AFCI required on MWBC?

[wwhitney]

In what jurisdictions have they agreed with you? Is it okay for me to call them?

I'm refining my argument here in this thread, then I'll run it past my inspector and see what he says.

I think the intent of 210.12 is for the requirement to apply to MWBCs supplying 120V utilization equipment, they just haven't been very careful with the language.

Cheers, Wayne

 

[wwhitney]

I say that the load connections, as well as the source, defines the circuit.

What matters for applying 210.12 is the "branch circuit" and its rating.

Cheers, Wayne

 

[david luchini]

Let's look at the definition of branch circuit:



Your interpretation would be correct if the definition started out "Any portion of the circuit conductors . . ."

However, the definition does not say that. So the "branch circuit" is all of the 12/3 cable circuit conductors in my example, starting at the 2p 20 amp breaker. There is one branch circuit, comprising the entirety of those circuit conductors. The "branch circuit" is reducible into a sum of smaller circuits, but those smaller circuits are not branch circuits.

Cheers, Wayne

The "smaller circuits" conductors that you are describing are literally circuit conductors between the final overcurrent device protecting the circuit and the outlets...the exact definition of "branch circuit."

If you have to make up terms that aren't in the NEC, such as "local circuits" and "smaller circuits," to make your argument, it's probably a good bet that your argument is wrong.

Now read 406.4, as further evidence that your argument is wrong.

 

[david luchini]

What matters for applying 210.12 is the "branch circuit" and its rating.

This is correct...and the branch circuits that the 125V, 15A or 20A receptacles required in dwelling units are installed in are rated at 15A, 120V or 20A, 120V. Those receptacles are not allowed to be installed on any other branch circuit.

 

[wwhitney]

The "smaller circuits" conductors that you are describing are literally circuit conductors between the final overcurrent device protecting the circuit and the outlets...the exact definition of "branch circuit."

For clarity in this thread, I'm going to start capitalizing terms defined in Article 100 (I may miss some, but those definitions aren't really critical to the discussion).

With "smaller circuits" I'm not attempting to make up a new defined term, I'm just talking about a circuit that is less than the full Branch Circuit.

The crux of our disagreement is whether an incomplete part of a Branch Circuit is itself a Branch Circuit, or whether it is just a circuit. I'm reading the definition of "Branch Circuit" to mean the entire Branch Circuit; if you just take an incomplete part of it, you have a circuit, you have circuit conductors, it is made up of Branch Circuit conductors, but it is not by itself a Branch Circuit.

210.12 refers to the rating of the Branch Circuit. So you have to consider all the Branch Circuit conductors when determining the Voltage of the Branch Circuit. The definition of Voltage (Of A Circuit) makes it clear the MWBC in my example has a Voltage of 240V. That means 210.12 doesn't apply.

The requirement in 406.4(A) you've been referring to reads "grounding-type receptacles shall be installed only on circuits of the voltage class and current for which they are rated," and it does not use the term Branch Circuit. It uses the term circuit, which can be a small portion of a Branch Circuit. So again, the 240V Branch Circuit supplies a 120V circuit that supplies the receptacle. No 406.4(A) violation.

I don't see any other way to reconcile the definitions without reaching a contradiction.

Cheers, Wayne

 

[jap]

For clarity in this thread, I'm going to start capitalizing terms defined in Article 100 (I may miss some, but those definitions aren't really critical to the discussion).

With "smaller circuits" I'm not attempting to make up a new defined term, I'm just talking about a circuit that is less than the full Branch Circuit.

The crux of our disagreement is whether an incomplete part of a Branch Circuit is itself a Branch Circuit, or whether it is just a circuit. I'm reading the definition of "Branch Circuit" to mean the entire Branch Circuit; if you just take an incomplete part of it, you have a circuit, you have circuit conductors, it is made up of Branch Circuit conductors, but it is not by itself a Branch Circuit.

210.12 refers to the rating of the Branch Circuit. So you have to consider all the Branch Circuit conductors when determining the Voltage of the Branch Circuit. The definition of Voltage (Of A Circuit) makes it clear the MWBC in my example has a Voltage of 240V. That means 210.12 doesn't apply.

The requirement in 406.4(A) you've been referring to reads "grounding-type receptacles shall be installed only on circuits of the voltage class and current for which they are rated," and it does not use the term Branch Circuit. It uses the term circuit, which can be a small portion of a Branch Circuit. So again, the 240V Branch Circuit supplies a 120V circuit that supplies the receptacle. No 406.4(A) violation.

I don't see any other way to reconcile the definitions without reaching a contradiction.

Cheers, Wayne

How bout we just install an AFCI on our MWBC's if we need to and be done with it .

Jap>

 

[david luchini]

For clarity in this thread, I'm going to start capitalizing terms defined in Article 100 (I may miss some, but those definitions aren't really critical to the discussion).

With "smaller circuits" I'm not attempting to make up a new defined term, I'm just talking about a circuit that is less than the full Branch Circuit.

