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amateur1 04-09-2012 06:56 AM

Electrical Short in New Light Fixture
I have just rewired a bathroom (replaced old aluminum). In the process I also replaced the light fixture over the vanity. Everything seemed OK at first and was workig fine for about a day. At some point, my wife though she heard some buzzing in the wall and the the breaker blew (it's a AFCI breaker). I tried to reset it, but it immediately tripped again. I did some troubleshooting and found it seemed to be tied back to the light fixture. I had installed a new metal box on the wall (there was nothing there before - just the wires stapled to the stud) and fed the wires through a connector, which all still looks good.

If I undid the fixture and let the wires hang down, the breaker would reset and I could turn the light switch on and off and get power to the fixture (tested with a voltage tester). However, if I re-attahced the fixture to the box, it shorted out again when I turn the switch on.

The fixture has two pieces - a mounting bracket and a cover. The cover has a green wire mounted to it and the bracket has a green screw on it. What I did to ground it was nut the green wire from the fixture to the bare wire coming into the box with a greenie and then tak the extra wire and nut it to the green screw on the mounting bracket, So in essence it's grounded to the fixture in two places, and that seems to be fine... until it touches the box. Any idea why it would start to short out once the bracket is attached to the box? And why was it fine for a day?

Any help would be most appreciated. I've installed ceiling lights before and this has not been a problem, although I'm not sure I've ever done it when I had an AFCI breaker on the circuit before.

a_lost_shadow 04-09-2012 07:38 AM

A basic question since this sounds like your first time using AFCI, did you land the neutral on the breaker or on the neutral bar? If the latter, then that's probably your problem.

Assuming the panel has been wired correctly, did you try connecting a different light, or maybe even an outlet, at the location in question. That'll let you determine if the problem is a in the light or the wiring.

gregzoll 04-09-2012 07:42 AM

If the breaker is tripping when you reinstall the fixture in the box, that means that the wires are touching ground or each other. Can you take a picture with the fixture out of the box, of the connections, and the inside of the box that it goes into please.

jbfan 04-09-2012 08:12 AM

I hope you used a gfci breaker for the bathroom.

amateur1 04-09-2012 08:48 AM

2 Attachment(s)
Thanks for the quick respnses everyone....
a_lost_shadow - I think I got the breaker on right (black and white wires to the breaker and curly white to the bus). There are other outlets\lights on this circuit that aren't having issues, so I assume they would all be affected if the breaker was the issue?

gregzoll - Picture of the box (wires.jpg).
One thing I wasn't sure of is if I needed to put a ground into the bo itself... as you can see I did not - only to the fixture (wires2.jpg).

jbfan - The outlet in the bathroom is a GFI receptacle on a separate circuit.

HouseHelper 04-09-2012 08:55 AM

Check the clamp entering the box. It may be too tight and cutting into the wires. As soon as the grounded fixture touches the box, the breaker will trip if either the black or white wire has been compromised.
Yes, you should connect the ground the box.

amateur1 04-09-2012 09:04 AM

HouseHelper - OK. So if I loosen the clamp and the sheathing is intact is that OK or could it be pinched inside the sheathing? Would I need to re run a new wire or just loosening the clamp will do it (I think I know what you're going to say...) - To ground the boxcna I simply screw in a wire to the box and pigtail it into the greenie I already have?

Jim Port 04-09-2012 09:08 AM

The wires could be pinched inside the sheath at the connector.

amateur1 04-09-2012 09:14 AM

Jim Port - OK. In which case I need to run a new wire, correct?

gregzoll 04-09-2012 10:08 AM


Originally Posted by amateur1
Jim Port - OK. In which case I need to run a new wire, correct?

Only if you can not pull any slack into the box.

amateur1 04-09-2012 10:20 AM

gregzoll - So if I have some slack, would i strip off the sheathing and tape up any pinched wires?

zappa 04-09-2012 10:44 AM

Since your wife heard a buzzing sound I wonder if it could be a loose connection on a lamp socket itself or possibly a lamp not screwed in tight enough?

kevinp22 04-09-2012 04:26 PM

more ideas
I would tend to agree with the comment regarding the loose bulb, and once it popped it may have left residue in the socket which is hampering the connection.

I have installed many AFCI in my house and they are extremely sensitive to loose connections.

1. I would clean the socked with a q-tip and rubbing alcohol (power off of course)
2. check connections
3. Also consider temporarily swapping AFCI for regular breaker

k_buz 04-09-2012 04:35 PM

It looks as if you used a razor knife to strip that romex. I would inspect those wires for any knicks in the wire especially where you ran the knife around to cut the excess off.

amateur1 04-10-2012 07:45 PM

Just a quick update. I pulled the wire out and where the wires went through the connector, I could see the hot was pinched a little and some of the wire was showing through the covering. I'm pretty sure that's what the problem was. I ran a new wire and ran it through the connector (screwing it in a little less tightly). I wired everything back up and grounded the box. Everything came back on and has been good as far as I can tell for a couple of days.

Thanks for your help everyone. If anyone thinks I'm missing something, please let me know.

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