Replacing an old light fixture.
June 6, 2005 12:15 PM   Subscribe

I would like to replace an old wall sconce in my bathroom. Is this something that I, being a very un-handy person, could/should try to do myself? Or should I just hire an electrician?

The shiny new replacement I picked up has a black wire, a white wire, and a green ground wire. There are two scary looking brown frayed wires coming out of the wall (connected to the old sconce), and no obvious place to attach the ground. So my questions are: 1) does it matter which wires I connect to the black and white wires on the new sconce, and if it does, how can I tell which connects to which? 2) Does it matter if I don't connect the ground wire? 3) given that I'll turn off the power at the main circuit breaker before attempting this, is there still a risk of getting shocked or starting a fire when I turn the power back on after making the replacement? The new sconce also has a power outlet that I'd like to use, if that makes any difference.
posted by nixxon to Home & Garden (8 answers total)
Best answer: 1) Yes -- One is going to be "hot" when the switch is flipped, and the other is going to return that voltage to the "neutral bus bar" in your fuse panel (I assume fuse panel given the state of your wiring).

1b) You're not going to like it: Either call an electrician, or do this test: Get an AC induction tester (looks like a little pen, and it lights up when it's near high voltage). Turn off the power to the room and test with the induction tester to be sure it's really off. Remove the old fixture and place "wire caps" (sometimes called "wire nuts") on the end of the two exposed wires. Turn the power back on and flip the wall switch. Touch the induction tester to the insulated wires; whichever one makes the tester beep is the "hot" wire, and should be connected to the black wire in the new fixture.

2) With incandescent lights, technically, no; your local electrical code may disagree, however. Your fixture, however, has a grounding plug on it, which means: YES, it MUST be grounded. If your wires are in conduit (doubtful, but hey, I may as well point out the option), you can simply tie the wire to the wall box for the light fixture with a common "green grounding" screw (they're standard sizes, just pick up a box at your local home improvement store).

3) Circuit breaker and old non-color-coded wires? Wow. After you make the replacement, and you're certain that you've wire the fixture to the correct wires and applied the wire nuts correctly (and, since you're new at this, wrapped them twice with electrical tape) there is imperceptibly little risk of causing a fire or getting shocked by turning it on. Again, because the new fixture has an outlet, IT MUST BE GROUNDED. Don't let anyone tell you otherwise. It's the law. In fact, since it's in your bathroom, it must be a "GFI" outlet, or placed in-line with a GFI outlet, which means you should probably find a new fixture, or wire the outlet portion of the fixture separately.
posted by Merdryn at 12:46 PM on June 6, 2005

I encounter this problem frequently in my house and I'd like to hear some expert advice. One problem you face sometimes is more than one circuit running through a fixture box. So, if you're uncertain whether you've cut off the juice, get yourself one of these. It's a non-contact voltage detector that basically tells you if you're still live.
posted by sixpack at 12:50 PM on June 6, 2005

Merdryn: Assuming no conduit (and in a non-wet/non-GFI outlet) what is one's option for grounding? Is there ANY option other than rewiring the circuit?
posted by sixpack at 12:58 PM on June 6, 2005

There are two scary looking brown frayed wires coming out of the wall

This sounds like a job for electrician-man. Frayed supply wires is not something a tyro should be working on.
posted by Kirth Gerson at 1:16 PM on June 6, 2005

If the insulation on the wires is frayed, then that suggests that it's the old, old bitumen-and-fabric-wrap insulation. My house has some of that, and the wiring was put in around 75 years ago. It's fine if you don't touch it, but as soon as you bend a wire, the insulation breaks and comes off. Bad, bad mojo.

nixxon -- call an electrician. Unless you know what you're doing here, you run a very real risk of electrocuting yourself or someone else, or causing an electrical fire.

Really. It's not worth it.
posted by 5MeoCMP at 1:21 PM on June 6, 2005

Best answer: If the insulation is falling off of your wires I would call an electrician. This sort of stuff is pretty cheap and you are putting your house at risk if their is a short due to insulation failure, not to mention your health.

If the insulation is OK and you do decide to wire it yourself then the outlet in the fixture must be addressed. If it is not a GFI outlet then you must wire it into a GFI protected wiring. This can be a GFI outlet upstream. If this seems too much, and you are going to wire it yourself, then remove the wiring between the bulb and the outlet so that the outlet remains unpowered.

Also, if your outlet or outlets in the bathroom are not GFI they should be replaced with GFI outlets. If you have multiple outlets wired together only the upstream outlet needs to be GFI; it will protect the downstream ones. This is a trivial job; just follow the instructions that come with the outlet and Merdryn's excellent instructions for determining which wire is hot and which one is neutral. When you are done, test all of the outlets with a simple GFI tester. This is a plug with some lights and a test button. It costs only a few dollars and will verify that everything is wired correctly and it lets you test the downstream outlets.
posted by caddis at 1:40 PM on June 6, 2005

If the wiring has no ground you can legally use a GFI as a ground defeater (I know this for CERTAIN in Canada, it is likely also in the NEC). This is, of course, because a short to ground on a GFI of even a miniscule scale (3 or 4 mA) will trip the GFI, and is actually safer than relying on the ground wire to trip your 15 A breaker.
posted by shepd at 2:08 PM on June 6, 2005

Response by poster: Thanks for the replies, everyone. This project is clearly way out of my league!
posted by nixxon at 4:27 PM on June 6, 2005

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