AFCI required on MWBC?

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david luchini said:
I don't see anything in that text that says that the receptacle is rated for the "voltage class" 120/240.
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The UL text clearly states that the receptacle is rated for use split-wired on a MWBC with the ungrounded tab removed. The definition of "voltage, nominal" clearly states that 120/240 is a voltage class.

So the question just reduces to what voltage class to assign to an MWBC, 120, or 120/240? If the latter, then the UL text implies that the receptacle is rated for the "voltage class" 120/240.

Cheers, Wayne
 
kwired said:
How often is a 14-20 used in the rooms mentioned in 210.12?
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Not often, but I'm getting ready to install one in the "bedroom" that I use as my office/workroom. Actually, it might be a L14-30R since I think I already have that and a PDU that matches and that avoids the 15/20 amp thing altogether.


There's also that pesky "single phase" part of 210.12(A) which suggests, to me, that there is only one ungrounded lead. Because 3-phase is unlikely to be used in a dwelling unit at all, let along distributed to most rooms, it appears that the CMP was aiming at only 120v outlets and not those supplying 240/120.

I suspect that there are multiple opinions about that :lol:.
 
wwhitney said:
The UL text clearly states that the receptacle is rated for use split-wired on a MWBC with the ungrounded tab removed. The definition of "voltage, nominal" clearly states that 120/240 is a voltage class.

So the question just reduces to what voltage class to assign to an MWBC, 120, or 120/240? If the latter, then the UL text implies that the receptacle is rated for the "voltage class" 120/240.

Cheers, Wayne
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The receptacle is explicitly listed and marked with a 125V rating....not a 125/250V rating.

The UL text does not imply that the receptacle is rated for a voltage other than that which it explicitly listed and marked for.
 
jap said:
How can a strictly 120v circuit be a Multi Wire Branch Circuit when a strictly 120v circuit only requires 2 conductors?

If you do not have more than 2 conductors, then, there is no way possible you're dealing with a Multiwire Branch Circuit which is 2 ungrounded conductors that share a neutral.

JAP>
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jap said:
In fact, if you put your meter across any 2 conductors of a 120/240v 1ph or 120/208v 3ph Y branch circuit, and, the highest reading your getting is only 120 volts, then your not dealing with a MWBC at all. :)

Therefore, a multi-wire branch circuit is not a 120v circuit.


JAP>
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And then you repeated yourself that a multi-wire branch circuit is not a 120v circuit (because another "hot" conductor is involved) and you want to use that to skirt the AFC rules. I simply think you are wrong.
 
oldsparky52 said:
And then you repeated yourself that a multi-wire branch circuit is not a 120v circuit (because another "hot" conductor is involved) and you want to use that to skirt the AFC rules. I simply think you are wrong.
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I do not skirt AFCI rules.

You think I'm wrong because you simply don't know any better.

If you think a 120v circuit is a multiwire branch circuit, or, that a multiwire branch circuit is 120v, however you want to say it, you're sadly mistaken.

A 120v circuit can however be a PART of a multiwire circuit, and a PART of a 120/240v circuit, but, not a 120v circuit by itself.

JAP>
 
wwhitney said:
Because sometimes it is only one circuit, e.g. 225.30. And 210.4(A) provides the option to look at it either way.

Cheers, Wayne
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But what does that have to do with running a 3-wire MWBC for two 120 volt circuits in a location that requires AFCI protection?
 
If you look at 210.4(C), you will see that MWBCs shall supply only line to neutral loads. Then there are 2 exceptions to look at it otherwise.

The point is, it starts out by definition as multiple 120v circuits, period. Then you can modify it.

To say a MWBC is not a 120v circuit is in my opinion, wrong.
 
infinity said:
But what does that have to do with running a 3-wire MWBC for two 120 volt circuits in a location that requires AFCI protection?
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Let's say I run 12/3 to a series of split wired duplex receptacles with the ungrounded tabs removed. Is that really two 120V circuits? Or one 120/240V circuit?

[I think the simplest solution to the conflict here is to declare that a 120/240V circuit is also a 120V circuit, so 210.12 applies.]

Cheers, Wayne
 
And let's not forget, until not too long ago, the breakers for a MWBC could be anywhere in the panel. How can you have (1) circuit that has to be shut off in multiple locations in the panel?

I think most of us agree the handle tie rule came about because of the lack of understanding in how to safely share a neutral by people sticking their fingers where they don't belong.

MWBC's traditionally and mostly are 120v circuits.
 
wwhitney said:
Let's say I run 12/3 to a series of split wired duplex receptacles with the ungrounded tabs removed. Is that really two 120V circuits? Or one 120/240V circuit?

[I think the simplest solution to the conflict here is to declare that a 120/240V circuit is also a 120V circuit, so 210.12 applies.]

Cheers, Wayne
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Yes it's two circuits because once you remove the tab it's two separate receptacles.
 
Cheers, Wayne[/QUOTE]

wwhitney said:
UL RTRT guideinfo says in part "Duplex receptacles rated 15 and 20 A that are provided with break-off tabs may have those tabs removed so that the two receptacles may be wired in a multi-wire branch circuit or multiple branch circuits."

So a duplex receptacle seems to be rated for the "voltage class" 120/240.

Cheers, Wayne
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wwhitney said:
The UL text clearly states that the receptacle is rated for use split-wired on a MWBC with the ungrounded tab removed.

Cheers, Wayne
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Cheers, Wayne[/QUOTE]

wwhitney said:
UL RTRT guideinfo may have those tabs removed so that the two receptacles may be wired in a multi-wire branch circuit or multiple branch circuits."

Cheers, Wayne
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I can break the ungrounded tap on a single 120 volt circuit to make a switch un -switch rec in a dinning room

It may be common practice to do the same on a multi- wire circuit but the standard you posted seems to say break off tabs that would make a duplex two single rec
 
wwhitney said:
Let's say I run 12/3 to a series of split wired duplex receptacles with the ungrounded tabs removed. Is that really two 120V circuits? Or one 120/240V circuit?
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I say it's two 120v circuits, and a duplex so wired is two 120v receptacles. No single plug can access both ungrounded conductors.
 
infinity said:
A 3-wire MWBC is two 120 volt circuits. Why is that so hard to understand?

Yes it's two circuits because once you remove the tab it's two separate receptacles.
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Agree. And that's why a split-wired duplex is still a 120v device.
 
oldsparky52 said:
I think most of us agree the handle tie rule came about because of the lack of understanding in how to safely share a neutral by people sticking their fingers where they don't belong.
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Especially when using tandems. They seem to confuse people.

MWBC's traditionally and mostly are 120v circuits.
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Agree. Otherwise, it's just a 120/240v circuit with a neutral.
 
oldsparky52 said:
If you look at 210.4(C), you will see that MWBCs shall supply only line to neutral loads. Then there are 2 exceptions to look at it otherwise.

The point is, it starts out by definition as multiple 120v circuits, period. Then you can modify it.

To say a MWBC is not a 120v circuit is in my opinion, wrong.
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If You go to the supply house and buy just enough black, white,and green the length you need for a 120v circuit, you will not have enough wire for a multi wire branch circuit because you will be missing the 2nd ungrounded conductor to make it a MWBC.

Why is this so difficult for you to understand?

Jap>
 
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