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Old 04-06-2010, 05:00 PM   #1
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AFCI vs MWBC


I'm in the process of swapping out my old FPE panel for a new Homeline. I'm trying to stick to NEC 2008 standards while doing this (no permits/inspections where I live). However, I'm having a problem with using AFCI breakers for the master bedroom suite, since the suite is powered by two circuits on a MWBC.

I cannot find a double-pole AFCI breaker for Homeline. I know I could install two single-pole AFCI's, but I don't want to deal with finding handle jumpers (if they even make them for AFCI's). For now, I'm planning to use a regular double-pole 15A breaker.

Any suggestions?

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Old 04-06-2010, 05:03 PM   #2
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AFCI vs MWBC


You cannot use single pole AFCIs on multiwire branch circuits.

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Old 04-06-2010, 08:33 PM   #3
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AFCI vs MWBC


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You cannot use single pole AFCIs on multiwire branch circuits.
Great, that suits my preference. So......... How does one comply with ACFI requirements when using MWBC's??
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Old 04-06-2010, 09:07 PM   #4
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We don't do it very often for this very reason. When we do we use 2 pole AFCIs. Siemens brand.
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Old 04-06-2010, 09:40 PM   #5
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We don't do it very often for this very reason. When we do we use 2 pole AFCIs. Siemens brand.
Rats. If I'd known I'd face this issue, I would have gone with a Siemens panel.

However, given my S-D Homeline panel is purchased and partially installed already, guess I'll just have to go without AFCI for now.

Thanks for the helpful feedback, Brric.

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Old 04-06-2010, 10:16 PM   #6
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AFCI vs MWBC


gotta love it when the coder requires something that is not available.

I don't know if the have the needed breaker but Cutler Hammer tends to certify their breakers in any panel they actually fit in. I would have to do some looking to see it there is a CH AFCI breaker that fits and is listed. Maybe one of the guys that do resi all the time would know offhand.
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Old 04-06-2010, 11:02 PM   #7
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AFCI vs MWBC


Is it possible to re-run the wire and make it a full blow two circuit room rather than MWBC using shared neutrals?
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Old 04-07-2010, 01:38 AM   #8
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Is it possible to re-run the wire and make it a full blow two circuit room rather than MWBC using shared neutrals?
Not any time soon. The master suite makes up the partial 2nd floor, and is wired from above in the attic. I haven't climbed up to that part of the attic yet, due to difficulty to access. I need to do some duct work there, as well as some rewiring for a ceiling fan, so I'll make it there eventually.

....No, really, I will.
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Old 04-07-2010, 01:58 AM   #9
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Not any time soon. The master suite makes up the partial 2nd floor, and is wired from above in the attic. I haven't climbed up to that part of the attic yet, due to difficulty to access. I need to do some duct work there, as well as some rewiring for a ceiling fan, so I'll make it there eventually.

....No, really, I will.
I've got a volumous attic area with lots of odd shapes (lots of different types of high ceilings, some strait up, some vaulted, odd angles). I basically had to install some ladders and catwalk made from 2x4s and plywood to allow me easy access to the full attic.
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Old 04-07-2010, 02:09 AM   #10
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Originally Posted by Itsdanf View Post
I know I could install two single-pole AFCI's, but I don't want to deal with finding handle jumpers (if they even make them for AFCI's).
If you have QO breakers, square D does make "handle tie".
http://www.drillspot.com/products/50...THT_Handle_Tie
http://www.drillspot.com/products/49...1HT_Handle_Tie

(Note: Links posted to show samples of the product. I don't know anything about this retailer, just one of the first that popped up on a google search for square d handle ties.)
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Old 04-07-2010, 02:25 AM   #11
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Originally Posted by HooKooDooKu View Post
If you have QO breakers, square D does make "handle tie".
http://www.drillspot.com/products/50...THT_Handle_Tie
http://www.drillspot.com/products/49...1HT_Handle_Tie

(Note: Links posted to show samples of the product. I don't know anything about this retailer, just one of the first that popped up on a google search for square d handle ties.)
Thanks for checking. I've got HOM, not QO.

What I'm planning to do for now is use a 2-pole breaker for this MWBC. I'll look at singe-pole AFCI's if/when I can convert the MWBC to two fully-separate circuits.
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Old 04-07-2010, 07:38 AM   #12
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I'd see if The cutler-hammer CH double-pole AFCI fits your panel like Nap suggested, since these are bedrooms.
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Old 04-07-2010, 09:37 AM   #13
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If your thought was that by handle tying 2 single pole afci's together makes it a double pole afci you are mistaken. Not sure if that is what you meant but just wanting to let you know this will not work on a MWBC.

Brric mentioned this in post #4
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Old 04-07-2010, 10:42 AM   #14
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Originally Posted by secutanudu View Post
I'd see if The cutler-hammer CH double-pole AFCI fits your panel like Nap suggested, since these are bedrooms.
POCO's coming tomorrow to shut down the power. I'm scrambling to get everything ready, so no more time to research for now. I'll look into it next week (easy enough to swap out the breakers then).

Thanks all for the feedback!
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Old 04-07-2010, 11:37 AM   #15
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If your thought was that by handle tying 2 single pole afci's together makes it a double pole afci you are mistaken. Not sure if that is what you meant but just wanting to let you know this will not work on a MWBC.
OK, the lightbulb (for me at least) just came on...

So for the benefit of anyone else reading this and asking "why not?":

With an AFCI breaker, both the hot AND neutral is connected to the AFCI breaker, with the breaker having a pigtail that connects to the neutral bar. For the AFCI to work properly, you've got to have your circuit neutral connected to the AFCI neutral. But if you've got two AFCI breakers trying to service a MWBC, you've only got one neutral comming back to two AFCIs.

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