ? 

I know it can be done as I have see it before but IMO it is not the best option but it do work as long there is no metallic conduit.


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## Switched (Dec 23, 2012)

Gotcha... missed that for some reason.

300.5(I) Ex2 covers this


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## frenchelectrican (Mar 15, 2007)

Switched said:


> Gotcha... missed that for some reason.
> 
> 300.5(I) Ex2 covers this


The only spot it may bite ya is the sweeps if you are coming up from underground run. I know some are tempting to use steel sweep but to order stay on 300.5(1) Ex 2 it have to be all PVC nothing metal along the route.


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## Family guy (May 15, 2016)

I am actually just helping in this job and I believe it is 4 inch pvc. That is ran. It is a 2000 amp main that is being fed. From there it serves other load centers and a transformer which supplies 120/240 volt power. The boss man asked my opinion on this today. I am working with him on a part time basis so I am not there for sections of the job. I want to make sure I am not leading him astray if I can help it.


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## Family guy (May 15, 2016)

Yes definitely all pvc raceway.


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## Cow (Jan 16, 2008)

We do 2000 amp services fairly regularly.


Standard procedure for us is six 4" conduits, with ABCN in each.



400mcm phases
1/0 neutrals unless we have some real neutral load. Or an engineer that's covering his @ss. Six 1/0's is still 900 amps worth of wire. Pretty tough to hit 900 amps of neutral load on a 2000 amp service.


4" because I like easy wire pulls even when using a tugger.


So I'm curious how you are cramming all this into three conduits with derating probably coming into play?



What size are your conduits? How long are they?


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## varmit (Apr 19, 2009)

Your wire size is off for the phases. 
500 kcmil copper @ 75 C = 380 A (x .8 derate) = 304 A x 6 = 1824 amps
500 kcmil alum 275 C = 310 A (x.8 derate) = 248 A x 6 = 1488 amps

At a service rating above 800 amps, you can not "round up" a size on over current protection.

You will need more conduit and larger wire.


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## Family guy (May 15, 2016)

I was thinking that when derating we are allowed to use the 90 degree column. 


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## Family guy (May 15, 2016)

I was thinking that we can use the 90 degree column when derating


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## varmit (Apr 19, 2009)

My suggestion would be (6) runs of 4 inch PVC each with (3) 600 kcmil aluminum and a 3/0 neutral in an ABC + N configuration. This would have an ampacity rating of 2040 amps.


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## Family guy (May 15, 2016)

Yes I agree that is ideal situation. This is kind of at where we are at now.
Curious though when trenching then in you would go deep and stack two and go three across to keep wire lengths similar?


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## frenchelectrican (Mar 15, 2007)

Family guy said:


> I am actually just helping in this job and I believe it is 4 inch pvc. That is ran. It is a 2000 amp main that is being fed. From there it serves other load centers and a transformer which supplies 120/240 volt power. The boss man asked my opinion on this today. I am working with him on a part time basis so I am not there for sections of the job. I want to make sure I am not leading him astray if I can help it.
> 
> 
> Sent from my iPhone using Tapatalk


That can be little sticky there due you have 2000 amp main switch unforetally you will have to sized it to meet the OCPD rating as Cow and couple other members posted what they typically done .

I run almost excat same way with Cow with conductors and conduit set up I rather run at least 6 conduits plus a spare one along the way especially with underground run. ( you will be surprised what the POCO may ask ya to put in a spare one in ) 

I useally run 500 Cu or 600 Al depending on the distance and yes of course 6 conduit in 4 inch size with wide sweeps coming up.

Family guy ., Typically I run the conduits in 3 wide and 2 up is my typical runs unless you have wide flat trench then all flat.


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## Dennis Alwon (May 9, 2009)

The exceptions allows each phase to be run in the conduit as long as the conduit is nonmetallic and outside. The only issue I see is the code does not specifically state the neutral can be in the same conduit with each phase but I don't think that is an issue.


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## Family guy (May 15, 2016)

Just heard back from the guys today and they decided to put neutral in a separate conduit. I was glad to hear that. Thanks everyone.


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