# neutral size rule



## RICK BOYD (Mar 10, 2008)

Where in the code do I justify the size of the neutral being smaller than the hots in a service
I know why I just can't find the rule


Rick


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## raider1 (Jan 22, 2007)

Take a look at 230.42(C) and 220.61.

Chris


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## Dennis Alwon (May 9, 2009)

How about 250.24(C)(1)


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## raider1 (Jan 22, 2007)

Dennis Alwon said:


> How about 250.24(C)(1)


That section is referenced by 230.42.

Chris


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## NolaTigaBait (Oct 19, 2008)

Does anyone even use this rule?...I always just wire the neutral the same size as the ungrounded conductors. I guess on a huge commercial job with thousands of feet of wire maybe?


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## MDShunk (Jan 7, 2007)

NolaTigaBait said:


> Does anyone even use this rule?...I always just wire the neutral the same size as the ungrounded conductors. I guess on a huge commercial job with thousands of feet of wire maybe?


I have the option of buying SEU with the smaller neutral. I often do.


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## NolaTigaBait (Oct 19, 2008)

MDShunk said:


> I have the option of buying SEU with the smaller neutral. I often do.


I wasn't aware they made it that way. What's the cost difference?


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## MDShunk (Jan 7, 2007)

NolaTigaBait said:


> I wasn't aware they made it that way. What's the cost difference?


about a nickel a foot.


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## NolaTigaBait (Oct 19, 2008)

Serious?...That isn't much of a savings.


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## MDShunk (Jan 7, 2007)

NolaTigaBait said:


> Serious?...That isn't much of a savings.


If you have to carry the roll of it from the store to the truck, you might appreciate the savings in an entirely new way.


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## NolaTigaBait (Oct 19, 2008)

MDShunk said:


> If you have to carry the roll of it from the store to the truck, you might appreciate the savings in an entirely new way.


Good point. I had to run a 70 feet of 4/0 ser feeder in a fishing camp 16 feet off the ground the other day. A few less pounds would have been nice.


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## Dennis Alwon (May 9, 2009)

I often install 400 amp services with 2- 200amp panels outdoors that have feed thru lugs. I then pipe to the inside panels sometimes 50- 75 feet away with 3/0 copper and a 1/0 grounded conductor. 

If the calculated load was small enough I could actually go down to a #2 in each panel but I never have done that.


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## RePhase277 (Feb 5, 2008)

Often times the neutral size is a spec'd size. Seems like most of the jobs I do spec full size neutrals.


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## Dennis Alwon (May 9, 2009)

InPhase277 said:


> Often times the neutral size is a spec'd size. Seems like most of the jobs I do spec full size neutrals.


I don't doubt it but I bet you do commercial work and not resi work where the neutral is spec'd.


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## RICK BOYD (Mar 10, 2008)

*wire price diff*



NolaTigaBait said:


> Does anyone even use this rule?...I always just wire the neutral the same size as the ungrounded conductors. I guess on a huge commercial job with thousands of feet of wire maybe?


I went to get feeders for 200amp panel 
3/0 3/0 1/0 copper was $9.00 a foot x 20' = $180.00
4/0 4/0 2/0 al was 2.50 a foot x 20'= $ 50.00
the 4/0 4/0 2/0 was on the roll already together
and of course I'm comparing copper to al price not 3/0 vs 1/0 price
Rick


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## RICK BOYD (Mar 10, 2008)

so what size ground do you use on those?
I am doing one like that now

this in ref to Dennis and his 400 amp service feeding two panels


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## Dennis Alwon (May 9, 2009)

RICK BOYD said:


> so what size ground do you use on those?
> I am doing one like that now
> 
> this in ref to Dennis and his 400 amp service feeding two panels


Your EGC is determined by 250.122 and what size OCPD you have. In my case a #6 is all that is needed to each panel, but I often pull #4 simply because I stock that size.


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## goose134 (Nov 12, 2007)

Doing a job for a hospital now and each MRI room calls for one ground and an isolated ground, each to be the same size as hots. For what it's worth, in Chicago neutral must be same size as ungrounded conductors in services up to 400 amps.


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## Loose Neutral (Jun 3, 2009)

I've been on jobs where they oversize the neutral and call it a super neutral.


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## Toronto Sparky (Apr 12, 2009)

I've seen a lot of jobs lately that they spec a larger (or even doubled up) neutral for feeders.


