AFCI required on MWBC?

[wwhitney]

I don't see anything in that text that says that the receptacle is rated for the "voltage class" 120/240.

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

 

[zbang]

How often is a 14-20 used in the rooms mentioned in 210.12?

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:.

 

[david luchini]

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

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.

 

[oldsparky52]

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>

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>

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.

 

[jap]

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.

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>

 

[infinity]

A 3-wire MWBC is two 120 volt circuits. Why is that so hard to understand?

 

[wwhitney]

A 3-wire MWBC is two 120 volt circuits. Why is that so hard to understand?

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

 

[infinity]

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

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?

 

[oldsparky52]

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.

 

[wwhitney]

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?

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

 

[oldsparky52]

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.

 

[oldsparky52]

[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.]

:thumbsup:

 

[infinity]

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

Yes it's two circuits because once you remove the tab it's two separate receptacles.

 

[david]

Cheers, Wayne[/QUOTE]

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

The UL text clearly states that the receptacle is rated for use split-wired on a MWBC with the ungrounded tab removed.

Cheers, Wayne

Cheers, Wayne[/QUOTE]

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

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

 

[LarryFine]

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 say it's two 120v circuits, and a duplex so wired is two 120v receptacles. No single plug can access both ungrounded conductors.

 

[LarryFine]

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.

Agree. And that's why a split-wired duplex is still a 120v device.

 

[LarryFine]

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.

Especially when using tandems. They seem to confuse people.

MWBC's traditionally and mostly are 120v circuits.

Agree. Otherwise, it's just a 120/240v circuit with a neutral.

 

[infinity]

Agree. And that's why a split-wired duplex is still a 120v device.

Yup, you end up with two single 120 volt receptacles on one yoke.

 

[jap]

A 3-wire MWBC is two 120 volt circuits. Why is that so hard to understand?

Good for you infinity.

I think you're finally getting it.

Jap>

 

[jap]

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.

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>