# Individual Neutrals on Dimmers



## Esoteric (Mar 16, 2010)

Hey guys. Am I going nuts? I seem to remember in all the installation manuals I have read (mostly ETC and Strand) that each circuit (dimmer) must have its own neutral. But I have an electrician on-site trying to tell me that he wants to wire them all with a common neutral and it should work fine (and give you individual control of all the circuits) because the hot wire controls how much power the unit gets. Two things...

1. Am I going nuts or does each circuit (dimmer) need its own neutral?
2. If so, why (other than the manufacturer says so, which is enough for me but not for some people)?

Mike


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## starksk (Mar 16, 2010)

From ETC Application Note 104-2 and this Wiki Article:

> In non-dimmed applications, branch circuits are often installed with three circuits sharing a common neutral conductor, where each of the three circuits is on a different phase. This is known as a “multiwire” branch circuit arrangement. It is used to save costs because only four total conductors (three hot, one neutral) are used to feed three branch circuits.
> 
> This type of multi-wire branch circuit arrangement is not recommended for use with phase-control dimmers on new installations because it can cause voltage-drop interaction between the three branch circuits, as well as neutral conductor overloading.
> 
> ...


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## ajb (Mar 16, 2010)

Kirk's got it in one. This is one of the reasons you really want to have an electrical contractor who has experience with these sorts of dimming systems do any work on them. There are a number of factors that just don't come up in wiring, say, a store or restaurant that can be very important in entertainment venues. 

Although without knowing what your local code body is like, it's possible that what the electrician is proposing will meet code. The wording of the 2002 NEC, for example, is not so explicit in requiring simultaneous disconnection on multiwire branch circuits.


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## Esoteric (Mar 16, 2010)

Thanks guys. My normal installer sends individual neutrals to each light. This guy just wanted to argue about it. Last time I use him.

Mike


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## derekleffew (Mar 16, 2010)

Esoteric's situation appears to be resolved. 

But to further discussion, I've heard "urban legend" of a touring lighting system by a promoter of "family entertainment" type shows using 12/37 cable for the hots (not sure how many, with some wires as ground) and a separate 4/0 wire for neutrals. *Other than the pesky code-compliance issues,* it seems workable, as all the neutrals are tied together in the dimmer rack anyway. Of course, this required special break-out boxes on the truss. 

Thoughts?


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## Footer (Mar 16, 2010)

derekleffew said:


> Esoteric's situation appears to be resolved.
> 
> But to further discussion, I've heard "urban legend" of a touring lighting system by a promoter of "family entertainment" type shows using 12/37 cable for the hots (not sure how many, with some wires as ground) and a separate 4/0 wire for neutrals. *Other than the pesky code-compliance issues,* it seems workable, as all the neutrals are tied together in the dimmer rack anyway. Of course, this required special break-out boxes on the truss.
> 
> Thoughts?



Better get that truss in the air before the inspector stops by....

Its kind of the same argument as to why you have to run a ground and a neutral to a circuit when they both terminate to the same terminal bus. You can get away with it, but it makes you feel ucky.


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## MNicolai (Mar 16, 2010)

Don't _not_ use an electrician based on having to argue with him. In theatre, we do plenty of things that are otherwise unorthodox. They work, but they sometimes tend to go against convention. If he was arguing with you, it was unlikely he intended to violate code (though he would have), but rather you (the client) was telling him (the experienced tradesman) how to do his job, and what you were telling him defied his usual practices.

The reason you should not use him in the future should be based more on his clear inexperience with theatrical applications. There's no need to blame him; many electricians don't wire for theatre, and often when they do for the first time, it's a learning experience.

