Help a noob wire a ceiling light in an old apartment
March 10, 2013 12:31 PM   Subscribe

Installing my cheap Ikea ceiling light is proving more difficult than anticipated. The issue: after removing the old light, I can't tell which wire is which.

Totally get the hot, neutral, ground thing -- just can't tell which is which.

I have shut the power of at the circuit box, so I will probably not kill myself. I have a non-contact voltage tester.

Here's what I know:

-- All three wires attached to the old light are covered in this cloth insulation which is disintegrating.

-- One of them is vaguely reddish, the other two might have once been black or white, it's impossible to tell.

-- The two indistinguishable ones were twisted together, and attached to one wire of the old fixture.

-- The vaguely reddish one was attached to the other wire.

-- Turning on the power and checking with my tester, the reddish one and one of the indistinguishable ones is carrying current, the other indistinguishable one is not.

Based on this, can I figure out what to connect to what?

Question 2: what will happen if I connect things wrong? (Will it just not work, or will I blow a fuse, or will something explode?)

Other possibly relevant information:
-- The switch has a dimmer
-- It hasn't been working for years. When I got my voltage tester, I found out that it wasn't a current problem, so I figured this was do-able.
-- Obviously, I've never done anything like this before and don't understand electricity at all.
posted by neroli to Home & Garden (15 answers total) 9 users marked this as a favorite
ehow has some pretty good videos on how to do stuff like this. Here's one:

And youtube has a bunch if that isn't what you're looking for. I'm sorry I can't give specific advice about the old wires you seem to have.
posted by shortyJBot at 12:36 PM on March 10, 2013

Response by poster: Thanks -- yeah, I looked at a bunch of videos before attempting. Haven't yet found anything that will resolve my wire-identification problems though.
posted by neroli at 12:41 PM on March 10, 2013

Do you have a 3-way switch situation going on? That's what it sounds like to me.

The other thing I'd want to check before hooking back up is if there's 0v or 220v between the two hot legs (the reddish and the hot indistinguishable one).
posted by straw at 12:42 PM on March 10, 2013

Response by poster: Do you have a 3-way switch situation going on?

No idea. Can you talk to me like I'm really dumb? (Because I am.) There's a dimmer, like I said. Beyond that, I'm lost. And my tester can only do Yes There Is Voltage and No There Is No Voltage.

Just trying to see if based on the info above, it's possible to guess which connector takes the white wire, which takes the black, and which is the ground.
posted by neroli at 12:51 PM on March 10, 2013

Can you take a picture for us?

If you have a noncontact tester ("sniffer") you can turn the power back on and hold it to individual wires (separate from the others) to find the live ones. Be fucking careful obviously :)
posted by ish__ at 12:54 PM on March 10, 2013

It sounds like you may have more than one fixture or outlet that is connected to the same switch. Is this the case? Or do you have a 3-way switch (i.e. two switches control one fixture)?

Can you clarify how you are measuring current? It sounds like these wires are not connected to anything, which means they will not have any current travelling through them.
posted by ssg at 12:54 PM on March 10, 2013

Are there any other lights or outlets on that breaker? My guess is that the two that were connected together are the neutral/return, and when you turn on the power with the wires separated, you're seeing the return current[*] from some other outlet or fixture.

If you're certain about which wires were twisted together before, re-attach them to each other and use the voltage tester on the single wire and the pair.

(Red wires have been and still are used for the hot leg in some cases, so it's reasonable that the single, reddish wire is the hot. But definitely double-check any color coding guesses.)

[*] Not actually any current, but voltage indicating that some current would flow if you let it
posted by hattifattener at 12:56 PM on March 10, 2013

Response by poster: Don't know if this helps, but this is what I'm dealing with.
posted by neroli at 1:08 PM on March 10, 2013

Response by poster: In the above, middle and right-hand wires have voltage, per my tester; left-hand one does not.
posted by neroli at 1:11 PM on March 10, 2013

Response by poster: There are several other outlets on the breaker -- it covers kitchen, bedroom, and bathroom -- but there is only one switch for this fixture (dimmer in hallway).
posted by neroli at 1:14 PM on March 10, 2013

Response by poster: Wondering if the maybe black-coated wire currently covered by a screw connector should be unscrewed and connected to the new fixture...
posted by neroli at 1:21 PM on March 10, 2013

Best answer: You shouldn't need any more or different connections from the old fixture vs the new one.

And, yeah, I'm going with hattifattener's theory.

As long as you don't connect any wires that weren't connected before, you should be fine. The two indistinguishable ones were twisted together, which means you've got two connections to make to the lamp.

And it's a light, so neutral vs hot really doesn't matter, but I think you have it figured out here:

The red is the hot from the dimmer. Connect that to the black wire in your lamp fixture.

The other two are the chained return from another light socket, and can be treated as the neutral. Connect that to the white wire in your lamp fixture.

They hadn't yet discovered grounds back then, so if you've got a green or bare wire coming from the fixture and can screw it to the box, do so, otherwise let it dangle.
posted by straw at 1:26 PM on March 10, 2013

Best answer: Oho. Yes, the picture makes sense. Red is sometimes used for the switched hot leg. So, what you have there is a circuit coming in (white + black) from the breakers, the same circuit continuing on (white + black) to other outlets on the same breaker, and one black leg (always-on hot) diverting off to the dimmer switch and coming back as red (switched/dimmed hot). The dimmer switch, unlike a plain switch, needs a neutral as well for reference, so that's why there's also a white wire heading down the conduit to the dimmer. So, for the purposes of the light fixture, treat the red wire as the hot wire.

Here's an image I googled up of a similar situation. In your case, you don't have any of the green (ground) wires because your wiring is old, and the leg going off to the switch is black and red (more correct) instead of white and black (which is what you're allowed to make do with if you're using Romex and can't get cable containing a black and a red wire).
posted by hattifattener at 1:38 PM on March 10, 2013

Response by poster: Holy crap, it worked! Thank you!
posted by neroli at 1:41 PM on March 10, 2013

And it's a light, so neutral vs hot really doesn't matter, but I think you have it figured out here:

Yes, it works either way, but if this is a regular screw socket, then it does matter as the screw part should not be hot - the tip should be hot. This is a safety feature.
posted by ssg at 2:04 PM on March 10, 2013 [5 favorites]

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