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mhops 08-01-2009 11:36 AM

AFCI and 3-wire circuits...ugghh
Hi everyone-

Thanks to all who have contributed to this forum -- I have used your threads to help me along with my basement finishing project. I have run into a problem now that I have not been able to solve through any reading - hope there is help out there - here goes!

I just finished wiring 7 different circuits (it's a big basement) and hooked up the new breakers yesterday (I have a Siemens panel, btw). I am required to use AFCI breakers on all except the bathroom. Fine, did that (wired properly with circuit neutral and hot into the breaker, breaker pigtail into the neutral bus bar). Powered it on and tested my lighting circuits. For a few minutes, things worked great, all switches and lights worked as planned (several three-way switches). Then my pride turned sour as the breakers kept on tripping after a few seconds to minutes. A little searching and reading taught me that my problem is almost certainly using single-pole AFCI breakers on circuits with three-wire configurations.

Here is a representative example of one of my problem circuits:

AFCI Breaker -- 14/2 wire -- Single pole switch -- 14/3 wire -- 4 consecutive lights -- 14/2 wire -- Three-way switch -- 14/3 wire -- 1 Light (with 5 additional lights wired with 14/2 off of this) -- 14/3 wire -- Three-way switch

(In the box housing the first three-way switch I have 14/2 wire branching off to power 3 different single lights with single pole switches)

I understand how AFCI breakers work and why the one on this circuit is tripping -- the neutral wire is sometimes not neutral at all and the breaker thinks there is an arc. I also understand that there are double pole AFCI breakers out there, but I'm not sure how that would work, or if that is even the answer. Wouldn't connecting a red wire into one of the 2 neutral ports on the breaker would just cause the breaker to trip as this wire would sometimes just as hot as the black (just like the sometimes-neutral white wire)?

Is my wiring schematic bad? It would seem like this would otherwise be a VERY common situation (given the 2008 NEC requirements for AFCIs) and it seems like I should have found either a huge row of double pole AFCIs at the home store, or lots of talk about this situation online (code requires three-way light switch applications, and thus 14/3 in certain - common - places) How could you wire circuits with multiples sets of independently controlled lights and three-way switches without using 14/3? Or am I just not understanding how to wire AFCI breakers...

Any help is appreciated!



jbfan 08-01-2009 11:44 AM

Using 14/3 for the 3 way switches is not the reason the afci is tripping.
You used 14/2 from the breaker, which is proper.
Somewhere in the circuit, you have a staple driven to deep, or a neutral and ground touching in a fixture or switch.

After rereading the post, why did you run 14/3 into the fixtures?

mhops 08-01-2009 12:01 PM

Thanks, jbfan, for replying.

I ran the 14/3 wire so that I could switch on that first set of 4 lights (via the red wire) without affecting the downstream sets of lights. It would seem to me (and that may be saying something) that if I only used 14/2 wire, then the downstream lights would be switched on/off every time that first set was switched. The other use of 14/3 wire was allow three-way switching.

I really hope you are right about your first comments, that would seem much, much easier to fix.

kbsparky 08-01-2009 12:15 PM

First, determine whether you have a bad breaker, or bad wiring:

Try swapping out the offending AFI breaker with another one on a different circuit.

Does the tripping problem now occur on the alternate circuit, or does the same circuit trip out with the different breaker?

mhops 08-01-2009 12:40 PM

Thanks for the suggestion. I'll have coordinate a time later with my wife to allow for another whole-house power-down and try that.

I earlier found this statement (see below) and decided that #2 was my situation. It sounds like I now have two different people saying that's not the case...I guess this is probably good news...

The most common causes of tripping for AFCIs have been found to be:
1. Ground to neutral faults through loose connections in receptacles.
2. Shared neutrals where a 3-wire home run is used with single pole AFCIs or a ganged 3-way
switch is tied to the neutral of another circuit

mhops 08-01-2009 06:21 PM

You guys are great. Your suggestions were right on the mark and I found the problem -- a ground wire in a junction box that had been placed right over a neutral screw. What a relief!! We are all systems go now.

brric 03-17-2010 06:16 AM

{Moderator note: this is a reply to a post that has been removed}

Your comments are of no help to anyone. Many of us on this site are highly qualified. If you don't want to help that is fine. We all know people are going to do this work themselves. Personally I am here to try and help them do it correctly and to help prevent them from getting incorrect instructions and information. Sorry if it offends you.

jbfan 03-17-2010 06:30 AM


Originally Posted by BK Alley (Post 415834)
post removed

And what did we say that we know just enough to be dangerous?

You joined the forum just to criticize one post, without offering anything of value.

Just another internet troll!

BlueBSH 03-17-2010 07:12 AM


Originally Posted by BK Alley (Post 415834)
post removed

If certified electricians know "just enough to be dangerous" then I am going to question every wire in the world as right or wrong :laughing:

Leah Frances 03-17-2010 07:58 AM

{Moderator note: this is a reply to a post that has been removed}

I always wonder about these - and at least we have the original post this time.

Wonder if the now-absent poster was surprised that people didn't take kindly to his advice that we 'check our egos'.

mhops 03-17-2010 11:09 AM

Wow, things got heated around here after I stopped checking!

Thanks again to those who offered helpful comments.

I have had all of my work inspected and everything has been signed off. I continued to have some trouble with my new AFCI circuits tripping, so I brought in a professional. He had no problem with my work, but said that the Siemens AFCI breakers that I used are notorious for this problem. He suggested I add a subpanel and replace all of these with Cutler-Hammers. I am having him come out tomorrow to take care of this for me.

I am very happy to have done this work myself. I learned a lot, saved a lot and have strong sense of pride and accomplishment. We love our new, finished basement.

Happy spring everyone!

brric 03-17-2010 11:22 AM

Personal preference I guess. Never had problems with the hundreds of Siemens AFCI"s we've installed.

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