I'm lucky enough to do most of my work with a school district that has their own master electrician (the actual kind, not the lighting variety). Through several projects with him, he's been progressively learning more and more about the differences of wiring for theatre. That actually turned our last meeting, which was only supposed to last an hour and a half, into a six and a half hour meeting discussing all of our different options and what we could or could not use in a theatre application. He admits that he's trying to be a lot more open-minded and if I made some of the requests to him three years ago that I make to him now, he'd probably have laughed me out of the room. We also have another electrician that we outsource some projects to, and both the district electrician and myself like going to him because he's willing to learn. He's not a theatrical electrician by any means, but we know we can trust our projects to him, despite them being out of his usual area of expertise.

In theatre, just sort of do things. We have our ways, and the rest of the world has theirs. It's not that we're wrong, or that they're wrong, but it's a very specific application that we use our electrical under, which requires some more careful examining of what's going on. In some regards, it's far more difficult than wiring a house. We're very picky about our electrical.

Common phrases I've heard while talking to electricians over the last couple years include...

"I could power *8 homes* with the amount of electricity you want to turn on a sound system."
"Why would you use single conductor cables when you could power everything using pin & sleeve connectors?" (hint: singles are far easier to rent, replace, and purchase)
(after discussing 19-pin connectors for two hours) "You're kidding me -- those connectors only cost ___ each?! I've been arguing against them thinking they would cost fifteen times that, because many of the near-equivalents I typically use are that expensive."
"What's the advantage of using your "Stage Pin" connectors over typical 5-15's?"

If you can't find an electrician who knows theatre, find one who is willing to learn. Don't not choose one based on him trying to do your project an easier/cheaper way in an attempt to achieve the same results. That's what your electrician was trying to do, and it'd be too much to expect him to know that little tidbit of code about separate neutrals off of the top of his head. Most electricians will never work in a theatre, and won't be exposed to anything in that lovely section of the NEC dedicated solely to us. The electrician you want to be afraid of is the one not only is beyond their expertise, but also refuses to acknowledge there are reasons he/she shouldn't perform their work as they normally would.


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## JD (Mar 16, 2010)

Need? or Should? You can run with a common neutral and the system will work, but you should not. In all cases, code requires independent circuits to home run the neutral when common trip is not in use. (Can't think of any that don't.) Common trip applications, such as a 3 phase motor with no neutral are the obvious exception. Even in home construction, 12/3 wg wire is becoming rare in favor of running two runs of 12/2 wg. (That may actually be required now, wasn't 30 years ago.) The exceptions are appliances (ovens, driers, etc) that use common trip breakers. (Although that's usually 10 or thicker.) When it comes to theater, I have never seen an application (even old ones) that use a common neutral. (Although I am sure there are some hiding out there.)


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## mrb (Mar 18, 2010)

derekleffew said:


> Esoteric's situation appears to be resolved.
> 
> But to further discussion, I've heard "urban legend" of a touring lighting system by a promoter of "family entertainment" type shows using 12/37 cable for the hots (not sure how many, with some wires as ground) and a separate 4/0 wire for neutrals. *Other than the pesky code-compliance issues,* it seems workable, as all the neutrals are tied together in the dimmer rack anyway. Of course, this required special break-out boxes on the truss.
> 
> Thoughts?



as long as you complete the circuit its going to work, but two immediate problems come to mind (besides the code issue) running seperate like that is going to cause quite a bit of electromagnetic interference, and any time you have current passing in one direction through a closed loop of ferrous metal (do the pyle connectors have steel shells?) you get inductive heating.


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## mrb (Mar 18, 2010)

JD said:


> Need? or Should? You can run with a common neutral and the system will work, but you should not. In all cases, code requires independent circuits to home run the neutral when common trip is not in use. (Can't think of any that don't.) Common trip applications, such as a 3 phase motor with no neutral are the obvious exception. Even in home construction, 12/3 wg wire is becoming rare in favor of running two runs of 12/2 wg. (That may actually be required now, wasn't 30 years ago.) The exceptions are appliances (ovens, driers, etc) that use common trip breakers. (Although that's usually 10 or thicker.) When it comes to theater, I have never seen an application (even old ones) that use a common neutral. (Although I am sure there are some hiding out there.)



the main thing driving the elimination of MWBCs in residential construction is AFCI breakers which require each circuit to have an individual neutral landed on the breaker. The cable manufacturers came up with 12-2-2 which is two hots and two neutrals (one with a red stripe) for runs of two circuits in one cable but it is not widely used. The handle tie rule is beginning to chip away at use of MWBCs in commercial due to having to shut down three circuits to work on one. Now you mostly see them supplying things with one 5 wire circuit (well 4 + ground) such as 4P5W connectors (ie L21-30), prewired modular office furniture, things of that nature.


