# Same phase sharing neutral



## RePhase277

You have pretty much nailed it. Except for the voltage on the neutral. If two circuits on the same phase share a neutral, the current in the neutral will add. The voltage across the neutral is still zero, or very close.

I don't know about Canada, but the NEC does allow this if the neutral is sized appropriately. However, I have never seen anyone do this, and would never do it myself.


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## JustDave

Awesome! Thanks for the prompt reply.

Well, hearing my assumptions are almost all correct is a good thing :laughing: I just want to work out a few more things though if you don't mind!

The voltage across the neutral is still zero... hmm. By this do you mean that the change in voltage is zero/minimal? Or do you quite literally mean, the measure of voltage on the neutral is zero, due to voltage drop at the load?

Also to clear up my earlier question: What would happen if two of the same phase was to share the same neutral.

A. Blow up at the neutral splices?
B. Trip the breaker?

Looking forward to see what you have to say 

Wow, so the NEC would allow this... interesting. So theoretically, one could return two live wires of the same phase so long as the neutral was of sufficient size.

Thanks again :thumbsup:


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## RePhase277

The voltage on the neutral is very close to zero because it s connected to ground at the service equipment. When a current flows, that changes slightly, but not enough to be significant.

An overloaded neutral would simply overheat if it wasn't sized properly. This would be especially evident at splices. I have seen wire nuts melted from this very thing. Nothing as dramatic as an explosion. And no breakers would trip unless the hot wire feeding the circuit was overloaded.

And while the NEC allows it, it is more or less a hold over from days gone by. We now require that circuits that share a neutral to be disconnected simultaneously, but with the way panels are laid out, it would be hard to connect the handles of breakers together that are on the same phase.


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## JustDave

Thanks alot, very informative :thumbsup: You have answered all of my questions.


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## Dennis Alwon

InPhase277 said:


> I don't know about Canada, but the NEC does allow this if the neutral is sized appropriately. However, I have never seen anyone do this, and would never do it myself.


I might disagree with this only in practical sense. The NEC 2008 now requires simultaneously disconnecting all ungrounded circuits of a MWBC. Art. 210.4.

Technically this would not be considered a MWBC but I would think the effect would be the same. I wonder if the 2011 would have an amendment to this.


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## MDShunk

When you open a panel and see a neutral that is remarkably brown in color, that's your clue that it might be a multiwire branch circuit that someone fed both hots with the same leg.


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## 480sparky

Two circuits on the same phase sharing a neutral is permitted by the NEC, AFAIK, but I've never heard of it done.


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## Greg

My take on this scenario is, if the "neutral" is shard by 2 hots on the same phase or leg, it is technically a grounded conductor. The voltage seen on the grounded conductor is still 120vac only the current is additive. Thus meaning 15A and 15A on L1 or "A" phase is 30A, which would mean you would need a grounded conductor capable of handling 30A. It is only considered a "neutral" on a MWBC and then it only carries the unbalanced portion of the load.


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## RePhase277

Greg said:


> My take on this scenario is, if the "neutral" is shard by 2 hots on the same phase or leg, it is technically a grounded conductor. The voltage seen on the grounded conductor is still 120vac only the current is additive. Thus meaning 15A and 15A on L1 or "A" phase is 30A, which would mean you would need a grounded conductor capable of handling 30A. It is only considered a "neutral" on a MWBC and then it only carries the unbalanced portion of the load.


Yes, most of us know it is a "grounded conductor", but it is just easier to call it a neutral. When I wire a receptacle, I land the hot and neutral wires, not the hot and grounded conductor. I don't think anyone has ever been confused by it.


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## Richard Rowe

Never seen it done... never thought about it and never looked it up. Oh well now I am woundering why you ask that question, what brought it to your mind? I know you said stuff came to your mind when you were at work.


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## JustDave

I was pulling a new phase wire for dual switching T8's in a Canadian tire and a co-worker asked me if it would be ok to share the neutral of another circuit. I gave a reasonable answer but I was incurred with curiosity. I just had to find out a little more.


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## Possum

Ive seen it done several times but usually on a service call where a neutral has been lost. Usually find a melted wire nut or wire burned into inside the panel at the neutral bar.


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## steelersman

Greg said:


> It is only considered a "neutral" on a MWBC and then it only carries the unbalanced portion of the load.


 
What!? So you are saying that if it's not a MWBC then there is no neutral? So this means that my dishwasher which has a 12-2 romex homerun which is 120 volts and the black wire is connected to the 20 amp breaker and the white wire is landed to the neutral/ground bus bar, that the white wire isn't a neutral but instead is a grounded conductor? Are you aware that they are the same thing? Jesus christ man. Wake the "F" up for crying out loud!


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## 480sparky

steelersman said:


> What!? So you are saying that if it's not a MWBC then there is no neutral? So this means that my dishwasher which has a 12-2 romex homerun which is 120 volts and the black wire is connected to the 20 amp breaker and the white wire is landed to the neutral/ground bus bar, that the white wire isn't a neutral but instead is a grounded conductor? Are you aware that they are the same thing? Jesus christ man. Wake the "F" up for crying out loud!


 
Take a breath, step back.......then look for 'neutral' in the '05 or earlier.

Up through the '05, there was a neutral only in MWBCs. Otherwise, it was technically the grounded conductor.

I think the '08 is a step towards bringing the vulgar terms used by field electricians into acceptance.


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## steelersman

480sparky said:


> Take a breath, step back.......then look for 'neutral' in the '05 or earlier.
> 
> Up through the '05, there was a neutral only in MWBCs. Otherwise, it was technically the grounded conductor.
> 
> I think the '08 is a step towards bringing the vulgar terms used by field electricians into acceptance.


oh ok that's better.


