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Sacslc 11-13-2010 06:02 PM

Loss of power and AFCI tripping
I have a rather unique problem with two circuits in my home. Let me start by stating that the electrical contractor who wired my home is no longer in business. About two months ago I lost power to my family room while I was home. Assuming the breaker tripped I went out to the garage to reset the breaker. When resetting the breaker didn't work I removed the pannel cover and discovered that there was no circuit wired to the breaker for the family room. Further inspection revealed that the breaker above it (AFCI) for the downstairs bedroom next to the family room had two wires connected to it, one black and one red both from the same Romex. I was able to determine that the black was for the bedroom and the red at that time didn't seem to go to anything. When connected to the family room breaker I still had no power. I made the assumption that I might have an open to that circuit somewhere. After troubleshooting for several days I decided to run extension cords to power this room until I could spend more time on it. Today I connected the red wire to the family room breaker again and energized it. Much to my surprise the circuit was now working for that room. The downside is that when I turned on the lights to the family room the AFCI tripped for the bedroom. I unpluged everything from both rooms and removed the hot wires for both of these circuits at the pannel to see if there was a short to neutral or eachother. I measured opens in every case. As long as I have no load in the family room I can energize both circuits. As soon as a load of any kind occurs in the family room the AFCI for the bedroom trips. The Bedroom has been working fine through all of this so I have not susspected anything in that circuit. What I don't understand is how the two circuits are tied together. That may be the hint to why I am having problems. To the best of my knowledge they should be completely independent. I have heard of other people complaining about AFCI's tripping from loads in surounding circuits I just have not found an answer as to why this is happening. I suppose it is possible the AFCI is bad but then why doesn't it trip when I turn on the light switch on that circuit. Also for a very long time both rooms were working off of the same breaker, the AFCI. I would appreciate any advise anyone has. I have to figure this out before the wife is ready to put up the Christmas tree or I'll be hearing about it. :)

a7ecorsair 11-13-2010 06:22 PM

In your panel box, if you follow the black and red wire back, do they come from the same cable? If so, that means they are sharing a neutral.

Sacslc 11-13-2010 06:51 PM


Originally Posted by a7ecorsair (Post 533729)
In your panel box, if you follow the black and red wire back, do they come from the same cable? If so, that means they are sharing a neutral.

Yes it is the same Romex cable so both circuits are sharing the neutral. If I power both circuits independently they work fine. It's when both circuits are energized that the AFCI trips.

kbsparky 11-13-2010 06:55 PM

It sounds like those 2 circuits were originally wired up as a Multi-Wire-Branch-Circuit (MWBC). Probably the electrician did that, not thinking he had to use an AFCI breaker until it was time for final inspection.

You can not share a neutral on a single-pole AFCI breaker. Attempting to do so will cause the breaker to trip as soon as any load is applied, as you have discovered.

About the only easy remedy for you at this point is to connect both the black and red leads together on the same AFCI breaker. If and when a 2-pole common-trip AFCI breaker becomes available, then you will be able to split those circuits back up.

A not-so-easy remedy would be to back-feed the other room with a new home-run circuit from the panel to one of the outlets. You would have to find the point where the multi-wire circuit is split up, and disconnect the neutral connection for the red wired circuit there.

a7ecorsair 11-13-2010 06:56 PM

Missed it, I see in your post that the red and black come from the same cable. I looks like they tried to wire this as a MWBC but with the AFCI it didn't work so they stuck both wires into the AFCI. Since it has worked, I'd say you have a bad connection somewhere in the circuit. You will have to open up each outlet box, receptacles and lamps, and look for a bad connection which could be a loose wire nut or even some backstabed outlets. It's hard to say what you will find.
To straighten this out and fix the wiring error will take some time. You don't have a separate neutral for the family room.

Sacslc 11-13-2010 07:08 PM

Thank you these have both been great responses. I can't believe this passed inspection when the home was built 7 years ago. That explains why I found both circuits wired to the AFCI. When the orriginal power failure occured both were wired to the same breaker and the family room lost power but the bedroom did not. It's been a couple months now and the family room circuit appears to be working. I would susspect that there is an intermitant open somewhere in the circuit. My fear is that this electrician put a staple or nail through the romex somwhere in one of my walls and it is just now begining to cause problems. I was not aware you could not share a ground with the AFCI breaker so that has saved me a lot of troubleshooting steps. I am going to wire them both to the AFCI and wait to see what happens here down the road.

