Installing ceiling light fixtures, Six wires to deal with

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Old 08-27-09, 07:16 PM
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Installing ceiling light fixtures, Six wires to deal with

I am an electrical novice, but when installing light fixtures in my small 1924 Los Angeles home (updated to modern electrical wiring at some point), I was successful in several of the rooms. But when I came to the last room (office), there were six wires coming out of the ceiling box: 2 white, 2 black and 2 copper. When I installed a fixture, the light came on but then stayed on (the light switch doesn't turn it off) and a light in another room went out. I have since tried different random configurations all with no luck. The light in the other room continues to not work. But they do work in several other rooms.

I will add that many of the rooms had ceiling fans in them which were removed when I moved in which I think accounts for extra wires in some of the other boxes (others had 1 black, 1 white, 1 red, and 1 copper). I am installing regular light fixtures with no fans.

Any help or suggestions would be greatly appreciated.

Thank you.
 
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Old 08-27-09, 07:37 PM
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there were six wires coming out of the ceiling box: 2 white, 2 black and 2 copper
Actually 4 wires plus grounds. I'll guess two cables. Please confirm. You need to determine which cable is hot. Check for voltage between the black and white of each cable. After finding which cable is hot turn the power off and use the ohm function of your multimeter to check for continuity of the other cable. Have a helper flip the switch and see if you get continuity when the switch is on and infinity when the switch is off.

If you determine one cable is always hot and the other cable goes to the switch connect the white of the switch cable to the black of the light. Connect the black of the switch cable to the black of the hot cable. Connect the white of the light to the white of the hot.

Note the white of the switch cable should be recolored to black or any color except white or green.

As to the other light there are not enough wires in the box to explain why it doesn't work if my assumption of a hot and switch loop is correct..
 
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Old 08-27-09, 09:35 PM
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Thank you for your reply. I was hoping that I could do this without purchasing a meter but I suppose I'll have to get one. After reading your post I looked more carefully at the box and see that there are two groups of wires coming out of separate holes, each has one black, one white and the copper ground.

I'm assuming continuity and infinity are readings on a meter (sorry I'm a novice).

When you say "If you determine one cable is always hot and the other cable goes to the switch connect the white of the switch cable to the black of the light" How will I know which cable goes to the switch?

Regarding the other light, it did work before I tried to install this last fixture.

Is there a particular kind of meter I need to buy for this?

Thank you.
 
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Old 08-27-09, 10:10 PM
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If you don't have a meter there is another way. Turn off the breaker. Connect the light you are going to install to one of the cables. Turn on the breaker. If it lights you have found the hot. Turn off the breaker and disconnect. Just to be sure only one cable is hot check both cables..

You can safely guess the other cable is the switch loop. Follow my instructions in the previous post.

An cheap analog not digital multimeter is good for this kind of work. Digital meters can give false readings because they don't load the circuit enough.

General suggestion when removing an old light fixture disconnect only the two wires and ground going to the fixture. Leave all others as is.
When you say "If you determine one cable is always hot and the other cable goes to the switch connect the white of the switch cable to the black of the light" How will I know which cable goes to the switch?
It is the one that isn't hot, shows 0 volts.

 

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Old 08-28-09, 02:27 PM
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Ray,
Thank you so much for your help on this. I did just what you said and it worked! The light and switch are now working in the office.

However, I can't get anything to work it the bedroom. Out of the ceiling box are two sets of wires, 1. a black and a white and 2. a red and a black. There don't appear to be grounding wires. I tried to figure out (without a meter) which wires are hot, but none of the combinations worked. Do you have a guess as to what's going on here?

Thanks again.

Jim
 
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Old 08-28-09, 02:34 PM
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Can you tell the number and colors of wires in the switch box and connected to the switch?
 
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Old 08-28-09, 03:11 PM
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Out of the ceiling box are two sets of wires, 1. a black and a white and 2. a red and a black. There don't appear to be grounding wires.
Does it look like the wires come in through conduit (pipe) rather then cable? Red and black would make sense with conduit but not cable. This being Los Angles I was expecting to see conduit not cable so it wouldn't surprise me. This answer and the answer to PCBoss' question may confirm what I'm thinking. You say though the light doesn't work tied directly to the black and white pair?
 
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Old 08-28-09, 10:15 PM
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I opened the switch box tonight. The two wires connected to the switch are red and black.

Shining a light up into the ceiling box it appears to be conduit.

I can try something again in the morning.

Thanks again.

Jim
 
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Old 08-29-09, 07:34 AM
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Originally Posted by bimmy View Post
I opened the switch box tonight. The two wires connected to the switch are red and black.

Shining a light up into the ceiling box it appears to be conduit.
That makes since. The black and white pair of wires at the ceiling box should be the hot pair. Try again as a test to hook the light directly to them and be sure the bulb is good.
 

Last edited by pcboss; 08-31-09 at 01:23 PM. Reason: fixed quote
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Old 08-29-09, 02:07 PM
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I tried again in the bedroom with two different fixtures and different bulbs. No luck.

Is it possible that this fixture is somehow linked to the other room (office that's now working). Remember this bedroom light used to work a few months ago until I attempted to install the office fixture.

Is there something else I can try, or is it time to call an electrician?

Jim
 
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Old 08-29-09, 03:05 PM
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I don't see how it could be the office light because there are only 4 wires. However open the switch box and check how many wires are there. I would only expect to see two. Did you do any work on any receptacles? I believe you said you changed out other lights. It could be one of those.
 
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Old 08-31-09, 01:03 PM
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There are two wires, a black and a white, and a copper ground wire in the the light switch in office.

I did install ceiling light fixtures in four other rooms. All of them are working. Are you recommending that I open them up, and if so, what should I look for?

Thank you.
 
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Old 08-31-09, 06:16 PM
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Have you tested the black and white pair with the switches of all the lights you replaced on?
Are you recommending that I open them up,
There is no way to know for sure. It could even be a bad connection at a receptacle. Are there any receptacles on the same breaker as the lights? Are all the other lights on the same breaker? Did it work before you put the other lights in? I think you get the idea. At one of the fixtures on the same breaker as the non-functioning light the black and white wires are supposed to be connected but aren't.

I would probably use a volt meter or test light to further check the black and white pair. I would plug in an extension cord and with the breaker on check voltage between the narrow blade slot of the extension cord to the white then the black. Narrow blade slot to black should be either 0v or 240v. From the narrow slot to white should be 120v. Wide slot to black should be 120v. Wide slot to white should be0 volts. Of course this assumes using a polarized or grounded extension cord in a properly wired receptacle. It is also somewhat dangerous so you must be very careful.

The above tests are not absolutely necessary but might help give some insight.
 
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