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Split Circuits


homnspector
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I'm wondering if anyone else has tried to tackle the issue of split circuits in the breaker panel. Red and black wires on adjacent 110 breakers usually indicates a shared neutral. 2 electricians I have asked stated that these should be installed on 2 pole internal trip breakers. The neutral may be energized by the adjacent circuit, creating a hazard for anyone working on the circuit even though the breaker for the specific appliance or circuit is turned off.

Last time I called this out, the builders electrician said it was not a problem, was not prohibited by NEC unless both circuits serve the same outlet (top and bottom 1/2 of the outlet on different circuits). Looking it up in NEC, I see that a 2 pole breaker is not required but trust my electricians who say single pole breakers are not safe for split circuits. I have pretty much given up calling it out as I see it constantly. Any feedback is appreciated.

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Originally posted by homnspector

I'm wondering if anyone else has tried to tackle the issue of split circuits in the breaker panel. Red and black wires on adjacent 110 breakers usually indicates a shared neutral. 2 electricians I have asked stated that these should be installed on 2 pole internal trip breakers. The neutral may be energized by the adjacent circuit, creating a hazard for anyone working on the circuit even though the breaker for the specific appliance or circuit is turned off.

Last time I called this out, the builders electrician said it was not a problem, was not prohibited by NEC unless both circuits serve the same outlet (top and bottom 1/2 of the outlet on different circuits). Looking it up in NEC, I see that a 2 pole breaker is not required but trust my electricians who say single pole breakers are not safe for split circuits. I have pretty much given up calling it out as I see it constantly. Any feedback is appreciated.

Every electrician out there knows about multi-wire circuits and how to safely work with them. In a lot of commercial wiring they're the rule, not the exception. The only time they becomes dangerous is when an amateur is messing with the wiring. I happen to be one of those people who think we should not be designing our electrical systems to coddle to amateurs.

As far as I'm concerned, there is no "issue" to tackle. The NEC is abundantly clear on the subject. My advice is to let them be.

- Jim Katen, Oregon

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Originally posted by Jim Katen

Every electrician out there knows about multi-wire circuits and how to safely work with them.

I gotta say, that's an unKaten-like overstatement. Half the licensed guys around here can't even wire a simple sub panel correctly, and that's only the tip of the iceburg.

Brian G.

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I found more info on this at the ASHI website

Notes regarding multiwire (shared-neutral) branch circuits

1. For a detailed article about how these circuits are wired, see the ASHI

Technical Journal, Vol 2 No 1 Winter 1992 p. 27-30 In addition to the author,

Neal Macneale III, Douglas Hansen and Dan Friedman edited and illustrated this

material.

2. Use of linked double-pole or two-pole circuit breakers is recommended:

Pending further research and development of authoritative citations, the

following is the opinion of the author:

Multiwire branch circuits should be protected by a double-pole common-internal

trip circuit breaker, including the physical "trip tie" which bonds

the two circuit breaker switches together. This is a safety measure which

protects people working on the building wiring and which helps assure that the

circuit is wired properly at the panel. Even if local building inspectors do

not require this measure we recommend it as a safety item and as good

construction practice.

Explanation:

a. Required by National Electrical Code for split receptacles, as per paragraph

210-4-b.

b. Using a double-pole breaker assures that the two legs of the circuit will be

forced (in most panels) to opposite legs of the 240-volt panel - a requirement

when circuits use a shared neutral, such as in multiwire branch circuits. If

individual 120V breakers are used, it's possible for a future modification or

rearrangement of breakers in the panel to in advertently move one or both

individual breakers so that they both end up on the same 120V leg of the panel

- which is improper when a shared neutral is involved. (Improper because the

shared unbalanced load could exceed the rating of the wire.)

c. Using a double-pole assures that if one leg of the circuit is being turned

off for electrical repair/modification work in the building, the other leg is

forced off as well. Otherwise it is possible for the mechanic to be shocked

while working on the circuit, since the neutral wire of the supposedly "dead"

circuit could be carrying current from the sister "live" circuit.

