AFCI required on MWBC?

[wwhitney]

Would you care to point out the NEC definition of "circuit", especially as contrasted to "branch circuit"? It doesn't exist.

That's right, it doesn't exist. Your reading adds the word "branch" in front of circuit willy-nilly. As a first draft, I would say a circuit is "some conductors going to and from an Outlet".

Are you saying a branch circuit is not a circuit? A feeder is not a circuit? A control circuit is not a circuit?

Those are all circuits. And the fact that a Feeder is a circuit shows you can't just substitute "Branch Circuit" every time you read the word circuit.

404.6 tells you that a receptacle SHALL BE INSTALLED in a branch circuit. 404.6(A) tells you a grounding type receptacle SHALL BE INSTALLED in a circuit of the same voltage class as the receptacle. There is no gray area there.

The gray area is that the second requirement does not use the phrase "Branch Circuit". So is the word "circuit" there just shorthand for "Branch Circuit"? That seems to be your reading. Or is the requirement just saying that the voltage supplied to the receptacle has to match the receptacle's rating? That's my reading, and that depends only on the part of the circuit the receptacle is connected to, not the rating of the Branch Circuit as a whole.

Again the undefined term "circuit" is a more flexible word than the defined term "Branch Circuit".

Cheers, Wayne

 

[wwhitney]

All branch circuits are circuits, but not all circuits are branch circuits? :?

Right. All red cars are cars, but not all cars are red cars.

Cheers, Wayne

 

[jap]

(I thought I posted something like this yesterday, but apparently it didn't upload...)

[MENTION=56260]david luchini[/MENTION] has given the most robust answer to my original question. The MWBC is a 240V circuit per Article 100. But 210.4 permits it to be 'considered as' two 120V circuits. If it is being 'considered as' to meet a code requirement (such as 404.6) then the arc fault requirement will then kick in. (Everyone else who has who just blankly asserted that the MWBC is two circuits was not adequately addressing my original question.)

I still think the language of 210.12 is not crystal clear.

So by the very first sentence above that makes the most sense,

A MWBC is not a 120v circuit?

Hmmmmm...... what was I thinking?

Jap>

 

[david]

So by the very first sentence above that makes the most sense,

A MWBC is not a 120v circuit?

Hmmmmm...... what was I thinking?

Jap>

i do not see a multi wire branch circuit as intended to be a 240 volt circuit

i see the flexibility as it being considered a single branch circuit as in a building being supplied by one branch circuit

or an allowance to consider it as two branch circuits for the purpose of meeting a requirement in an area that has a min requirement to be served by two circuits

or loading a branch circuit with rec that have to be given a 180 VA rating

If you have a multi wire circuit serving an appliance such as a range originating from a two pole breaker that circuit being a branch circuit would have a 240 volt rating. There is no allowance to consider a multi wire range branch circuit as two individual branch circuits

A code defined multi wire branch circuit has an allowance to be supplied by single pole breakers

Would you ever think it code compliant to supply a 240 volt multi wire branch circuit with single pole breakers.

It is however done all the time with code defined multi wire branch circuits and the answer is because a code defined multi wire branch circuit by design is a 120 volt branch circuit

 

[david]

i do not see a multi wire branch circuit as intended to be a 240 volt circuit

i see the flexibility as it being considered a single branch circuit as in a building being supplied by one branch circuit

or an allowance to consider it as two branch circuits for the purpose of meeting a requirement in an area that has a min requirement to be served by two circuits

or loading a branch circuit with rec that have to be given a 180 VA rating

If you have a multi wire circuit serving an appliance such as a range originating from a two pole breaker that circuit being a branch circuit would have a 240 volt rating. There is no allowance to consider a multi wire range branch circuit as two individual branch circuits

A code defined multi wire branch circuit has an allowance to be supplied by single pole breakers

Would you ever think it code compliant to supply a 240 volt multi wire branch circuit with single pole breakers.

It is however done all the time with code defined multi wire branch circuits and the answer is because a code defined multi wire branch circuit by design is a 120 volt branch circuit

I am talking about multi wire branch circuits being discussed in this thread the ones the code gives an allowance to be considered two circuits

 

[jap]

I am talking about multi wire branch circuits being discussed in this thread the ones the code gives an allowance to be considered two circuits

Without more than 1 ungrounded conductors there is no MWBC to begin with.


Jap>

 

[david luchini]

That's right, it doesn't exist. Your reading adds the word "branch" in front of circuit willy-nilly. As a first draft, I would say a circuit is "some conductors going to and from an Outlet".

I haven't read the word "branch" in front of circuit willy-nilly. The Code has told me, in multiple locations, that the circuit is a branch circuit.

Those are all circuits. And the fact that a Feeder is a circuit shows you can't just substitute "Branch Circuit" every time you read the word circuit.

This is a strawman argument, which is as weak an argument as making up your own Code terms. No one has suggested substituting branch circuit every time you read the word circuit. Fortunately for us, the Code provides definitions of Branch Circuit and Feeder so that we can tell the difference between the two.

Even more fortunately for us, 406.4 tells us TWICE before it gets to "circuits of the voltage class and current for which they are rated" that the circuits are Branch Circuits.

