# Shared neutral on same phase?



## Sparkee (Sep 22, 2009)

I'm working a house that's wired using 12-3 romex with the black and red sharing the same neutral. Do you guys think it's best to put them on different phases or put them on the same phase?


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## Fission (May 14, 2010)

Sparkee said:


> I'm working a house that's wired using 12-3 romex with the black and red sharing the same neutral. Do you guys think it's best to put them on different phases or put them on the same phase?


Wow...

Why not put the neutral on the same phase too?


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

Sparkee said:


> I'm working a house that's wired using 12-3 romex with the black and red sharing the same neutral. Do you guys think it's best to put them on different phases or put them on the same phase?


 


No body here can decide that for you,,,,

If you want to melt a perfectly good neutral,,,feel free


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## sparks134 (Jan 30, 2009)

Fission said:


> Wow...
> 
> Why not put the neutral on the same phase too?


 My thought exacly... :no::no:


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## Dennis Alwon (May 9, 2009)

Sparkee said:


> I'm working a house that's wired using 12-3 romex with the black and red sharing the same neutral. Do you guys think it's best to put them on different phases or put them on the same phase?


The ungrounded conductors must be on different phases in order for it to work properly. In fact, landing them on the same phase would not be legal.

When the wires are landing on opposite phases the neutral will carry the unbalanced current or the difference between the phases. Thus if you have 10 amps on phase "A" and 15 amps on phase "B" then the neutral only carries 5 amps.

Now put them on the same phase and the neutral will carry the sum of the phases. Thus 15 plus 10 equal 25 amps which would overload a #12 neutral.


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## NolaTigaBait (Oct 19, 2008)

I really think that many people don't understand why you need to put them on opposite phases...Nice explanation Dennis.


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## Sparkee (Sep 22, 2009)

Dennis Alwon said:


> The ungrounded conductors must be on different phases in order for it to work properly. In fact, landing them on the same phase would not be legal.
> 
> When the wires are landing on opposite phases the neutral will carry the unbalanced current or the difference between the phases. Thus if you have 10 amps on phase "A" and 15 amps on phase "B" then the neutral only carries 5 amps.
> 
> Now put them on the same phase and the neutral will carry the sum of the phases. Thus 15 plus 10 equal 25 amps which would overload a #12 neutral.


I was thinking that if it was on a different phase and I lost the neutral for whatever reason there might be a problem with 220 volts but like you are saying putting them on the same phase the wire will carry the sum of the current and it could get hot and since there is no protection it be a potential problem.


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## NolaTigaBait (Oct 19, 2008)

Sparkee said:


> I was thinking that if it was on a different phase and I lost the neutral for whatever reason there might be a problem with 220 volts but like you are saying putting them on the same phase the wire will carry the sum of the current and it could get hot and since there is no protection it be a potential problem.


Thinking? Dude, don;t put them on the same phase and let's leave it at that:thumbsup:


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## Sparkee (Sep 22, 2009)

NolaTigaBait said:


> Thinking? Dude, don;t put them on the same phase and let's leave it at that:thumbsup:


Thinking, it always gets me in trouble.


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## 480sparky (Sep 20, 2007)

Sparkee said:


> I was thinking that if it was on a different phase and I lost the neutral for whatever reason there might be a problem with 220 volts .........



You are correct.

Just make sure your neutrals are all made up nice & tight, and your hots are on opposite phases, and life will be good.


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## Dennis Alwon (May 9, 2009)

Sparkee said:


> I was thinking that if it was on a different phase and I lost the neutral for whatever reason there might be a problem with 220 volts but like you are saying putting them on the same phase the wire will carry the sum of the current and it could get hot and since there is no protection it be a potential problem.


Your thinking is 100% correct if you lose a neutral there is a big oops. That is one reason I do not like MWBC. Here is a quick graphic that may help visualize the situation.


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## 480sparky (Sep 20, 2007)

Dennis Alwon said:


> Your thinking is 100% correct if you lose a neutral there is a big oops. That is one reason I do not like MWBC. Here is a quick graphic that may help visualize the situation.


Why would only load 2 have 240V? Why not load 1?


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## Dennis Alwon (May 9, 2009)

480sparky said:


> Why would only load 2 have 240V? Why not load 1?


It's just a graphic to get the point across. Generally one phase will get 120V first and blow it out and stop the flow so the other phase will not be affected. I have never seen a case where both phases were affected. Theoretically you are right but practically it has not been my experience.


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## 480sparky (Sep 20, 2007)

Dennis Alwon said:


> It's just a graphic to get the point across. Generally one phase will get 120V first and blow it out and stop the flow so the other phase will not be affected. I have never seen a case where both phases were affected. Theoretically you are right but practically it has not been my experience.