3. Electrical code notes:

3.a. ASHI Member Frank Luciano spoke with Al Weiss, New York State building

code authority (Building code support office at World Trade Center, New York

City) regarding the requirement for linking or common-trip ties for these

circuits. Mr. Weiss' opinion was that if he sees individual breakers in the

panel on a multiwire circuit he will not call it out as an issue for failure to

link the breakers together. The discussion did not review possible relocation

of one of the breakers to the same phase or "leg" of the panel as the other.

Mr. Weiss interpretation of the National Electric Code is that if, on a

multiwire circuit, the two phases are wired to the same electrical receptacle

(upper portion to one phase, lower to another phase, by breaking the tie on the

receptacle sides) then a common-trip breaker should be used on that circuit. He

also opined that if breakers were wired in parallel, rather than in series, as

is done in some states, then common trip ties are not required.

http://www.inspect-ny.com/electric/multiwir.htm

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Originally posted by homnspector

I found more info on this at the ASHI website

Notes regarding multiwire (shared-neutral) branch circuits

1. For a detailed article about how these circuits are wired, see the ASHI

Technical Journal, Vol 2 No 1 Winter 1992 p. 27-30 In addition to the author,

Neal Macneale III, Douglas Hansen and Dan Friedman edited and illustrated this

material.

That's a really great article on the subject. It's worth the cost of that back issue just to read the article. However, the article is very careful to avoid any discussion at all of the use of handle ties on multi-wire circuits. I suspect that the editors had some differnces of opinions on the subject and elected to avoid the issue entirely.

2. Use of linked double-pole or two-pole circuit breakers is recommended:

Pending further research and development of authoritative citations, the

following is the opinion of the author:

Did you catch that? The entire idea of putting these on common-trip breakers is Dan's opinion. He even says he can't find any authoritative source for this opinion. I like Dan. I respect Dan. But sometimes he comes up with real doozys.

Multiwire branch circuits should be protected by a double-pole common-internal

trip circuit breaker, including the physical "trip tie" which bonds

the two circuit breaker switches together. This is a safety measure which

protects people working on the building wiring and which helps assure that the

circuit is wired properly at the panel. Even if local building inspectors do

not require this measure we recommend it as a safety item and as good

construction practice.

That's some decent logic, but that's all. There are dozens, maybe even hundreds of things that we could recommend that would make an electrical system safer that go above and beyond the NEC requirements. Why choose this particular one as a poster child?

Explanation:

a. Required by National Electrical Code for split receptacles, as per paragraph

210-4-b.

Nope. That cite does not support his position. It's only dealing with a situation where you've got more than one device on the same yoke.

b. Using a double-pole breaker assures that the two legs of the circuit will be

forced (in most panels) to opposite legs of the 240-volt panel - a requirement

when circuits use a shared neutral, such as in multiwire branch circuits.

Nope. Wrong again. It is not a "requirement."

If

individual 120V breakers are used, it's possible for a future modification or

rearrangement of breakers in the panel to in advertently move one or both

individual breakers so that they both end up on the same 120V leg of the panel

- which is improper when a shared neutral is involved. (Improper because the

shared unbalanced load could exceed the rating of the wire.)

c. Using a double-pole assures that if one leg of the circuit is being turned

off for electrical repair/modification work in the building, the other leg is

forced off as well. Otherwise it is possible for the mechanic to be shocked

while working on the circuit, since the neutral wire of the supposedly "dead"

circuit could be carrying current from the sister "live" circuit.

All true. But it's not a requirement. He's trying to make it sound as if it is.

3. Electrical code notes:

Oops. Looks like he couldn't find any.

3.a. ASHI Member Frank Luciano spoke with Al Weiss, New York State building

code authority (Building code support office at World Trade Center, New York

City) regarding the requirement for linking or common-trip ties for these

circuits. Mr. Weiss' opinion was that if he sees individual breakers in the

panel on a multiwire circuit he will not call it out as an issue for failure to

link the breakers together. The discussion did not review possible relocation

of one of the breakers to the same phase or "leg" of the panel as the other.