The gray area is that the second requirement does not use the phrase "Branch Circuit". So is the word "circuit" there just shorthand for "Branch Circuit"? That seems to be your reading. Or is the requirement just saying that the voltage supplied to the receptacle has to match the receptacle's rating? That's my reading, and that depends only on the part of the circuit the receptacle is connected to, not the rating of the Branch Circuit as a whole.

There is no gray area...406.4(A) says grounding type receptacles SHALL BE INSTALLED ONLY ON CIRCUITS OF THE VOLTAGE CLASS AND CURRENT for which they are rated. If the voltage rating of the receptacle is 125V, and the circuit is 240V, then the receptacle cannot be installed on that circuit. If the receptacle is rated for 20A, and the circuit is 30A, then the receptacle cannot be installed on that circuit.

 

[kwired]

Only that a MWBC is not a 120v circuit,or that a 120v circuit is not a MWBC. The circuit would have to have more than only 1 120v circuit to be a MWBC, otherwise there would not be one. K-wire Picked up on it when he stated 120/240v 120/208v or 277/480v. We do a lot of reading between the line where we're from.

Right, MWBC is not a single voltage, and certainly isn't limited to something with 120 volts involved, 120 is pretty popular voltage to be involved though.

The question the OP asked is:

Is a multi-wire branch circuit a '120-volt' circuit?


I guess we'll just let him believe that it is.


JAP>

If anything (and has sort of been addressed) 120 volt based MWBC's are at least treated as equivalent to two individual 120 volt branch circuits in many ways.

I mentioned possible loophole for AFCI's as food for thought more so than a statement that there actually is any loophole. I certainly did not research this hard enough to make a definite statement there is indeed a loophole. As complex as it can get to interpret everything in the code as well as how hard it can be to write code that doesn't have unintended situations here and there, there very well could be an unintended loophole in there.

To say a MWBC is not a 120v circuit is in my opinion, wrong.

A MWBC can be 277/480 or other possible combinations that don't involve 120. 120 just happens to be about the most common utilization voltage of a MWBC, and 277 volts probably second most common utilization voltage of a MWBC.

Add: seems there were many posts I hadn't yet read before making this post, only skimmed over them after posting this sorry if I addressed something in those posts. I did want to state my mentioning of AFCI loophole was primarily an attempt to get people thinking that the possibility of unintended loophole may be there and to make their own conclusions or even come up with public input if something is discovered that needs changed to clarify.

 

[wwhitney]

which is as weak an argument as making up your own Code terms.

I've not made up any Code terms, I've just pointed out the difference between a defined term and an undefined term.

Even more fortunately for us, 406.4 tells us TWICE before it gets to "circuits of the voltage class and current for which they are rated" that the circuits are Branch Circuits.

So your position, as I understand it, is that when the code section uses the term Branch Circuit twice, that means any further use of the term circuit in that section really means Branch Circuit. Whereas I would say "hmm, why did they change terminology? There is a difference being communicated here."

I think we'll have to agree to disagree on this point. Both of our positions follow logically depending on the above interpretation.

If the voltage rating of the receptacle is 125V, and the circuit is 240V, then the receptacle cannot be installed on that circuit.

Certainly I agree with this. The disagreement is about the scope of the word "circuit" in that requirement.

Cheers, Wayne

 

[david luchini]

I've not made up any Code terms, I've just pointed out the difference between a defined term and an undefined term.

Sure you did. You made up the terms "local circuit" and "smaller circuit" to try to avoid saying that the receptacle outlets were on a branch circuit.

So your position, as I understand it, is that when the code section uses the term Branch Circuit twice, that means any further use of the term circuit in that section really means Branch Circuit. Whereas I would say "hmm, why did they change terminology? There is a difference being communicated here."

No, my position is that when the Code tells you that the receptacle outlets are required to be installed on branch circuits, and then goes on to say that grounding-type receptacles are required to be installed on circuits of the voltage class and current for which they are rated, the Code has already told us that the "circuit" is a "branch circuit." It's not exactly rocket science.

The term "circuit" is used rather than "branch circuit" dozens of times in Article 210 Branch Circuits. Do you believe that the Code is using the term circuit to mean something other than branch circuit in those instances?
The requirements for Dwelling Unit Receptacles are provided in section 210.52 in Article 210 Branch Circuits. Do you believe that the Code is not telling you that receptacle outlets in dwelling units are not to be installed on branch circuits? The definition of Branch Circuit tells you that it is the circuit conductors between the final overcurrent to device protecting the circuit and the outlet(s). Do you really believe that a receptacle outlet installed on circuit conductors which are between the final overcurrent device protecting the circuit and that outlet are not installed on a branch circuit? Section 406.4 tells you that receptacle outlet shall be located in branch circuits. Do you really believe that receptacle outlet can be installed in a circuit which is not a branch circuit?

The Code practically beats you over the head telling you that receptacles are installed in branch circuits, but you will ignore all of that to "interpret" the circuits as being something else? All to avoid providing the require arc-fault protection?

 

[wwhitney]

Sure you did. You made up the terms "local circuit" and "smaller circuit" to try to avoid saying that the receptacle outlets were on a branch circuit.