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## electures (Oct 23, 2008)

*See 310.15(B)(6)*



RICK BOYD said:


> Where in the code do I justify the size of the neutral being smaller than the hots in a service
> I know why I just can't find the rule
> 
> Rick


It can be found in 310.15(B)(6) last sentence. *The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.*

Please note that this can only be used on 120/240-volt, 3-wire, single-phase *dwelling services and feeders. *This is why I will only accept SE and SER cable for non-dwelling services if the contractor provides the calculations for the grounded and ungrounded conductors. 2/0 SE/SER cable has a 1/0 grounded conductor. 2/0AL is rated 135A. 1/0 AL is rated at 120A. 4/0 SE/SER cable has a 2/0 grounded conductor. 2/0 is rated at 135A. 4/0 SE/SER cable can only be used on non-dwelling 200A services and feeders if the calculated load does not exceed 180A on the ungrounded conductors and 135A on the grounded conductor.

The only way to undersize the neutral is if the calculated load is provided, *otherwise fullsize*. If there is no neutral load, then the grounded service conductor is the same size as the GEC per 250.24(C) (1) and 250.66. When the table max is reached then the grounded service conductor increases to 12.5% of the ungrounded conductors.

Hope this helps!:thumbsup:


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## McClary’s Electrical (Feb 21, 2009)

electures said:


> It can be found in 310.15(B)(6) last sentence. *The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.*
> 
> Please note that this can only be used on 120/240-volt, 3-wire, single-phase *dwelling services and feeders. *This is why I will only accept SE and SER cable for non-dwelling services if the contractor provides the calculations for the grounded and ungrounded conductors. 2/0 SE/SER cable has a 1/0 grounded conductor. 2/0AL is rated 135A. 1/0 AL is rated at 120A. 4/0 SE/SER cable has a 2/0 grounded conductor. 2/0 is rated at 135A. 4/0 SE/SER cable can only be used on non-dwelling 200A services and feeders if the calculated load does not exceed 180A on the ungrounded conductors and 135A on the grounded conductor.
> 
> ...


 
4/0 SE/ SER cannot be used for a non dwelling 200 amp. 310.16 must be used.


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## electures (Oct 23, 2008)

*Yes it can.., If the calculated load does not exceed 180 amperes.*



mcclary's electrical said:


> 4/0 SE/ SER cannot be used for a non dwelling 200 amp. 310.16 must be used.


230.42(A) General. The ampacity of the service-entrance conductors before the application of any adjustment or correction factors shall not be less than either (A)(1) or (A)(2). Loads shall be determined in accordance with Part III. IV, or V of article 220, as applicable. Ampacity shall be determined from 310.15. The maximum allowable current of busways shall be that value for which the busawy has been listed or labeled.

(1) The sum of the noncontinuous loads plus 125% of the continuous loads.

(2) The sum of the noncontinuous loads plus the continuous load if the service-entrance conductors terminate in an overcurrent device where both the overcurrent devcie and its assembly are listed for operation at 100% of their rating.

230.79. Rating of Service Disconnecting Means. The sevice disconnecting means shall have a rating not less that the *calculated load* to be carried, determined in accordance with Part III, IV, or V of Article 220, as applicable.

240.4(B) Devices rated 800 Amperes or Less. The next higher standard overcurrent device rating *(above the ampacity of the conductors being protected)* shall be permitted to be used, provided all of the following conditions are met:

(1) The conductors protected are not part of a multioutlet branch circuit...,

(2) *The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjuctments above its rating (but that shall be permitted to have other trip or rating adjustments).*

(3) The next higher standard rating selected does not exceed 800 amperes.

If you disagree with this, please provide the code section(s)...

:no:


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## McClary’s Electrical (Feb 21, 2009)

electures said:


> 230.42(A) General. The ampacity of the service-entrance conductors before the application of any adjustment or correction factors shall not be less than either (A)(1) or (A)(2). Loads shall be determined in accordance with Part III. IV, or V of article 220, as applicable. Ampacity shall be determined from 310.15. The maximum allowable current of busways shall be that value for which the busawy has been listed or labeled.
> 
> (1) The sum of the noncontinuous loads plus 125% of the continuous loads.
> 
> ...


 
I agree, But when I said a 200,,I meant a true 200


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## BuzzKill (Oct 27, 2008)

Toronto Sparky said:


> I've seen a lot of jobs lately that they spec a larger (or even doubled up) neutral for feeders.


 Guess that's a harmonics thing.


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