Mr. Weiss interpretation of the National Electric Code is that if, on a

multiwire circuit, the two phases are wired to the same electrical receptacle

(upper portion to one phase, lower to another phase, by breaking the tie on the

receptacle sides) then a common-trip breaker should be used on that circuit. He

also opined that if breakers were wired in parallel, rather than in series, as

is done in some states, then common trip ties are not required.

So the only authority he consulted told him he was wrong.

- Jim Katen, Oregon

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Do you know what these circuits operate? Up here in Alberta, our kitchen recpeptacles are are required to be "split receptacles" where the top and bottom halves of the receptacle are essentially on seperate circuits, but share a nuetral. I understand that is not required in the USA after talking to some Denver Area inspectors. Does this help?

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  • 3 years later...
Originally posted by homnspector

Well Jim, I see this the handle tie is now a requirement in the 2008 NEC. (210.4 requires simultaneous disconnecting of all ungrounded conductors of multiwire branch circuits.) Will you be recommending it now? Or do you still believe " there is no "issue" to tackle."

Well, obviously Code Panel 2 didn't consult me on this one . . .

Yes. It's a requirement as of the 2008 NEC. I'll be recommending it wherever I find it missing in buildings that were permitted after April 1, 2008, the date that Oregon adopted the 2008 NEC. Such an installation would be a violation of the NEC.

I probably won't be flagging it in the hundreds of thousands of multi-wire circuits that were wired with it before that. In practical terms, I still see it as a pissant issue.

- Jim Katen, Oregon

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I probably overreact to this. I know only 2 electricians well. One was about electrocuted from a hot neutral on a disposal circuit. The other one always installs 2-pole breakers for multi-wire circuits. So, early in my career I assumed that was the way it was supposed to be. I have probably pissed off alot of electricians and sellers over the years. I am glad to see it in the NEC. Thanks jgclancy for posting that.

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Originally posted by msteger

Some electricians use this method as a way to save money and labor (less wire).

This is just an easy knee-jerk comment about this subject.

MOST electricians use MWBC's, and cost is rarely the main issue. There are several good reasons to use them.

As has been stated, MWBC's in commercial work are the rule, not the exception.

Originally posted by Jim Katen

Every electrician out there knows about multi-wire circuits and how to safely work with them. In a lot of commercial wiring they're the rule, not the exception. The only time they becomes dangerous is when an amateur is messing with the wiring. I happen to be one of those people who think we should not be designing our electrical systems to coddle to amateurs.

As far as I'm concerned, there is no "issue" to tackle. The NEC is abundantly clear on the subject. My advice is to let them be.

I could not agree more!
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Originally posted by Jim Katen

Yes. It's a requirement as of the 2008 NEC. I'll be recommending it wherever I find it missing in buildings that were permitted after April 1, 2008, the date that Oregon adopted the 2008 NEC. Such an installation would be a violation of the NEC.

I probably won't be flagging it in the hundreds of thousands of multi-wire circuits that were wired with it before that. In practical terms, I still see it as a pissant issue.

Once again, I totally agree!
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Originally posted by Speedy Petey

Originally posted by msteger

Some electricians use this method as a way to save money and labor (less wire).

This is just an easy knee-jerk comment about this subject.

MOST electricians use MWBC's, and cost is rarely the main issue. There are several good reasons to use them.

As has been stated, MWBC's in commercial work are the rule, not the exception.

Its a knee jerk comment from a well known electrician I have talked to about this in the past.

Originally posted by Jim Katen

Every electrician out there knows about multi-wire circuits and how to safely work with them. In a lot of commercial wiring they're the rule, not the exception. The only time they becomes dangerous is when an amateur is messing with the wiring. I happen to be one of those people who think we should not be designing our electrical systems to coddle to amateurs.

As far as I'm concerned, there is no "issue" to tackle. The NEC is abundantly clear on the subject. My advice is to let them be.

I could not agree more!

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