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Old 12-09-2009, 01:14 PM   #1
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Afci & 12/2


Hi all. Been a 'lurker' for years, but now find myself needing to ask a question.

Refinishing basement and ran 2 20A GFCI circuits using 12/2 (w/ground) with 4 outlets on each circuit, none switch controlled. I was on the cusp of my municipality's change from 2005 to 2008 NEC but technically fall under 2005. Because of considerations related to the mechanical room, I initially didn't think this space was going to qualify as a bedroom. After I ran my 12/2 and wired my outlets, and after speaking with code technicians, I found that I could get it counted as a bedroom, one of the caveats being that the outlets had to be AFCI protected.

So I switched out the GFCI breakers with AFCI in my Square D panel. Now I'm getting random "nuisance trips" while using higher draw things like saws, regardless of which outlet I use, and w/no other loads on the circuit. Everything worked fine while the GFCIs were installed and a GFCI plug in tester gave me green lights across the board.

Do I need to do something special with the neutral at the terminating outlet? I'll pull out each outlet and make sure there's no unintentional contact and that there's no undue lack of insulation where the wire connects to each outlet, but what else am I missing here? Can't seem to find one one the web...can anyone point me to a wiring diagram for proper AFCI wiring of multiple outlets?

Thanks in advance for any thoughts.

P.S. - As a side note, this is in Colorado and on the days I've happened to have been working and had these trips, it's been very cold. It was -17F outside when I started work this morning. Could the cold be contracting the copper in the panel and have anything to do with it?

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Last edited by golddog; 12-09-2009 at 01:36 PM.
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Old 12-09-2009, 01:20 PM   #2
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Afci & 12/2


Did you wire the neutral to the breaker, and the built-in pigtail to the neutral buss?

I would not think the cold should have any effect.

The title says 12-3, but you said 2 runs of 12-2. Could you clarify?

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Old 12-09-2009, 01:38 PM   #3
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Just saw the title mistake and corrected it. It's 12/2.

I did wire the neutral and the pigtail. It was a tight fit to get them in there so I'll make sure they're cranked down good and tight and didn't come loose during the process of shoehorning them in there.

Last edited by golddog; 12-09-2009 at 01:45 PM.
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Old 12-09-2009, 02:32 PM   #4
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Afci & 12/2


Quick update: Pulled the tripping breaker (I haven't gone live with the 2nd circuit) reseated it and made sure all the connections were nice and tight (they were). Mitre saw tripped the breaker on my 2nd cut. If it helps, the breaker is a Square D 20A single pole model HOM12CAFIC. So unless the breaker itself is bad, and I know I'm not overloading the circuit, there's got to be an arc fault in there somewhere right? But speaking of bad breakers, if I can run a radio and a shop-vac for 20 minutes on the same outlet that trips with the saw, wouldn't that point to a bad breaker rather than a fault somewhere?
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Old 12-09-2009, 02:45 PM   #5
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I have read in a few places that anything with a motor (power tool, refrigerator, vaccuum) can inherently cause nuisance AFCI trips. It may very well be wired fine, and that your saw will never operate on an AFCI without tripping it.
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Old 12-09-2009, 04:09 PM   #6
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What color is the button on the GFCI ?
Square D had a recall on some
Green button is the newer AFCI, older was blue - but not all blue were bad

http://www.squared.com/us/squared/co...llFrameset.htm
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Old 12-09-2009, 04:53 PM   #7
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http://www.google.com/search?hl=en&c..._nhi=&safe=off

Mike Holt's official position may be that these things are 'not ready for prime time.'
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Old 12-09-2009, 08:52 PM   #8
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Quote:
Originally Posted by Scuba_Dave View Post
What color is the button on the GFCI ?
Square D had a recall on some
Green button is the newer AFCI, older was blue - but not all blue were bad

http://www.squared.com/us/squared/co...llFrameset.htm
The button is actually white...not sure what that means. Surrender?

The more I think about it, this has to be wired correctly. I've been playing around with different loads and it works fine until something with a big motor gets online (as secutanudu and Google point out). Mind you these are not things that are overloading the circuit in the traditional sense of the word.I can pull the trigger on the mitre saw, leave it running and no trip; actually try to cut some wood and put the motor under some stress and it trips. If there were a true arc fault it would trip no matter how many amps I was pulling down right?
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Old 12-09-2009, 08:56 PM   #9
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Afci & 12/2


I have 2 older lamps that work fine on every circuit except AFCI
Possibly an older socket that is detectable by the AFCI when turn on - thinks it is a spark
Some Vacs can also cause a problem
Brushes in some saws may trip it also

I don't think they are quite ready yet for wide user
But they passed into code
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Old 12-10-2009, 11:14 AM   #10
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Quote:
Originally Posted by golddog View Post
I can pull the trigger on the mitre saw, leave it running and no trip; actually try to cut some wood and put the motor under some stress and it trips. If there were a true arc fault it would trip no matter how many amps I was pulling down right?
The arc voltage depends on the motor inductance, the current drawn and how many times the current is interrupted per second.
Loading down the motor increases the current drawn and may change the arc characteristics so it goes from being judged a good arc to being judged a bad arc.

There may also be arc characteristics shared by both good arcs and bad arcs, and if so, this technology will never completely work right.
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Old 12-10-2009, 12:09 PM   #11
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Quote:
Originally Posted by Yoyizit View Post
The arc voltage depends on the motor inductance, the current drawn and how many times the current is interrupted per second.
Loading down the motor increases the current drawn and may change the arc characteristics so it goes from being judged a good arc to being judged a bad arc.

There may also be arc characteristics shared by both good arcs and bad arcs, and if so, this technology will never completely work right.
Thanks yoyizit. That actually makes sense. This, and a different thread in here about a computer UPS and AFCI got me thinking. Tucked away in a corner on the same circuit, I had my old Dewalt 14.4v battery charger plugged in, always with a spare in it. I also happen to have usually had an old transistor radio on while I'm working. I've noticed that when the charger is active, it creates a large amount of distinct line noises for the radio...the only thing out of all my gadgets to do so. I unplugged the charger from the circuit and presto, no more nuisance trips with the saws. The charger only draws 2A but there must be something about its cycle that freaks out the AFCI.

Resolution of this issue aside, and with all due respect this part of the code and its intent, as soon as I get my CO I'm replacing these w/regular breakers. When I go to sell the house I'll swap them back in and let someone else figure it out. Maybe by then they'll have AFCI v2.0.
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Old 12-10-2009, 12:23 PM   #12
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Actually I think they are on at least AFCI v3.0

Glad you figured it out
Hopefully it will help others who may have a problem

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