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So, I have a Square D QO panel that had one of the original AFCI breakers go bad, and in the process of researching how to fix that, I learned a bit about this whole AFCI thing and how newer code requires it in virtually all living areas. After replacing the bad breaker (test button never worked), this means that only my bedrooms have AFCI protection via two breakers. I began to look at my living room setup and discovered that it's on a two-pole breaker (15A), with the second pole shared by the main hallway and bathroom lighting circuit, w/ both branch circuits sharing the neutral wire.

Some more digging turns up that Square D (now owned by Schneider-Electric) does not make a two-pole AFCI breaker for QO panels, citing limited demand for two-pole AFCI for shared neutral circuits (pg 6). So I looked up an AFCI receptacle, which are pretty new overall, and found the AFTR1-W by Leviton. If I were to get and install such a receptacle as the first living room receptacle downstream of the living room breaker, will that provide AFCI protection for all downstream receptacles? And will the neutral wire going through the the living room circuit cause the AFCI receptacle to trip if I flipped on the hallway or bathroom lights?

If so, that will cover about 98% of my living room outlets. Oddly enough, it appears that the builders pigtailed somewhere after the living room breaker, but before the first receptacle, and used that pigtail to power a GFCI receptacle by my front door that grants GFCI protection to the receptacle outside on the front of the house. I can test this, because if I plug a GFCI tester into the first downstream socket, I can't trip the nearby GFCI receptacle, so they have to be in parallel somehow.

I don't think that if I put the AFCI receptacle in that I'll be able to cover that GFCI receptacle as well, unless I find the pigtail in the wall and wire it to be on the load side of the AFCI receptacle somehow. But that's only assuming the shared neutral doesn't prohibit me from even using the AFCI receptacle. Also doesn't look like they make a combination AFCI and GFCI receptacle device, either.

Also, Schneider-Electric has this to say about shared neutrals in residential wiring, too.

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Arc-Fault Circuit Interrupter (AFCI) receptacles are similar to Ground-Fault Circuit Interrupter (GFCI) receptacles, in that they both operate on the Line / Load idea. When connecting an AFCI receptacle, downstream devices are only protected if they are connected to the Load side of the device. If devices are connected in parallel using pigtails on the Line side, they will not be protected by the AFCI device.

Since connection-wise, AFCI and GFCI receptacles are similar. The answers to these questions can be useful in this situation as well.

Basically, these devices only monitor the wires on the Load side of the device. Which means, anything upstream on the Line side doesn't really matter. Sharing a neutral should not be a problem, as long as it's done properly (e.g. don't share a Load side neutral, only share the Line side neutral before the device).

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Let us also not forget, code changes are not required to be immediately implemented. Updating to current code standards is only required, when changes are made to the system. –  Tester101 Jun 12 '13 at 11:54
    
Aye, I went looking up what the current code it is that my county supports, because I last remember reading they supported 2005 NEC. The only language I can find now says they implement whatever is currently available. I don't know if that means they still have to officially adopt a particular code book at a meeting, or if it's a lazy way to keep up to date. Thanks for the tips on the GFCI wiring, too. I am still open to options that can be done at the panel instead of using an AFCI receptacle, but I definitely want to avoid having to re-wire both circuits. –  Kumba Jun 12 '13 at 21:32
    
That said, I did find this CH215CAF breaker by Eaton‌​, but I don't think that is compatible for QO load centers, so until Square D/SE releases something, my options at the panel appear to be very limited w/o rewiring those two circuits. I don't suppose it's allowed to use two single-pole AFCI breakers and pigtail their load-side neutrals, right? –  Kumba Jun 12 '13 at 21:37
    
Also to add, subpanels aren't a good option. The main panel is flush-mounted with a wall in the living room, so any new panels would require cutting holes in the wall and such. And I've got a window to the left of the main panel, and the corner of the house to the right, too. –  Kumba Jun 12 '13 at 21:39
    
The type of circuit you're talking about, is a multiwire branch circuit. It can indeed use two single pole breakers as the disconnecting means, as long as the breakers are connected using identified handle ties or a master handle (NEC 2008 225.33(B)). However, this would not be an option when dealing with AFCI or GFCI breakers. –  Tester101 Jun 13 '13 at 11:51
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I similarly had difficulty locating a 2-pole AFCI for a shared neutral circuit in a Cutler-Hammer box. My go-to elecrical supply wholesaler first had it on back-order, then when it didn't come in with his order, he called and was told it was discontinued. I consulted city inspector, who wanted more documentation than me saying it was discontinued. So then I checked with another wholesaler, who said "you just have to know how to order them." Don't know WHAT that meant, but he sold me one, and it works just fine.

So next time I would recommend to dig a little deeper (that pdf you cite is from 2002, when AFCIs were a rather new-fangled technology in many people's eyes), ask at multiple suppliers about whether anyone makes a compatible 2-pole AFCI. Call your local building inspector anonymously to see if they've seen other cases of unavailable 2-pole AFCIs. My inspector certainly didn't let on to having had it come up before, and so that was when I started calling around more.

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While a relevant observation, you don't really answer the question. This would be better as a comment. –  HerrBag Jun 29 '13 at 15:42
    
@Julie: I scoured through Square-D/Schneider-Electric's website looking for a 2-pole AFCI breaker for a QO load center and they simply don't have one. If it's not listed on the manufacturer's site, it likely doesn't exist. I later confirmed that the breaker currently in the panel is NOT sharing a neutral. It's using two runs of 14/2 romex, w/ only the black wires connected to the breaker's load screw and the two neutrals connected to the neutral bus bar. That said, the AFCI outlet has been tripping a couple of times, and I suspect my kitchen light is to blame, so, the adventure continues.. –  Kumba Jul 2 '13 at 22:28
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