Alternatives for AFCI for a 15/20 MWBC (Multi-wire Branch Circuit)

[wwhitney]

I'd tend to agree if the MWBC originated inside. The OP said the breakers were located outside and supplied an apartment, the sole supply.

In the OP's case, it's likely an apartment building with the supply to the apartment originiating from equipment mounted on the outside of the building. So Article 225 would not apply.

But then post #15 raised the idea of using an asymmetric MWBC for a detached garage, in which case Article 225 would apply. Still, there is no problem with an asymmetric MWBC there, either. 225.30 says "For the purpose of this section, a multiwire branch circuit shall be considered a single circuit. " You left out the first part in your quote. So 225.30 is not requiring you to consider an MWBC a single circuit for any other sections.

That means you can consider the MWBC a single circuit for 225.30, while considering it multiple circuits for 210.18. No contradiction.

Cheers, Wayne

 

[pipe_bender]

In the OP's case, it's likely an apartment building with the supply to the apartment originiating from equipment mounted on the outside of the building. So Article 225 would not apply.

The way I read 225.1 it says article 225 covers any outside branch circuits and feeders run on buildings.

 

[wwhitney]

The way I read 225.1 it say article 225 covers any outside branch circuits and feeders run on buildings.

OK, I agree that Article 225 may have requirements for wiring on the outside of a building, I have not reviewed the whole article to check.

But in the context of 225.30, supplying a building means bringing power to it from a point not in or on the building. 225.30 does not apply to wiring that originates at one point in or on a building and terminates in another point in or on a building.

Cheers, Wayne

 

[wwhitney]

A local gas company's gas separation rule means we have to re-feed the branch circuits to a new location more than 6 wire feet away.

So the panel shown in post #9 is outside near the gas meter, and there are no breakers within the apartment? And you have to move that outside panel, which requires extending the branch circuit(s) by more than 6 feet? [Note that my reading of 210.12(E) Exception is that you can shorten the branch circuits by any desired amount under the exception, as any negative number is less than 6.]

What are the options here?

Just double checking that you understand that post #2 has the answer. Your new panel in the new location could be a 2 space outdoor Siemens or GE panel (or apparently either Eaton BR or Eaton CH, although a quick google did not tell me which one), with a 15A single pole AFCI and a 20A single pole AFCI, handle-tied. Those AFCI breakers (per Don's post) do not require a neutral connection, you can land the MWBC neutral on the neutral bar as usual.

Just curious, I assume there must be conduit running to each apartment? As I wouldn't think you'd find a cable wiring method with 2 #12s, 1 #14, and a #12 EGC.

Cheers, Wayne

 

[curt swartz]

So the panel shown in post #9 is outside near the gas meter, and there are no breakers within the apartment? And you have to move that outside panel, which requires extending the branch circuit(s) by more than 6 feet? [Note that my reading of 210.12(E) Exception is that you can shorten the branch circuits by any desired amount under the exception, as any negative number is less than 6.]


Just double checking that you understand that post #2 has the answer. Your new panel in the new location could be a 2 space outdoor Siemens or GE panel (or apparently either Eaton BR or Eaton CH, although a quick google did not tell me which one), with a 15A single pole AFCI and a 20A single pole AFCI, handle-tied. Those AFCI breakers (per Don's post) do not require a neutral connection, you can land the MWBC neutral on the neutral bar as usual.

Just curious, I assume there must be conduit running to each apartment? As I wouldn't think you'd find a cable wiring method with 2 #12s, 1 #14, and a #12 EGC.

Cheers, Wayne

I believe CH still has GF protection. Both SquareD QO and HOM also have GF protection.

You would not need a hybrid cable. 12/3 and use 1 #12 wire for the 15 amp circuit.

 

[wwhitney]

You would not need a hybrid cable. 12/3 and use 1 #12 wire for the 15 amp circuit.

Ah, with one leg needing to be protected at 15A because within the dwelling unit it supplies #14. Agreed that's more likely.

Cheers, Wayne

 

[Joe Villani]

Did you Look at the abb (old GE) line of AFCIs

They use handle ties and single pole breakers.

 

[pipe_bender]

But in the context of 225.30, supplying a building means bringing power to it from a point not in or on the building. 225.30 does not apply to wiring that originates at one point in or on a building and terminates in another point in or on a building.

I am not seeing where 225.30 differentiates in that way.

 

[wwhitney]

I am not seeing where 225.30 differentiates in that way.

If you're going to apply 225.30 to wiring that is wholly on or within a building, then you can only have one branch circuit in the building, which is nonsensical. So it is implicit that 225.30 applies to wiring where one end is not on or in the building, and the other end is on or in the building. That's the usual notion of what it means to "supply" a building.

Also, the second paragraph discusses feeder or branch circuits between two different buildings. Which fits with the idea that "supply" means "supply from a point not in or on the building."

That's all I got, it's not spelled out but it's obviously the intention.

Cheers, Wayne

 

[pipe_bender]

If you're going to apply 225.30 to wiring that is wholly on or within a building, then you can only have one branch circuit in the building, which is nonsensical.

To me 225.30 is saying each independent firewall separated dwelling has to be feed from one feeder or branch circuit, but perhaps I have been reading that 225.1 wrong.
I guess I have just never seen a dwelling supplied by a 15/20 multi wire branch circuit, is that something you regularly did or saw as an EC there before you retired? Is this a California thing?

 

[wwhitney]

To me 225.30 is saying each independent firewall separated dwelling has to be feed from one feeder or branch circuit

Oh, that I agree with, but that's because true firewalls create separate "buildings" per the NEC's definition of building. So if you have a structure divided into multiple buildings with true firewalls, and the service equipment is on one of those buildings, and a different building is supplied from that service, it would need to comply with 225.30, even though it's all one structure.

But an apartment building doesn't generally have true firewalls. The fire rated separation between apartments is not a firewall. A firewall per the building code is literally a wall for which the structure on one side could catch fire and burn down without any effect on the structure on the other side. E.g. a properly detailed concrete block wall from a foundation slab straight up to and through the roof, with zero penetrations of any type.

Anyway, as I noted at the beginning of the day, even if 225.30 does apply to this asymmetric MWBC to the apartment, it's fine for the MWBC to be one circuit for the purposes of 225.30 and two circuits for the purposes of 210.18.

Cheers, Wayne