The crux of our disagreement is whether an incomplete part of a Branch Circuit is itself a Branch Circuit, or whether it is just a circuit. I'm reading the definition of "Branch Circuit" to mean the entire Branch Circuit; if you just take an incomplete part of it, you have a circuit, you have circuit conductors, it is made up of Branch Circuit conductors, but it is not by itself a Branch Circuit.

You're still making up terms to try to make your argument. There is no such Code thing as "less than a full branch circuit" or "incomplete part of a branch circuit.".

210.12 refers to the rating of the Branch Circuit. So you have to consider all the Branch Circuit conductors when determining the Voltage of the Branch Circuit. The definition of Voltage (Of A Circuit) makes it clear the MWBC in my example has a Voltage of 240V. That means 210.12 doesn't apply.

This is still wrong. Code does NOT allow you to install 125V receptacles on a 240V branch circuits. This means you either cannot use a mwbc to supply the required residential receptacles, or you can use the Code permission to consider the mwbc multiple circuits (specifically two 120V circuits in this example.)

The requirement in 406.4(A) you've been referring to reads "grounding-type receptacles shall be installed only on circuits of the voltage class and current for which they are rated," and it does not use the term Branch Circuit. It uses the term circuit, which can be a small portion of a Branch Circuit. So again, the 240V Branch Circuit supplies a 120V circuit that supplies the receptacle. No 406.4(A) violation.

You seem to be again arguing that the receptacles aren't installed in a branch circuit, but some other circuit supplied by a branch circuit. Aside from the the obvious contradiction to the definition of branch circuit for this approach, it is clear that you didn't read the reference that I gave to 406.4. Receptacles must be installed in a branch circuit. To argue that the branch circuit is 240V and the 120V circuit is something other than a branch circuit would be to argue for a violation of 406.4.

I don't see any other way to reconcile the definitions without reaching a contradiction.

There is no contradiction in the definitions. You only need follow all of the related Code requirements for a proper installation.

 

[jaggedben]

...
Code does NOT allow you to install 125V receptacles on a 240V branch circuits. ...

You've stated this three times without citing any code section to back it up. I think it's wrong. Clearly 125V receptacles may be installed on a 120/240V multiwire branch circuit. Article 100 makes clear that the voltage of this branch circuit is 240.

 

[wwhitney]

First, I would like to reiterate that the term "circuit" in the NEC is a different term than Branch Circuit. Circuit is not defined in Article 100. That is why I say a circuit may be part of a branch circuit, or a part of a feeder, or some combination of the above. In applying the sections discussed here, we need to pay attention to when the term circuit is used, and when the term Branch Circuit is used.

- The article 100 definition of Branch Circuit means that in my example, the Branch Circuit is all 3 circuit conductors, the two ungrounded conductors and the neutral.

- 210.4(A) tells us that this MWBC may be considered two circuits (not two Branch Circuits). One circuit is one ungrounded conductor plus the neutral; the other is the other ungrounded conductor plus the neutral.

- The definition of Voltage (of a circuit) tells us how to assign voltage ratings to this single Branch Circuit and the associated 2-wire circuits. The Branch Circuit is rated at 240V, and the associated 2-wire circuits are rated at 120V.

- The 1st sentence of 406.4 tells us the receptacle must be located on a Branch Circuit (without reference to its rating). 406.4(A) tells us it must be located on a 120V circuit (not Branch Circuit), so as you say we appeal to 210.4(A) to consider the MWBC as two 120V circuits.

- 210.12 refers only to the Branch Circuit, which is rated 240V.

Cheers, Wayne

 

[david luchini]

You've stated this three times without citing any code section to back it up. I think it's wrong. Clearly 125V receptacles may be installed on a 120/240V multiwire branch circuit. Article 100 makes clear that the voltage of this branch circuit is 240.

I've cited the Code section to back it up on multiple occasions. 406.4(A). You cannot install a 125V receptacle on a 240V circuit.

The code makes it clear that a mwbc is permitted to be considered multiple branch circuits...in the common residential case, two 120V branch circuits. You can install 125V receptacles on the two 120V branch circuits.

 

[david luchini]

- The article 100 definition of Branch Circuit means that in my example, the Branch Circuit is all 3 circuit conductors, the two ungrounded conductors and the neutral.

The article 100 definition of Branch Circuit means all conductors which are installed between the final ocpd protecting the circuit and the outlets

- 210.4(A) tells us that this MWBC may be considered two circuits (not two Branch Circuits). One circuit is one ungrounded conductor plus the neutral; the other is the other ungrounded conductor plus the neutral.

Article 210 is for "branch circuits.". The "bc" in mwbc is for "branch circuit.". The two circuits you just described are by definition "branch circuits."

- The definition of Voltage (of a circuit) tells us how to assign voltage ratings to this single Branch Circuit and the associated 2-wire circuits. The Branch Circuit is rated at 240V, and the associated 2-wire circuits are rated at 120V.

The associated 2-wire circuits are 120V Branch Circuits. You would not be able to connect receptacles to them if they were not branch circuits.