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## Larry Fine

steelersman said:


> So this means that my dishwasher which has a 12-2 romex homerun which is 120 volts and the black wire is connected to the 20 amp breaker and the white wire is landed to the neutral/ground bus bar, that the white wire isn't a neutral but instead is a grounded conductor?


Of course, we all know they're the same thing, but technically speaking, what you just said is exactly correct.

I use 'neutral' for grounded, and even 'outlet' for receptacle, and haven't been hit by lightning yet. :whistling2:


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## njspark83

well you wouldnt get 240 volts because even though your sharing the neutral your only going through half of the wound coil back at the transformer. There isn't enough difference in potential. Good insight though nonetheless.


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## zgozvrm

I assume what you're talking about is having the same phases from 2 different panels (supplied by different transformers). If this is the case, you'll be creating a ground loop which is to be avoided.

If instead, you're referring to 2 panels fed from the same transformer, then there would be no problem as long as the neutral is sufficiently large enough to handle the load.


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## crosport

You should'nt use a common neutral for branch circuits supplying equipment.If for whatever reason you lose that neutral a series circuit is created which can reak havoc with the voltages supplying that equipment.Ask me how i know.Our code does'nt allow it for that reason.


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## 480sparky

crosport said:


> You should'nt use a common neutral for branch circuits supplying equipment.If for whatever reason you lose that neutral a series circuit is created which can reak havoc with the voltages supplying that equipment.Ask me how i know.Our code does'nt allow it for that reason.


It's still legal in the states.

It's allowed because there's the presumption that those working on electrical circuits are trained and knowledgable enough to recognize the dangers.

And anyone in the trade should know what happens, and why. Sadly, few actually do.


BTW, are services in Canada basically multi-wires like there are here south of the border?


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## Rob569

crosport said:


> You should'nt use a common neutral for branch circuits supplying equipment.If for whatever reason you lose that neutral a series circuit is created which can reak havoc with the voltages supplying that equipment.Ask me how i know.Our code does'nt allow it for that reason.



When you say a common neutral for branch circuits, do you mean pulling one neutral for three phases in the same pipe? I am curious as to what you mean by this.


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## user438

crosport said:


> You should'nt use a common neutral for branch circuits supplying equipment.If for whatever reason you lose that neutral a series circuit is created which can reak havoc with the voltages supplying that equipment.Ask me how i know.Our code does'nt allow it for that reason.


 
Please, Your code was given to you by us. if we didn't hand you our code you would be feeding recepts with 300 volts like the rest of the world. I personally have always put muliwire branch circuits on a 2 pole breaker way before it was code to tie them together


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## crosport

Just to clarify- it's not a good idea to run a 3 wire circ. supplying recepts. to say something like computers or other expensive equip.Lose the neutral and potentially a piece of equip. can see upto 240V across 2 hots instead of 120V between neutral and 1 hot.Quite often a 3 wire circ. is run to a kitchen which supplies a fridge and micro.Why would you tie the breakers together when if the micro blows the breaker it also takes out your fridge circ.As long as they're on different phases and it isn't required by code why do it? Mind you if the 3 wire goes into a split recept.in a house then the breaker has to be a 2 pole.Oh and thanks for giving us the code next you'll be saying you gave Canada HOCKEY!


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## mattsilkwood

480sparky said:


> Two circuits on the same phase sharing a neutral is permitted by the NEC, AFAIK, but I've never heard of it done.


 I have seen it done many times, but never correctly.


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## Toronto Sparky

Brings to mind those little skinny two pole stablock breakers that FPE sold that could be placed in a position that both were on one phase..

Easy for a home owner to connect two circuits with a three wire to one of these misplaced breakers and cause overload on the neutral even though it looked right.

Got a fews calls over the years from DIYs that could not figure out why the water tank they just connected didn't work even though there was voltage on both wires.


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## mattsilkwood

crosport said:


> Just to clarify- it's not a good idea to run a 3 wire circ. supplying recepts. to say something like computers or other expensive equip.Lose the neutral and potentially a piece of equip. can see upto 240V across 2 hots instead of 120V between neutral and 1 hot.Quite often a 3 wire circ. is run to a kitchen which supplies a fridge and micro.Why would you tie the breakers together when if the micro blows the breaker it also takes out your fridge circ.As long as they're on different phases and it isn't required by code why do it? Mind you if the 3 wire goes into a split recept.in a house then the breaker has to be a 2 pole.Oh and thanks for giving us the code next you'll be saying you gave Canada HOCKEY!


 Every service I have ever seen is a multi wire circuit.


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## Electric Al

Answer to Toronto Sparky.. W.T.H. is the H.O. doing in the panel ?????


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## Toronto Sparky

Electric Al said:


> Answer to Toronto Sparky.. W.T.H. is the H.O. doing in the panel ?????


Home owners do everything these days to save a buck.. Mike Holmes showed them how..


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## Electric Al

Then they call you to come and fix it, then bitch when you charge them !!!! :laughing:


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## wildleg

crosport said:


> Just to clarify- it's not a good idea to run a 3 wire circ. supplying recepts. to say something like computers or other expensive equip.Lose the neutral and potentially a piece of equip. can see upto 240V across 2 hots instead of 120V between neutral and 1 hot.Quite often a 3 wire circ. is run to a kitchen which supplies a fridge and micro.Why would you tie the breakers together when if the micro blows the breaker it also takes out your fridge circ.As long as they're on different phases and it isn't required by code why do it? Mind you if the 3 wire goes into a split recept.in a house then the breaker has to be a 2 pole.Oh and thanks for giving us the code next you'll be saying you gave Canada HOCKEY!


the US didn't give Canada hockey, Chuck Norris gave Canada hockey. And if he wants, he can take it away too.


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