What each load will receive for voltage depends on the resistance. The higher the resistance, the higher the voltage. 

If the loads are equal, then both loads would still 'see' 120v. The bigger the difference in the resistances of the two loads, the bigger the voltage disparity will be. If it's high enough, the magic smoke will be released, opening the circuit. Then the other half will drop to 0 volts since there cannot be any current flow.



I know you know this, Dennis, I'm just posting it to explain the dangers inherent to MWBCs. It's a difficult concept to understand at first, but once you comprehend it, it all makes sense.


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## Dennis Alwon (May 9, 2009)

480sparky said:


> What each load will receive for voltage depends on the resistance. The higher the resistance, the higher the voltage.
> 
> If the loads are equal, then both loads would still 'see' 120v. The bigger the difference in the resistances of the two loads, the bigger the voltage disparity will be. If it's high enough, the magic smoke will be released, opening the circuit. Then the other half will drop to 0 volts since there cannot be any current flow.


Good explanation. I should have carried mine further.:thumbsup:


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## 480sparky (Sep 20, 2007)

Here's a real-world expanation:

Here's four meters hooked up to a 240 circuit, with two lamps in series. With both lamps being 100 watts, you can see the voltage and amperage of the entire circuit. From left to right, the meters are reading:

1. Left lamp voltage
2. Circuit voltage
3. Circuit current
4. Right lamp voltage











When I replace the left lamp with a 60 watt, here's what happens:










The 60w (with more resistance), jumps to 191.39 volts, while the 100w drops to 56.7 volts. You can also see the amperage has dropped since a 60w lamp consumes less current than a 100w lamp.

If I were to replace the 60 with a 40, the voltage differences would be greater, and going to a 25 or 15 would make the difference would be greater still. Somewhere along the line, the lower-wattage lamp would (in theory) burn out.​


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## crosport (Apr 4, 2010)

And if you have 2 balanced 120v loads on that split circ.shown above the neutral can be totally disconnected without disturbing the circuit.The neutral carries the difference between the 2 loads and if the loads are the same the neutral carries 0 amps. and the circ. is now a series circ.


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## jwjrw (Jan 14, 2010)

480sparky said:


> Here's a real-world expanation:
> 
> Here's four meters hooked up to a 240 circuit, with two lamps in series. With both lamps being 100 watts, you can see the voltage and amperage of the entire circuit. From left to right, the meters are reading:
> 
> ...


 


I read a story where a guy would kill his employees and keep their stuff.....Most were drifters so no one missed them...How long have you been knocking off drifting electricians and keeping their fluke meters?:whistling2::laughing: Great post by the way!:thumbsup:


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## 480sparky (Sep 20, 2007)

jwjrw said:


> I read a story where a guy would kill his employees and keep their stuff.....Most were drifters so no one missed them...How long have you been knocking off drifting electricians and keeping their fluke meters?:whistling2::laughing: Great post by the way!:thumbsup:


Never having employees, I've never had the urge to kill them. I got receipts for each and every one of those meters, though.

But there are people, however, that I would like to kill.:whistling2:


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## BuzzKill (Oct 27, 2008)

480sparky said:


> Never having employees, I've never had the urge to kill them. I got receipts for each and every one of those meters, though.
> 
> But there are people, however, that I would like to kill.:whistling2:


Actually, accounting-wise, you are the employee AND owner so you get to get paid in twice the cheese!


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## 480sparky (Sep 20, 2007)

BuzzKill said:


> Actually, accounting-wise, you are the employee AND owner so you get to get paid in twice the cheese!


I'm also the secretary, treasurer, accountant, tax preparer, marketer, bookkeeper, manager, foreman, supervisor, estimator, collections agent, web designer, service technician, chief scheduler, mail clerk, vehicle mechanic, license holder, and head garbage can emptier.

Man, do I get a _lot_ of cheese every week!


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## Bob Badger (Apr 19, 2009)

You forgot the big one .... :laughing:


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## BuzzKill (Oct 27, 2008)

480sparky said:


> I'm also the secretary, treasurer, accountant, tax preparer, marketer, bookkeeper, manager, foreman, supervisor, estimator, collections agent, web designer, service technician, chief scheduler, mail clerk, vehicle mechanic, license holder, and head garbage can emptier.


I'd love to hear all of you talking at once.


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## 480sparky (Sep 20, 2007)

Bob Badger said:


> You forgot the big one .... :laughing:



Being a tool doesn't pay well. We don't have a Tool Union. :no:


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## Voltech (Nov 30, 2009)

480sparky said:


> I'm also the secretary, treasurer, accountant, tax preparer, marketer, bookkeeper, manager, foreman, supervisor, estimator, collections agent, web designer, service technician, chief scheduler, mail clerk, vehicle mechanic, license holder, and head garbage can emptier.*Trained Monkey*
> 
> Man, do I get a _lot_ of cheese every week!


fixed it for ya :thumbsup:


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## 480sparky (Sep 20, 2007)

Voltech said:


> fixed it for ya :thumbsup:



That's me..... trained monkey!


