AFCI required on MWBC?

[wwhitney]

Verifying compliance with the voltage rating of the subset of the branch circuit is verifying compliance with the voltage rating of the branch circuit.

That is certainly not true for an MWBC, as the Voltage rating of the full Branch Circuit differs from the Voltage rating of the subset consisting of one ungrounded conductor and the neutral.

Cheers, Wayne

 

[wwhitney]

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

The sentence you quoted said that the wiring is part of a 120V circuit.

Cheers, Wayne

 

[jap]

The sentence you quoted said that the wiring is part of a 120V circuit.

Cheers, Wayne

The wiring of a MWBC is either "Part" of a 120/240v beginning, or, is "Part" of a 277/480v beginning.

None of the wiring of a MWBC is "Part" of a 120v beginning or "Part" of a 277v beginning.

Jap>

 

[david luchini]

That is certainly not true for an MWBC, as the Voltage rating of the full Branch Circuit differs from the Voltage rating of the subset consisting of one ungrounded conductor and the neutral.

Cheers, Wayne

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.

You seem to be ignoring "A multiwire branch circuit shall be permitted to be considered as multiple circuits." To comply with the requirements of the installation of the receptacle outlets, the wiring is part of multiple 120V branch circuits

 

[oldsparky52]

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.

Again, if you read 210.4(C) without the exceptions, you will see that you are mistaken. You are only correct if you use an exception. Therefore, a MWBC is by 210.3(C) line to neutral connections.

A MWBC that has 240v connected loads is an exception to the rule.

 

[jap]

Again, if you read 210.4(C) without the exceptions, you will see that you are mistaken. You are only correct if you use an exception. Therefore, a MWBC is by 210.3(C) line to neutral connections.

A MWBC that has 240v connected loads is an exception to the rule.

210.4C states a Multiwire branch circuits shall "Supply" only line-to-neutral loads barring the exceptions, not that the MWBC is line to neutral connections.

If MWBC's were simply line to neutral connections, we could call every 120v circuit a MWBC, which we all know they are not.

JAP>

 

[wwhitney]

You seem to be ignoring "A multiwire branch circuit shall be permitted to be considered as multiple circuits." To comply with the requirements of the installation of the receptacle outlets, the wiring is part of multiple 120V branch circuits

The sentence you just quoted uses the phrase "multiple circuits", not "multiple Branch Circuits". That's why my statement used the phrase "120V circuits", not "120V Branch Circuits."

Cheers, Wayne

 

[oldsparky52]

210.4C states a Multiwire branch circuits shall "Supply" only line-to-neutral loads barring the exceptions, not that the MWBC is line to neutral connections.

If MWBC's were simply line to neutral connections, we could call every 120v circuit a MWBC, which we all know they are not.

JAP>

You are being obtuse. You win, I quit. I don't agree, but you seem to be trolling.

 

[david luchini]

The sentence you just quoted uses the phrase "multiple circuits", not "multiple Branch Circuits". That's why my statement used the phrase "120V circuits", not "120V Branch Circuits."

Cheers, Wayne

Are those circuits between the final overcurrent device protecting the circuit and the outlet(s)?

If it's a multi-wire Branch Circuit, how could it multiple anything else except Branch Circuits?

 

[jap]

You are being obtuse. You win, I quit. I don't agree, but you seem to be trolling.

Well that's an improvement.

At least now you and I've progressed from a blunt " I think you're wrong" like in post #53 to a more civil "I don't agree", 95 posts later.

Heck, a few more posts and I might just overlook the, drinking, smoking, obtuse, trolling comments also.



Thanks,

JAP>

 

[wwhitney]

If it's a multi-wire Branch Circuit, how could it multiple anything else except Branch Circuits?

This gets back to our disagreement about whether a proper subset of a Branch Circuit is a Branch Circuit. I say no, so the word circuit is used to refer to the 2-wire subsets of the MWBC.

If the code writers meant multiple Branch Circuits, why did they leave out the word branch? Based on the consistency of this omission and the omissions in 210.6 and 406.4, I believe the omissions are intentional.

Cheers, Wayne

 

[LarryFine]

The bottom line is that a MWBC is made up of multiple single circuits, and each of those must follow the rules.

 

[david luchini]

This gets back to our disagreement about whether a proper subset of a Branch Circuit is a Branch Circuit. I say no, so the word circuit is used to refer to the 2-wire subsets of the MWBC.

