Sizing Neutral or Grounded Conductor

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rwreuter

Senior Member
I have found an odd thing here in local area that electricians are telling me and again I am looking for some NEC guidance to support it.

In the past and from my experience it was acceptable in compliance to run 4/0-4/0-2/0 for service entrance conductors (using a 2/0 for the grounded conductor, or neutral).

For some reason people are stating that the local municipality doesn't want you to size the grounded conductor more than 80% different than the conductors. Which of course means that you can't use 2/0, the common SEC used in the local area is 4/0-4/0-4/0.

I ask, is this and can this be supported by the NEC or is it a local rule. FYI, I have read the local rules and have seen nothing in there that supports this.



rw
 

Dennis Alwon

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Location
Chapel Hill, NC
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Retired Electrical Contractor
There is nothing that can support what the inspector wants for those size service entrance conductors.. Look at art. 250.24(C). It may be as small as the GEC but you would need to calculated the neutral load.
 

infinity

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Location
New Jersey
Occupation
Journeyman Electrician
Do they really think that the unbalanced load on the neutral will exceed 135 amps? As Dennis pointed out a load calculation is needed to find the actual neutral load and the NEC does not support your local municipalities position.
 

rwreuter

Senior Member
There is nothing that can support what the inspector wants for those size service entrance conductors.. Look at art. 250.24(C). It may be as small as the GEC but you would need to calculated the neutral load.

aint that the truth dennis!!!!!

just curious if the NEC can support it....it seems as if every this crazy municipality challenges basic things I learned years ago and causes me to go digging.
 

rwreuter

Senior Member
Do they really think that the unbalanced load on the neutral will exceed 135 amps? As Dennis pointed out a load calculation is needed to find the actual neutral load and the NEC does not support your local municipalities position.

the unbalance load won't exceed 135 amps at all.


rw
 

Smart $

Esteemed Member
Location
Ohio
2/0 alum should not be an issue then.
...provided the "maximum unbalanced neutral current" was calculated correctly. (...and I have a sneaking suspicion that no calculation was done, but rather a surmising of such from experience coupled with the ampacity of the mentioned grounded conductor.)

Many seem to think this is just the unbalanced neutral current with everything turned on. It is not. As a matter of fact it is determined, in essence, by turning half or more of the loads off.
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
...provided the "maximum unbalanced neutral current" was calculated correctly. (...and I have a sneaking suspicion that no calculation was done, but rather a surmising of such from experience coupled with the ampacity of the mentioned grounded conductor.)


That may or may not be true but the real issue here is the local requirement that the neutral not be less than 80% in size when compared to the ungrounded conductors. This isn't supported by the NEC so it's anyone's guess as to why they choose to enforce this 80% rule. 4/0-4/0-2/0 for 200 amp service entrance conductors is the norm just about everywhere that allows SE cable. In general should we assume that it's unsafe?
 

rwreuter

Senior Member
That may or may not be true but the real issue here is the local requirement that the neutral not be less than 80% in size when compared to the ungrounded conductors. This isn't supported by the NEC so it's anyone's guess as to why they choose to enforce this 80% rule. 4/0-4/0-2/0 for 200 amp service entrance conductors is the norm just about everywhere that allows SE cable. In general should we assume that it's unsafe?

I like your thought process.....just wanted to know if something changed that I hadn't been aware of. You know, like a meteor hitting my house and me not noticing. LOL
 

Smart $

Esteemed Member
Location
Ohio
That may or may not be true but the real issue here is the local requirement that the neutral not be less than 80% in size when compared to the ungrounded conductors. This isn't supported by the NEC so it's anyone's guess as to why they choose to enforce this 80% rule. 4/0-4/0-2/0 for 200 amp service entrance conductors is the norm just about everywhere that allows SE cable. In general should we assume that it's unsafe?
I believe, by mere speculation, that is the point the municipalty is going on. We should not assume either way, and I believe the municipality has found more cases that assume it to be safe than not. Do not take my comments as neither condoning nor disapproving of the municipality's position.

In Ohio, a municipality cannot make such a local requirement without the approval of the State.
 
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infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I believe, by mere speculation, that is the point the municipalty is going on. We should not assume in this regard, and I believe the municipality has found more cases than not that do. Do not take my comments as neither condoning nor disapproving of the municipality's position.


Yeah, we all seem to agree that we just don't know what their thinking is. I'm only commenting that the NEC is a national standard and IMO if the reduced neutral in SE cable were a problem no of us would be permitted to use it. If you look at a typical 200 amp service in a dwelling I'm not seeing how you could ever overload a neutral that has an ampacity of 135 amps.
 

rwreuter

Senior Member
I agree, usually most residential home won't even use 135amp on both phases combined. This home in question won't, propane is operating the furnace and more than likely the range.


rw
 

Smart $

Esteemed Member
Location
Ohio
... If you look at a typical 200 amp service in a dwelling I'm not seeing how you could ever overload a neutral that has an ampacity of 135 amps.

I agree, usually most residential home won't even use 135amp on both phases combined. ...
Perhaps true... but you are both arguing with a premise that is likely at the very root of enacting the local requirement. It is not an assumption to be made... if so, show it to me in the NEC.

IMO, the proper course of action for the municipality would be to enforce documenting of calculations and verification of such, or at the very least, provide for such as an out to the requirement. They appear to be taking the lazy way out.
 

rwreuter

Senior Member
interesting......something else here, what was the reason that the instituted that requirement? what was the cause? there is no way i can see a load on a 200amp service ever being able to become that unbalanced....


even if you tried i don't think you could screw it up that bad.
 

Smart $

Esteemed Member
Location
Ohio
interesting......something else here, what was the reason that the instituted that requirement? what was the cause? there is no way i can see a load on a 200amp service ever being able to become that unbalanced....


even if you tried i don't think you could screw it up that bad.
Odds are you are correct... but its the one "even" that proves the odds wrong.

Taking only the odds into consideration is not the prescribed NEC method for the proper [minimum] sizing of the neutral conductor, no matter which way you try to step around it.
 

rwreuter

Senior Member
Odds are you are correct... but its the one "even" that proves the odds wrong.

Taking only the odds into consideration is not the prescribed NEC method for the proper [minimum] sizing of the neutral conductor, no matter which way you try to step around it.



LOL

Article 100----Odds--take into consideration all possible scenerios and choose the one that makes most sense in the situation.
 
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