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## Esoteric (Mar 18, 2010)

Yeah, the issue resolved itself.

It is not his lack of knowledge that made me not want to work with him again. But the fact that after I pointed out that the manufacturers installation instructions mandated a certain way he still wanted to argue that makes me want to not work with him again.

So, just as a hypothetical, if you did run a common neutral you would still have control over individual dimmers if they have individual hots, right?

Mike


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## mrb (Mar 18, 2010)

Esoteric said:


> Yeah, the issue resolved itself.
> 
> It is not his lack of knowledge that made me not want to work with him again. But the fact that after I pointed out that the manufacturers installation instructions mandated a certain way he still wanted to argue that makes me want to not work with him again.
> 
> ...



it would work, but youre going to have problems. Steveterry would be the authority on this.


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## MNicolai (Mar 18, 2010)

Electrically, it would still allow you independent control over each circuit, but the reason common neutrals are disallowed is as Kirk mentioned:


> This type of multi-wire branch circuit arrangement is not recommended for use with phase-control dimmers on new installations because it can cause voltage-drop interaction between the three branch circuits, as well as neutral conductor overloading.


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## ajb (Mar 18, 2010)

The reason common neutrals are _disallowed_ is the handle-tie issue, which has to do with personal safety of the people who will service those circuits in the future. 

The reason they are _not recommended_ is because of the voltage drop and neutral overload issues, which can be compensated for by increasing the size of the neutral conductor. However, this is not a common practice in multiwire branch circuits*, and it's typically a good idea to stick to standard practices as much as you can when these systems get spec'ed and installed so widely. 

* It is a common practice and required by the NEC where non-linear and significant harmonic loads comprise a large portion of the loads on a feeder.


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## mstaylor (Mar 18, 2010)

I had a situation years ago where the electrician and I had a problem. He wired a stage of border strips,four color, incorrectly. The board was wired with the lights being tied directly to the dimmer, no patch ability. What he did incorrectly was he tied 1 through 4 as a dimmer, 5 through 8 as the next and so forth. Obviously this makes color mixing a little tough. There were no rondels in them so I couldn't make him understand the problem. I told him he could just swap the hots around on the breakers. He said it would cause a neutral problem because they were individual on the border. I explained because it went to a common nuetral block it would be fine. When the owner finally came in he agreed with me. I have always wondered if I was indeed correct or not.


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## JChenault (Mar 18, 2010)

ajb said:


> The reason common neutrals are _disallowed_ is the handle-tie issue, which has to do with personal safety of the people who will service those circuits in the future.



I must be wearing my stupid hat today. Can you explain what you mean by 'handle-tie issue'. I am not familiar with the term.

Thanks


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## JD (Mar 18, 2010)

JChenault said:


> I must be wearing my stupid hat today. Can you explain what you mean by 'handle-tie issue'. I am not familiar with the term.
> 
> Thanks



That the breaker handles are literally tied together as in a common trip 20a X 2.

For example, lets say you had 12/3 wg tied to two single 20 amp breakers. You turn one off. The wire running to and from the breaker may still be live if there is any 240 volt appliances on the circuit. Also, even with the breaker off and no 240 volt appliances, you have current returning on the neutral from the other half of the circuit. By tying the "handles" together, you insure that both branches are off. 

As for Ground Fault Interrupts, the neutral must be independent as the breaker monitors the current flow balance on the hot and the neutral and trips on imbalance.


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