If the code writers meant multiple Branch Circuits, why did they leave out the word branch? Based on the consistency of this omission and the omissions in 210.6 and 406.4, I believe the omissions are intentional.

Cheers, Wayne

I don't have any disagreement about subsets of branch circuits, as there are no subsets of branch circuits...only branch circuits. I don't believe "subset" is in the Code anywhere.

Why would the Code writers have to use the redundant word "branch" every time they are referring to branch circuits? If they tell you that receptacle outlets SHALL BE INSTALLED on branch circuits, and then go on to use only "circuits" in reference to voltage class of the circuits that receptacles are installed on, it's because "branch" is completely redundant. SHALL BE INSTALLED ON BRANCH CIRCUITS means SHALL BE INSTALLED ON BRANCH CIRCUITS, not shall be installed on some mystery circuit that is not a branch circuit.

 

[oldsparky52]

Well that's an improvement.

At least now you and I've progressed from a blunt " I think you're wrong" like in post #53 to a more civil "I don't agree", 95 posts later.

Heck, a few more posts and I might just overlook the, drinking, smoking, obtuse, trolling comments also.



Thanks,

JAP>

Well, :lol: I do think you are wrong. A MWBC is not a 240v circuit. It is more than 1 120v circuits sharing a neutral. If you do what the exceptions allow, you may use it as a 120/240v circuit. And yes, a MWBC requires AFC when AFC's are called for. If you are just serving 240v loads, it's not a MWBC, it's a 240v circuit.

 

[wwhitney]

Why would the Code writers have to use the redundant word "branch" every time they are referring to branch circuits?

Fine, that's how you see it, and so you read the word "circuit" as "Branch Circuit" in this case.

I, on the other hand, see a fairly consistent usage of the term "circuit" instead of Branch Circuit in various NEC sections relating to Voltage rating, and I attribute that to the fact that the Voltage rating of a Multi-Wire Branch Circuit does not match the Voltage rating of some of its 2-wire subcircuits.

Cheers, Wayne

 

[wwhitney]

A MWBC is not a 240v circuit.

To repeat what's been quoted before, the Article 100 definitions tell us otherwise:

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

Voltage (of a circuit). The greatest root-mean-square (rms) (effective) difference of potential between any two conductors of the circuit concerned.

Thus

- a MWBC on a 120/240V system consists of two ungrounded conductors plus the neutral
- the three pairwise voltages between those three conductors are 120V, 120V, and 240V
- the greatest value is 240V
- so the Voltage of the MWBC is 240V.

Cheers, Wayne

 

[oldsparky52]

Thus

- a MWBC on a 120/240V system consists of two ungrounded conductors plus the neutral
- the three pairwise voltages between those three conductors are 120V, 120V, and 240V
- the greatest value is 240V
- so the Voltage of the MWBC is 240V.

Cheers, Wayne

No, a MWBC is multiple 120v circuits sharing a neutral (no more than 1 per phase). You may use it as a 120/240v circuit if you follow the exceptions. 210.4(C) explains that yet you ignore it. :happysad:

 

[wwhitney]

No, a MWBC is multiple 120v circuits sharing a neutral (no more than 1 per phase). You may use it as a 120/240v circuit if you follow the exceptions. 210.4(C) explains that yet you ignore it. :happysad:

I gave a proof above that the Voltage rating is 240V per the NEC definitions. Which step do you disagree with? If none, please accept the result and put aside your preconceived notions.

Cheers, Wayne

 

[david luchini]

Fine, that's how you see it, and so you read the word "circuit" as "Branch Circuit" in this case.

I, on the other hand, see a fairly consistent usage of the term "circuit" instead of Branch Circuit in various NEC sections relating to Voltage rating, and I attribute that to the fact that the Voltage rating of a Multi-Wire Branch Circuit does not match the Voltage rating of some of its 2-wire subcircuits.

Cheers, Wayne

You continue to ignore 406.4. Receptacle outlets aren't allowed to be installed on "subcircuits"...another made up term that isn't in the Code...they are only allowed to be installed on branch circuits.

You are trying to make an argument on how to violate 406.4.

The Code is clear on what SHALL means with respect to Code rules.

 

[wwhitney]

You continue to ignore 406.4.

I do not ignore 406.4. The portion of 406.4 that refers to voltage rating uses the term "circuit" instead of "Branch Circuit", just like 210.6 does, and 210.4(A) does. These sections are all consistent in this regard.

Cheers, Wayne