Sacslc 11-13-2010 07:31 PM

Well that didn't take long. I moved the red wire back to the AFCI and energized both circuits. Everything worked for about 1 minute and then I lost power to the family room. The bedroom still has power. When I had moved the red wire to the family room breaker by itself it worked for quite a while with no problems except for the fact that it was tripping the AFCI on the bedroom circuit. I really don't know what to do now. I can't imagine I have a bad light switch or recepticle. Any suggestions?

a7ecorsair 11-13-2010 08:04 PM

I posted what to do in reply #5.
The cable in your panel that has the red black and white wire has to go to some box some where. When you find it, you will see two branches. The black wire and white wire will go one way and the red wire and white wire will go a different way. The white wires will be connected most likely with a wire nut. This is where the two circuits separate.

Sacslc 11-13-2010 08:20 PM

I had already previously followed the romex from the pannel to the attic. It runs down the wall to our upstairs bedroom. From there I can only assume it continues to the downstairs bedroom directly below. Is it likely that it is fed into a recepticle box or switch first? Is it also possible the split is in a junction box somwhere hidden behind a wall or ceiling? I haven't had any luck finding where it splits to see if power is getting at least to that point. I have pulled out every recepticle and switch. It's so strange that the circuit just opens up. Is it possible for a recepticle to become intermitant and open up? My other thought is that there is a bad wire nut connection somwhere. Thanks for the help.

Sacslc 11-13-2010 08:25 PM


Originally Posted by a7ecorsair (Post 533805)
I posted what to do in reply #5.
The cable in your panel that has the red black and white wire has to go to some box some where. When you find it, you will see two branches. The black wire and white wire will go one way and the red wire and white wire will go a different way. The white wires will be connected most likely with a wire nut. This is where the two circuits separate.

I missed part of your post too I'm afraid. I missed the point you made about backstabbed outlets. I had already found one loose connection on a light switch but it was not the problem. I'll go back and check each again. Are light fixtures worth checking since they are suplied power by the switch? I would think if it was a light fixture the circuit would work except for the fixture. Is this false assumption?

a7ecorsair 11-13-2010 08:59 PM

It is very possible that the cable ends up in a ceiling box and splits from there. Open every box that you know is on either of the circuits.

Sacslc 11-13-2010 11:48 PM

Well I have checked every box with a receptical, switch or fixture. I found no loose connections and saw no indication of a split. I don't know where the cable feeds into the circuit. I lose physical sight of it once it drops from the attic and into the wall. My guess is that it comes into the bedroom and then branches off to the family room from a box behind a wall. Is there anything I can use to try and trace this without tearing out my drywall? The part that doesn't make any sense is that it worked today after sitting for weeks and then just opened again. It seems to me a loose connection would be more random and subject to some sort of physical change in its condition. I'm a EE and have anylized a lot of problem circuits. I've just never had to troubleshoot anything hiding behind walls! This is by far one of the strangest things I've encountered. I may just have to call an electrician if I cant start making some progress.

a7ecorsair 11-14-2010 08:55 AM

Do you have smoke detectors that are AC powered and interconnected? Don't overlook those boxes. Did you check all the closets too? I would hope there isn't a hidden box, code violation, but you could have a box with a blank cover that has been painted or sprayed and not very visible.
Because it looks like the original intent was to have the bedrooms on the AFCI and the dining on the standard breaker, one would think the junction would be close to one of those rooms. How many bedrooms and how many levels is the house? Are there any other AFCI's in the panel?

Sacslc 11-14-2010 01:56 PM

We have 4 bedrooms total in the house and all are AFCI protected. The downstairs bedroom is right next to the family room and both share the same Romex cable and a neutral which explains why both rooms are wired to the AFCI. I have a breaker for the family room but it is not being used. I know of one hiden box for sure in the ceiling of our down stairs bathroom. The only reason I know this is because we took a fair amount of pictures during the construction of our home. Unfortuneately I was not intentionaly taking pictures of the electric and plumbing something I will deffinitely do if we build again. I can see some of the roughed in electric though. There is a blue junction box on one of the studs in the ceiling of the downstairs bathroom which is right next to the bedroom. Yes I have smokes wired in to the AC but they are all on the same breaker. I'll check those boxes as well. I just checked the closet and their doesn't seem to be any boxes painted over. Thanks for all of the great info. I really can't wait to find out what this is.

chayce 11-14-2010 09:12 PM

You could try a breaker finder the ones that have the little plug in dongle and beeper work very well for tracing wires and you can get em for around $25. Also you might be missing something since all junction boxes should be accessible either from the attic or from the house but it could also be a sleazy electrician. Heck it could be two wires splice without a box, I've seen worse. Either way with your problems you should be tracing out as much of your homes electrical as possible since the problem you see might be the tip of the iceberg.

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