2008 NEC 210.4 Multiwire Branch Circuits

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bdorner

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There currently has been a lot of discussion around article 210.4 (A) (B). We were looking for a better definition on what is considered a Multiwire branch circuit as well as how this effects the circuiting of the miscellaneous electrical componants.

It was our understanding that if you have a duplex recetacle spilt wired that it would need to be fed with a two pole breaker in lieu of two 120v 20a branch circuits. Would this also apply if you were feeding a troffer with (2) ballast doing inner/outer control (as an example).

How does this apply to site lighting when you have a site fixture that has three luminaires where one luminaire is wired to a "NL" circuit and the other two are wired to normal control.

Also what about furniture systems.


Sorry first time posting and had a lot to get put into this. Will work on my delivery
 
Did you look at the NEC definition of a MWBC?
I find it interesting that we know what something is until a new requirment costs us money. Examples:
Kitchens and GFCIs-what is a kitchen?
Vending machines and GFCIs-what is a vending machine?

I suspect MWBC are a thing of the past...
 
The NEC published definition prorbably covers this as well as any of us can.
 
Here's the NEC definition.

"Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system."

Chris
 
bdorner said:
It was our understanding that if you have a duplex recetacle spilt wired that it would need to be fed with a two pole breaker in lieu of two 120v 20a branch circuits. Would this also apply if you were feeding a troffer with (2) ballast doing inner/outer control (as an example).
Click to expand...

Even with two 120 volt, 2 wire circuits feeding the rec a handle tie would be required. 210.7(B).


bdorner said:
Also what about furniture systems.
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Furniture systems require all MWBC's to have a simultaneous disconnecting means. 605.6, 605.7.
 
follow up

follow up

Thank you you for the overview and yes I did look at the definition for a multiwire branch circuit.

So then do you deal with a large room of troffers that has a night light circuit and multiple lighting circuits. Then do you have to go a put in multiple night light circuits so that you are incompliance?

Sorry for the ignorance but I am trying to understand the implementation.

What about site lighting where you have multiple 2pole branch breakers serving a site fixture. Are you now not able to do a night light circuit on a pole?
 
bdorner said:
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So then do you deal with a large room of troffers that has a night light circuit and multiple lighting circuits. Then do you have to go a put in multiple night light circuits so that you are incompliance?
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If the circuits share a neutral you need a means of common disconnect for those circuits. This would not change the number of night light circuits that would be required.
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What about site lighting where you have multiple 2pole branch breakers serving a site fixture. Are you now not able to do a night light circuit on a pole?
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There was no change in the rules for circuits fed from two pole breakers.
 
raider1 said:
Here's the NEC definition.

"Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system."

Chris
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So if I bring the high-leg of a delta along for the ride, it is no longer a multiwire branch circuit?

Might be very unlikely to exist, but do we need a reworded definition?
 
Volta said:
So if I bring the high-leg of a delta along for the ride, it is no longer a multiwire branch circuit?

Might be very unlikely to exist, but do we need a reworded definition?
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I'd say not. I think the only time you'd ever have all three phases and the neutral in a single run would beas a feeder.

Plus, any time the neutral is available where the high leg also is, the high leg must be orange.
 
tom baker said:
Did you look at the NEC definition of a MWBC?
I find it interesting that we know what something is until a new requirment costs us money. Examples:
Kitchens and GFCIs-what is a kitchen?
Vending machines and GFCIs-what is a vending machine?

I suspect MWBC are a thing of the past...
Click to expand...

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LarryFine said:
I'd say not. I think the only time you'd ever have all three phases and the neutral in a single run would beas a feeder.

Plus, any time the neutral is available where the high leg also is, the high leg must be orange.
Click to expand...
Sure, but

Don't underestimate the hacks!

2000 watt / 208 volt baseboard, 240 volt rated breaker.
Two 20 amp receptacle branches, 120/240 volt breakers.
One 12/4 with ground, red wire identified. You know, orange in color, if you like, or by other effective means.:grin:

Not saying it's good, but is it a multiwire branch circuit?
I don't think it is. The grounded conductor doesn't have an equal voltage between it and each ungrounded conductor of the circuit.
 
amptech said:
??????????????????????????
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He's saying (I think) for years, the NEC refused to define a kitchen. I know that may proposals were submitted to do so, but the CMP replied, "The definition of a kitchen is so well-known, there is no need for the NEC to define it."

Yet, today a kitchen is defined.

Vending machines also used to be exempt from GFI protection. Now they aren't. They also have gained NEC-defined status.
 
slick 50 said:
Even if it was a feeder it still requires the simultanious disconnect.
Click to expand...
Yes, but the question was whether the presence of the high leg affects whether a group of conductors is still a MWBC, and I'm saying it shouldn't ever matter.

I was saying that you wouldn't normally use such a group as a branch circuit. Ypu'd either use the three phases, or you'd use the two 120v lines and the neutral.
 
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