AFCIs on a 220v circuit, sort of

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I had run a 12/3 w.g 220v circuit to my attic, and then branched into two 12/2 w.g to run 110v to each of two separate GFCI-protected wall outlets. Originally I had a ganged double pole 20a 220v breaker supplying this paired circuit, and all was well. And the electrical inspector was content.
But then a different electrical inspector told me that instead i needed to have AFCI breakers in the breaker box, since these outlets are in bedrooms. So, I bought two 20a AFCIs (I could find no double pole 220v AFCIs and the guy at HomeDepot said with this situation they should have been on two separate breakers anyway.)
Well, now the AFCIs trip (both of them simultaneously) whenever there is any load on either circuit. My guess is that because there is a shared neutral, the AFCIs are getting confused. But I am also wondering if the problem might be because there are GFCIs at each outlet. Can GFCIs and AFCIs cooexist okay? If so, then is there a way to use AFCIs in this situation?
Thanks for your help.
emichaelb
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AFCI contains a 30mA GFCI. You cannot use GFCI with a shared neutral. It wants to see equal current on the neutral and the hot. With a shared neutral, there is no way to make it work. Like you said, the GFCI (within the AFCI) is confused.
If you want AFCI, you need to have two 12/2 circuits. In the future perhaps someone would make AFCI receptacles you can installed in the bedroom, or double AFCI breaker specifically for shared neutral ciruit.
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thanks.
hmm, then I just have to remove the afci breakers and revert to a standard breaker I guess. Was the HomeDepot fellow right that this should have two unganged breakers, one for each circuit? That would make me nervous - if one trips or is turned off, there is still current in that calbe on the other circuit.
emichael
peter wrote:

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It's fine, just make sure your common neutral connections are pigtailed and not dependent on the receptacles

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They are in fact pigtailed, btu why is it okay to have current in one circuit in the romex ? Is that not a hazard to someone who thinks the power is off by having thrown one breaker?
And altho you are saying it IS legal to have two unganged breakers, is it not okay (or even better) to do it with a ganged 220 v breaker like I had it before and like the first inspector passed on?
emichael
RBM wrote:

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You actually have two separate circuits. With circuit A off, all the outlets etc attached are dead. With circuit B off, all those outlets are dead. The only problem or danger is in unsplicing the common neutral. By connecting the two circuits to a double pole breaker, you eliminate that possible danger as well. I don't recall code on when a double pole is required for Edison circuits, but I believe if outlets in one box are connected to both live legs, you're required to use a double pole breaker

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I understand. thanks.
emichael
RBM wrote:

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Linked breakers required only on the same yoke (strap), not just in the same box.
NEC 210.4 B (2005) (B) Devices or Equipment. Where a multiwire branch circuit supplies more than one device or equipment on the same yoke, a means shall be provided to disconnect simultaneously
all ungrounded conductors supplying those devices or equipment at the point where the branch circuit originates.
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Sounds logical to me. Thanks.
emichael
Paul A wrote:

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[That only applies to the NEC. The CEC _requires_ tied breakers on shared neutral circuits, period.]
But that's irrelevant. The original issue is NOT whether the breakers are tied together, but because they share a neutral.
You _cannot_ feed a shared neutral circuit with two separate AFCI's or GFCI's. It just don't work. Code or not.
You either have to split the neutral (run another cable), OR, install the AFCI's AFTER the circuit splits to the bedrooms.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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thanks.
emichael
RBM wrote:

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You are correct that you can't share a neutral between the two breakers. You need to run separate two wire circuits to the bedrooms. Why are you installing GFCI outlets in bedrooms?

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These are for window AirConditioners, and happen to be right next to hot water radiators, which I figured are as likely to be as good a ground as a faucet in a bathroom.
Do you see any reason that I cannot simply use the ganged 220v breaker like I had it before (ignoring the AFCI for now.) That way both circuits are tripped when either one is overloaded.
emichael
RBM wrote:

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Not a problem

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thanks so much.
btw, in the future if I decide to use my now useless AFCIs in two new kitchen circuits, would a GFCI be needed at the outlets? Or are AFCIs doing both jobs according to code?
emichael
RBM wrote:

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AFCI's are for bedrooms only, kitchen's require GFCI's for all counter outlets

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okay thanks.
emichael
RBM wrote:

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The GFCI inside the AFCI trips at 30mA. It is meant to protect equipments, not human. I believe this GFCI is an unpublicized feature of AFCI. Therefore you still need to install a regular GFCI, which trips at 5mA.
In the future there will be combination AFCI/GFCI (trips at 5mA). This is puzzling to me. If they have a built-in 30mA GFCI, it should cost very little to make it trip at 5mA, and they can sell it for more.
BTW, current AFCI only detects parallel fault (e.g. an intermitent short circuit). They will be required to detect series arc as well (intermittent open circuit) eventually.
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Thanks for letting me know the details of these GFCIs.
emichael
peter wrote:

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No offense, but reading some of the replies, you need to leave this group, and get yourself a licensed and insured electrician, before you kill someone. Or worse, void your home insurance policy! :D
later,
tom
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