Shared neutrals and "individual branch circuits"

[tls]

New York City amends the 2005 code with:

"Subsection 210.11(C)(4) - Add a new subsection 210.11(C)(4) to read as follows:

(4) Air-Conditioning Branch Circuit. In addition to the number of branch circuits required by other parts of this section, an individual branch circuit shall be provided for each air-conditioning receptacle required by 210.52(I)."

This requirement dates back to prior to New York City's adoption of the NEC, though I don't know if the "individual branch circuit" wording was in the old NYC code. I've seen these wired as MWBC with a shared neutral on 12/3 BX from the panel to the first A/C outlet at the perimeter of the building literally hundreds of times. Obviously the current on the neutral won't exceed 20A (assume typical NYC 2-phase apartment wiring) so this is certainly safe.

I'm told inspectors are starting to reject these even in modifications to existing work (e.g. where a 2-pole AFCI breaker turns out to be required in a new panel) because a MWBC doesn't fall under the definition of "individual branch circuit". I can see the point. And I assume it's possible, even likely (since 120/208 is so common here) that the drafters of the NYC amendments wanted to avoid 20A on the BX armor due to a bad neutral splice at the first J-box or receptacle... but, in practice, what a pain.

The cheapest general fix seems like it might be a subpanel fed by the original 12-3. But where there are, say, 8 existing air conditioners in a large apartment, and this objection comes up -- oof. 4 new 2-space panels.

Opinions?

 

[infinity]

Here's the NEC definition of Branch Circuit, Individual. Where does it say separate neutral?

Branch Circuit, Individual. A branch circuit that supplies only one utilization equipment.

 

[LarryFine]

. . . a MWBC doesn't fall under the definition of "individual branch circuit".

I disagree with that assessment.

And I assume it's possible, even likely ... that the drafters of the NYC amendments wanted to avoid 20A on the BX armor due to a bad neutral splice at the first J-box or receptacle...

Why would an open neutral place any current on an EGC or metallic sheath?

 

[charlie b]

Although I will not say (not yet, anyway) that I disagree with Rob and Larry, the situation is not all that clear to me. The “C” word in “MWBC” is generally written and spoken in the singular. It is a single circuit. But I can serve three receptacles from a 3-phase MWBC, with a separate ungrounded conductor run to each of the three receptacles. That would give me a single circuit that serves more than one utilization equipment. How does that fit the definition of “individual branch circuit”?

 

[charlie b]

To me previous post I will add that I think I understand the intent of the local code, and I think that allowing a MWBC does not detract from the ability of the system to meet that intent. All I addressed was the wording of the two definitions.

I think it would be appropriate to offer a proposed change to the local code (if they even entertain such proposals).

 

[LarryFine]

... I can serve three receptacles from a 3-phase MWBC, with a separate ungrounded conductor run to each of the three receptacles. That would give me a single circuit that serves more than one utilization equipment. How does that fit the definition of ?individual branch circuit??

I'm under the impression that a MWBC can be considered one circuit or three. After all, one circuit wouldn't be supplied by three 1p breakers.

 

[charlie b]

I'm under the impression that a MWBC can be considered one circuit or three.

Good point! Perhaps the second sentence of 210.4(A) might be the basis for arguing in favor of allowing a MWBC in this application. It says that "A multiwire branch circuit shall be permitted to be considered as multiple circuits." Thus, each of the "multiple circuits" can supply one duplex receptacle and nothing else, and thus each would count as an "individual branch circuit."

 

[infinity]

Good point! Perhaps the second sentence of 210.4(A) might be the basis for arguing in favor of allowing a MWBC in this application. It says that "A multiwire branch circuit shall be permitted to be considered as multiple circuits." Thus, each of the "multiple circuits" can supply one duplex receptacle and nothing else, and thus each would count as an "individual branch circuit."

Can it supply a duplex or would it have to be a single receptacle?

 

[dbuckley]

Possibly the intent was to avoid lights flickering as the A/C cycles, so having a MWBC (or indeed a 2 space panel on the end of a only-just-adequate-for-the-load feeder) is countrary to that intent?