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MikeCT
Old Wiring, New Lamp

Hi,

I'm new to the site and thought I'd ask a question. I have a 1939 home in CT. I'm installing a new outdoor lamp over the garage and I can't tell which wire is "white" or "black". I guesses and popped a breaker. I'm wondering if I do the opposite would that mean I have it right or does this mean there may be other trouble?

Appreciate the help. Electrical has never been my strong point.

Mike

dj1
Re: Old Wiring, New Lamp

Reverse the wires carefully, should be OK.

Condoman
Re: Old Wiring, New Lamp

I was working on my Dad's house and had the same problem. I made up a long single conductor wire that I could ground and then use that with a voltmeter to test between the two wires. The live wire was then wrapped with colored tape. You may measure some voltage between the ground and the neutral wire and that may be normal.

dj1
Re: Old Wiring, New Lamp

To avoid such mistakes, such as which wire is the hot and which one is white in the future, mark the wires BEFORE you disconnect them.

When I work on replacing circuit boards, where I have a dozen wires or more, it's critical to label all wires as you disconnect them.

Fencepost
Re: Old Wiring, New Lamp

Based on the age of your home and the description of the wires, you likely have old wiring that's insulated with rubber and covered with a cotton overbraid. Over time, this overbraid has discolored with age to the point you can't tell the difference between the wires. If you look carefully, you may see that the cotton overbraid on one wire has a black thread woven through it. This is usually the hot, but not necessarily so: testing as described by condoman is the best way to be sure.

Chances are the rubber insulation on the wire is brittle. I recommend putting heat shrink tubing over these wires before installing the fixture. Use a heat gun -- not a match or torch -- to safely shrink the tubing.

JLMCDANIEL
Re: Old Wiring, New Lamp

Some detail must be missing in the post, even if you reversed the wires on a new lamp it should not trip the breaker.

Jack

MikeCT
Re: Old Wiring, New Lamp

I have not tried swapping the wires yet but I think everyone understands the problem. Fencepost hit it dead on. This was an outside light and the wire coverings were completely disintegrated. I wrapped both wires in electrical tape before I attached the lamp.

My main question is what Jack mentioned. I would not think that reversing the wiring would cause a breaker to trip. There may be more to this but I'm sure. I will try reversing the wires in the next few days. If I have the same result I'll get an electrician.

I really appreciate the responses. Thanks!

Fencepost
Re: Old Wiring, New Lamp

It's quite possible that what's causing the breaker to trip is the disintegrating insulation. Even though you taped them up, where the wires enter the box it's extremely difficult to put tape. There may be bare spots allowing the wires to touch each other or ground out to the box.

I recently fought a similar problem in my house, and the blame is entirely mine. When I installed a junction box for a doorbell transformer and light in my pantry, I wasn't careful stripping the jacket from the Romex and nicked the insulation on the wires. The "hot" wire was short-circuiting to the ground wire. Strangely, it didn't start giving problems until 6 months after installation. It's been hot lately and we don't have AC, so maybe the rise in temp cause the wire to move just enough to make contact.

MikeCT
Re: Old Wiring, New Lamp

I finally had time to fix the lamp. The one of the wires going into the romex was worn through and shorting out. So I pulled some of the covering back and found the true wire colors. I then shrink wrapped both wires overlapping the existing covering. At that point there were no more blowing fuses. I hung the lamp and had it on all day with no issue.

This turned out to be a simple fix and I want thank all who gave advice. I now feel confident to at least deal with hanging lamps.

Thanks again,

Mike

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