# Multiwire Branch Circuits



## HARRY304E (Sep 15, 2010)

mud99 said:


> I am having an argument with our electrician, and I was hoping that someone could answer whether this wiring arrangement is allowed under any circumstances, perhaps with a code reference.
> 
> Our electrician has run a multiwire branch circuit in EMT consisting of three #12 hot wires and one #12 neutral. The service is split phase. Each of the hots is on a 20 amp breaker, on phases A,B,A.
> 
> My opinion is that we need to run a second neutral, or size the neutral to wire rated for 40amps.



What do you meen by The service is split phase?:blink:


Welcome to the forum..:thumbup:


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## mud99 (Dec 2, 2010)

Split Phase = "*3-wire, single-phase, mid-point neutral*"
http://en.wikipedia.org/wiki/Split-phase_electric_power

Thanks, I've been spying on the discussions here for a while, trying to learn as much as I can, I guess this is my first post 



HARRY304E said:


> What do you meen by The service is split phase?:blink:
> 
> 
> Welcome to the forum..:thumbup:


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## 480sparky (Sep 20, 2007)

If the service is three phase, then it's a legal and accepted method.

If it's single-phase, then another noodle is needed.


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## RobTownfold64 (Mar 17, 2011)

This is where I am confused:


> Each of the hots is on a 20 amp breaker, on phases A,B,A


 You would need to be on A, B, and C. 

ETA: I see you now said it's single phase.
Since you are speaking of single phase, you would need a second neutral.


Also


> or size the neutral to wire rated for 40amps.


 Not sure your code cycle, but in 2011 you won't be able to do that anymore.


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## mud99 (Dec 2, 2010)

Thank you sparky


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## HARRY304E (Sep 15, 2010)

mud99 said:


> Split Phase = "*3-wire, single-phase, mid-point neutral*"
> http://en.wikipedia.org/wiki/Split-phase_electric_power
> 
> Thanks, I've been spying on the discussions here for a while, trying to learn as much as I can, I guess this is my first post


Then i would say you need two neutrals..

You spy...:laughing:


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## mud99 (Dec 2, 2010)

Rob, it's single phase, not 3 phase.


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## raider1 (Jan 22, 2007)

mud99 said:


> I am having an argument with our electrician, and I was hoping that someone could answer whether this wiring arrangement is allowed under any circumstances, perhaps with a code reference.
> 
> Our electrician has run a multiwire branch circuit in EMT consisting of three #12 hot wires and one #12 neutral. The service is split phase. Each of the hots is on a 20 amp breaker, on phases A,B,A.


A single phase source with the arrangement that you have (A,B,A on a single neutral) is not defined as a multiwire branch circuit because you don't have a voltage between the 2 "A" phases. Therefore what is installed will overload the #12 neutral so a second neutral is required.



> My opinion is that we need to run a second neutral, or size the neutral to wire rated for 40amps.


The 2011 NEC specifically prohibits installing a larger neutral for the avobe situation. See 200.4.

So you will need to pull a second neutral for the second "A" circuit.

Chris


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## backstay (Feb 3, 2011)

The neutral has to be sized to carry the unbalanced load. 

If you look in Article 100 "a branch circuit that consists of two or more ungrounded conductors that have volatage between them..." two of your conductors do not have voltage between them. 

Art 210.4 NEC 2011 is about MWBC


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## knowshorts (Jan 9, 2009)

Yes you would need a 2nd neutral. 

CA is on the 2010 code (2008 NEC)

If the permit was pulled prior to 1/1/11, then it would fall under the 2007 code (2005 NEC)

For some reason I am thinking a permit was not pulled.

Watch out, this CL electrician may be using that EMT as a return path.


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## Shockdoc (Mar 4, 2010)

Unless he ran a #8 neutral he would need a second #12 .


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## TOOL_5150 (Aug 27, 2007)

Im going to go with: "You need a second noodle"

~Matt


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## mud99 (Dec 2, 2010)

As an update to this, the old electrician has been fired, and a new (licensed) electrician has been hired.

My conversation with the new electrician involved pointing at the panel and saying "i'm assuming you know what's wrong with this." at which point he just nodded his head.

Problems included improper torquing of everything, not twisting the wires in wire nuts, missing box covers, loose EMT fittings, swapped hots and neutrals at outlets, and the problem mentioned above.

The annoying part about this is that while I was standing around watching the old electrician, he actually did things properly - I assume that this was just a show. 

Thumbs up for licensed electricians.


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## Bkessler (Feb 14, 2007)

mud99 said:


> As an update to this, the old electrician has been fired, and a new (licensed) electrician has been hired.
> 
> My conversation with the new electrician involved pointing at the panel and saying "i'm assuming you know what's wrong with this." at which point he just nodded his head.
> 
> ...


And thumbs down if you originally hired an unlicensed electrician. Remember, if you hire an unlicensed electrician and he burns your building down. Your the one that is liable.


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## mud99 (Dec 2, 2010)

You may be right, but unless you are a licensed lawyer I would not give legal advice 

And he was hired by our licensed general contractor, so go figure...


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## knowshorts (Jan 9, 2009)

But, in order to get a contractors license, you must pass a test which is 50% law. Then there are additional laws we must study depending on how and where we conduct business. Ignorance of the law will not fly with us and it will not fly with you. If you hire someone, it is your responsibility to know everything about them and who they hire. This information should be given to you without question and if there's resistance, that should be a big red flag.


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## BBQ (Nov 16, 2010)

Bkessler said:


> And thumbs down if you originally hired an unlicensed electrician. Remember, if you hire an unlicensed electrician and he burns your building down. Your the one that is liable.


What????:blink::blink:


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## RobTownfold64 (Mar 17, 2011)

mud99 said:


> not twisting the wires in wire nuts


Don't say that, it'll start up another war!


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

RobTownfold64 said:


> Don't say that, it'll start up another war!


 

True , and not really a violation if the wirenut does not require it:thumbsup:


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## electricalwiz (Mar 12, 2011)

mcclary's electrical said:


> True , and not really a violation if the wirenut does not require it:thumbsup:



true, but a bad habit


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## kaboler (Dec 1, 2010)

If A and B, the first 2 hots, were going to a balanced load, or a proveable equal load, why would you need 2 neutrals? Especially if the first AB came from a 2pole breaker.


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## brian john (Mar 11, 2007)

HARRY304E said:


> What do you meen by The service is split phase?:blink:
> :



Split Phase is sometimes to describe 120/240 single phase.


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## Greg Glasgow (Dec 7, 2012)

mud99 said:


> I am having an argument with our electrician, and I was hoping that someone could answer whether this wiring arrangement is allowed under any circumstances, perhaps with a code reference.
> 
> Our electrician has run a multiwire branch circuit in EMT consisting of three #12 hot wires and one #12 neutral. The service is split phase. Each of the hots is on a 20 amp breaker, on phases A,B,A.
> 
> My opinion is that we need to run a second neutral, or size the neutral to wire rated for 40amps.


Sounds like your electrician is wiring for three phase. You're right, you need another neutral and also a 2pole breaker for your AB circuit.


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## Greg Glasgow (Dec 7, 2012)

kaboler said:


> If A and B, the first 2 hots, were going to a balanced load, or a proveable equal load, why would you need 2 neutrals? Especially if the first AB came from a 2pole breaker.


If the AB circuit was for a designated load, such as elec heat, no neutral is required, but that was not specified in the original question.


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## 480sparky (Sep 20, 2007)

What is your electrical related field/trade:
.

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