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## idontknow (Jul 18, 2009)

Dennis Alwon said:


> The ungrounded conductors must be on different phases in order for it to work properly. *In fact, landing them on the same phase would not be legal.*
> 
> When the wires are landing on opposite phases the neutral will carry the unbalanced current or the difference between the phases. Thus if you have 10 amps on phase "A" and 15 amps on phase "B" then the neutral only carries 5 amps.
> 
> Now put them on the same phase and the neutral will carry the sum of the phases. Thus 15 plus 10 equal 25 amps which would overload a #12 neutral.


I can't find this in the code book, got a reference? I was at a job where a neutral was run oversized to carry the full load of the 2 circuits. Both were on the same phase.


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## 480sparky (Sep 20, 2007)

idontknow said:


> I can't find this in the code book, got a reference? I was at a job where a neutral was run oversized to carry the full load of the 2 circuits. Both were on the same phase.



Try complying with 210.4(B).


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## Voltech (Nov 30, 2009)

480sparky said:


> Try complying with 210.4(B).


Not a problem for those of us on the 05 cycle..


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## 480sparky (Sep 20, 2007)

Voltech said:


> Not a problem for those of us on the 05 cycle..



The 2005 is so, well, 2005-ish.


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## Dennis Alwon (May 9, 2009)

idontknow said:


> I can't find this in the code book, got a reference?





480sparky said:


> Try complying with 210.4(B).


Sparky is correct. When I wrote that I thought someone was going to challenge this but remember the OP stated 12/3 romex. You cannot upsize the neutral even if you are on the 2005 NEC. 

Gotcha twice.


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## 480sparky (Sep 20, 2007)

Dennis Alwon said:


> Sparky is correct. When I wrote that I thought someone was going to challenge this but remember the OP stated 12/3 romex. You cannot upsize the neutral even if you are on the 2005 NEC.
> 
> Gotcha twice.






Sparkee said:


> *I'm working a house* that's wired using 12-3 romex with the black and red sharing the same neutral. Do you guys think it's best to put them on different phases or put them on the same phase?


210.4(B) goes back to 1981 for dwellings.

Got 'im three times, Dennis!


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## idontknow (Jul 18, 2009)

480sparky said:


> Try complying with 210.4(B).


2 pole switch at the panel


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## idontknow (Jul 18, 2009)

Dennis Alwon said:


> Sparky is correct. When I wrote that I thought someone was going to challenge this but remember the OP stated 12/3 romex. You cannot upsize the neutral even if you are on the 2005 NEC.
> 
> Gotcha twice.


So where does it say you can't land em on the same phase? Identified handle ties are also allowed and can be spread across to link 2 of the same phase together.


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## NolaTigaBait (Oct 19, 2008)

idontknow said:


> So where does it say you can't land em on the same phase? Identified handle ties are also allowed and can be spread across to link 2 of the same phase together.


I don;t understand why you would want to land them on the same phase regardless....Don't you want to balance the loads as well as cancel teh neutral load?


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## 480sparky (Sep 20, 2007)

idontknow said:


> 2 pole switch at the panel



"....at a point where the branch circuit originates".

It originates in the panel, not next to it.


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## idontknow (Jul 18, 2009)

NolaTigaBait said:


> I don;t understand why you would want to land them on the same phase regardless....Don't you want to balance the loads as well as cancel teh neutral load?


I saw it once and attempted to challenge it. I can never fully understand what goes through peoples minds and why they wire things up so strangely. I couldn't find a basis to say it was not legal so when Dennis said it wasn't, I pressed him for the reference. Since then I have read 210.4B and noticed the change in 08. In trying to keep the question relevant I'm now having to build a scenario where it could still happen. Bear with me folks.

I now remember handle ties only are allowed up to 2 poles.

The panel is 120 volt only. Therefore 2 breakers next to each other would be on the same phase.

Three phase breaker in a single phase panel? There's my next stab at an answer.


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## 480sparky (Sep 20, 2007)

idontknow said:


> .............I now remember handle ties only are allowed up to 2 poles.


Huh?!?!



idontknow said:


> The panel is 120 volt only. Therefore 2 breakers next to each other would be on the same phase.


I'll buy that for a dollar.



idontknow said:


> Three phase breaker in a single phase panel? There's my next stab at an answer.


Legal, but an exceedingly poor design.


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## idontknow (Jul 18, 2009)

480sparky said:


> Huh?!?!


from mh forum


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