I used those phrases before my current capitalization policy, but those were just "local circuit" and "smaller circuit," not "Local Circuit" or "Smaller Circuit". Not code terms, just a way of referring to a circuit that is a strict subset of a Branch Circuit.

Cheers, Wayne

 

[LarryFine]

I'm sure we can tell the difference between a 120/240v circuit that supplies a single load and one that supplies 120v general-purpose receptacles. If a 120v circuit is required to have AFCI protection, I don't see how that changes because a shared neutral is used in the supply.

The only difference between a 3-wire MWBC and two individual 2-wire BCs is that the neutrals split at the point the MWBC becomes two BCs on the former and they "split" on the neutral bus on the latter. What does that have to do with whether each circuit needs AFCi protection?

The AFCI requirement is based on the locations and other characteristics of the loads of the circuit, not on how it got there.

 

[david luchini]

I used those phrases before my current capitalization policy, but those were just "local circuit" and "smaller circuit," not "Local Circuit" or "Smaller Circuit". Not code terms, just a way of referring to a circuit that is a strict subset of a Branch Circuit.

Cheers, Wayne

Well, there you have it. All of the elements in set A which is a subset of set B, are also elements of set B. The elements of a subset of a branch circuit are elements of a branch circuit.

Any receptacles outlets that are installed on a portion, or a subset, of a branch circuit are installed on a branch circuit, and must meet the requirements for branch circuits.

 

[wwhitney]

The term "circuit" is used rather than "branch circuit" dozens of times in Article 210 Branch Circuits. Do you believe that the Code is using the term circuit to mean something other than branch circuit in those instances?

Yes. It is a more flexible term that may mean the whole Branch Circuit, or a portion of it, or a Feeder plus a Branch Circuit, etc.

Take a look at 210.6, another section about the Voltage rating of circuits. The subsections all use the word circuit, not Branch Circuit. It is the first significant cluster within Article 210 of the bare word circuit, rather than Branch Circuit. 210.4 also uses the word circuit when referring to considering an MWBC as multiple circuits.

So why are all of these sections consistently using the term circuit rather than Branch Circuit? It corresponds with the definition of "Voltage (of a circuit)" in Article 100. For a 120/240V MWBC, the rating of the Branch Circuit is 240V per that definition. Under 210.4, the MWBC may also be considered two circuits, which are rated 120V per the definition. 210.6 only cares about the Voltage rating of the circuits, not of the whole Branch Circuit. Therefore the subsections in 210.6 use the term circuit, rather than Branch Circuit.

Again, an MWBC on a 120/240V system is a Branch Circuit rated at 240V, and it comprises two 120V circuits, which may supply 120V Outlets.

Cheers, Wayne

 

[wwhitney]

Well, there you have it. All of the elements in set A which is a subset of set B, are also elements of set B. The elements of a subset of a branch circuit are elements of a branch circuit.

Any receptacles outlets that are installed on a portion, or a subset, of a branch circuit are installed on a branch circuit, and must meet the requirements for branch circuits.

I agree with the above. But the requirement in question is not worded in terms of Branch Circuits, it is worded in terms of a circuit. So we can take a subset of the Branch Circuit and use its Voltage rating in order to demonstrate compliance with 406.4 (or 210.6).

Cheers, Wayne

 

[david luchini]

I agree with the above. But the requirement in question is not worded in terms of Branch Circuits, it is worded in terms of a circuit. So we can take a subset of the Branch Circuit and use its Voltage rating in order to demonstrate compliance with 406.4 (or 210.6).

Cheers, Wayne

The subset of the branch circuit is a branch circuit. Verifying compliance with the voltage rating of the subset of the branch circuit is verifying compliance with the voltage rating of the branch circuit. Having verified voltage compliance of the branch circuit, I think you will find it is a circuit of the voltage and current rating that required Arc-Fault protection in dwelling units.

 

[david luchini]

Again, an MWBC on a 120/240V system is a Branch Circuit rated at 240V, and it comprises two 120V circuits, which may supply 120V Outlets.

Those two 120V circuits are 120V branch circuits however you look at it. You would not be able to supply receptacle outlets from those circuits if they are not branch circuits. It's as simple as that.

 

[wwhitney]

Those two 120V circuits are 120V branch circuits however you look at it. You would not be able to supply receptacle outlets from those circuits if they are not branch circuits. It's as simple as that.

The wiring is both part of a 240V Branch Circuit and part of a 120V circuit. So that satisfies the requirement that a 125V Receptacle be located on a Branch Circuit and be supplied by a 120V circuit.

Cheers, Wayne

 

[wwhitney]

The subset of the branch circuit is a branch circuit.

We disagree. A proper subset of a Branch Circuit is not a Branch Circuit, per the wording of the definition.

Cheers, Wayne

 

[jap]

The wiring is both part of a 240V Branch Circuit and part of a 120V circuit. So that satisfies the requirement that a 125V Receptacle be located on a Branch Circuit and be supplied by a 120V circuit.

Cheers, Wayne

To my knowledge, there is no voltage that is "Part" of a 120v circuit.

JAP>