- The 1st sentence of 406.4 tells us the receptacle must be located on a Branch Circuit (without reference to its rating). 406.4(A) tells us it must be located on a 120V circuit (not Branch Circuit), so as you say we appeal to 210.4(A) to consider the MWBC as two 120V circuits.

You are still not reading what 406.4 and 404.6(A) say. 404.6(A) literally uses the term Branch Circuit.

- 210.12 refers only to the Branch Circuit, which is rated 240V.

The branch circuits on which the 125V receptacles are installed are rated 120V. That is why AFCI protection is required.

 

[wwhitney]

The article 100 definition of Branch Circuit means all conductors which are installed between the final ocpd protecting the circuit and the outlets

Correct. And less than all the conductors would not be a Branch Circuit.

Article 210 is for "branch circuits.". The "bc" in mwbc is for "branch circuit.". The two circuits you just described are by definition "branch circuits."

In the case of two separate breakers with a handle tie, I agree, as there are two separate OCPDs. But with a single double pole breaker, the 2-wire circuits are not Branch Circuits.

You are still not reading what 406.4 and 404.6(A) say. 404.6(A) literally uses the term Branch Circuit.

It does in the first sentence, but that places no restriction on voltage. In the second sentence pertaining to "voltage class", the term used is circuit, not Branch Circuit.

I would agree with your analysis if you can show me that the word circuit should be read to be the term Branch Circuit. Otherwise, a careful reading of the sections under discussion proceeds as in my last post.

Cheers,
Wayne

 

[LarryFine]

In the case of two separate breakers with a handle tie, I agree, as there are two separate OCPDs. But with a single double pole breaker, the 2-wire circuits are not Branch Circuits.

How about a slight adjustment to this train of thought: When or why you would use two tied 1p breakers vs. one 2p gives us a clue to the puzzle:

Two 120v circuits that share a neutral would be compliantly supplied by a tied pair of 1p breakers, telling us that they are indeed two 120v circuits.

A single 240v circuit with neutral, used to supply 240v load(s) and/or receptacle(s), requires a 2p breaker, telling us that it is indeed a 240v circuit.

 

[tortuga]

How about a slight adjustment to this train of thought: When or why you would use two tied 1p breakers vs. one 2p gives us a clue to the puzzle:

Two 120v circuits that share a neutral would be compliantly supplied by a tied pair of 1p breakers, telling us that they are indeed two 120v circuits.

A single 240v circuit with neutral, used to supply 240v load(s) and/or receptacle(s), requires a 2p breaker, telling us that it is indeed a 240v circuit.

Interesting discussion, that is an excellent point.
Jap: they recommend drinking 8 glasses of water a day. As long as you wire the mwbc correct you wont smoke.

 

[jap]

Interesting discussion, that is an excellent point.
Jap: they recommend drinking 8 glasses of water a day. As long as you wire the mwbc correct you wont smoke.

Oldsparky must be very healthy then.


Jap>

 

[jap]

I'd drink more but I'm busy chasing my tail.


Jap

 

[david luchini]

Correct. And less than all the conductors would not be a Branch Circuit.

No it wouldn't. Since you cannot connect a receptacle to all of the conductors between the final ocpd and the outlets, it would be impossible to connect a receptacle to a branch circuit by your definition.

In the case of two separate breakers with a handle tie, I agree, as there are two separate OCPDs. But with a single double pole breaker, the 2-wire circuits are not Branch Circuits.

By this line of thought, it would not be possible to use a 2 pole breaker to supply the mwbc.

It does in the first sentence, but that places no restriction on voltage. In the second sentence pertaining to "voltage class", the term used is circuit, not Branch Circuit.

It has already told you in the first sentence, as you have just pointed out, the the "circuit" is a "branch circuit.". The receptacles can only be connected to a branch circuit.

I would agree with your analysis if you can show me that the word circuit should be read to be the term Branch Circuit. Otherwise, a careful reading of the sections under discussion proceeds as in my last post.

Cheers,
Wayne

Would you care to point out the NEC definition of "circuit", especially as contrasted to "branch circuit"? It doesn't exist. Are you saying a branch circuit is not a circuit? A feeder is not a circuit? A control circuit is not a 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.

 

[david]

Correct.

I would agree with your analysis if you can show me that the word circuit should be read to be the term Branch Circuit. Otherwise, a careful reading of the sections under discussion proceeds as in my last post.

Cheers,
Wayne

That too is back words you would have to show that term circuit in article 210 means something other than branch circuit

210.1 Scope.
This article covers branch circuits except for branch circuits that supply only motor loads, which are covered in Article 430. Provisions of this article and Article 430 apply to branch circuits with combination loads.

"The requirement for grouping shall not apply if the circuit enters from a cable or raceway unique to the circuit that makes the grouping obvious"


The term circuit is used throughout article 210 to mean branch circuit we cannot just choice to change the meaning of the word for our own purpose

 

[LarryFine]

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

 

[jaggedben]

(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.