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Thread: Need help diagnosing lighting circuit

  1. #1
    Engineer chassis's Avatar
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    Default Need help diagnosing lighting circuit

    Hello,

    I am trying to install a new dining room chandelier. The old one was working fine, until it died. I can't say exactly what the cause was for the old fixture to fail.

    I have installed the new fixture and can't get it to work. There are two switches feeding the fixture, one is a dimmer and one is a toggle. The fixture has two brown wires, and one copper wire. I attached the copper wire to the green screw on the ferrule crossbar. One brown wire is connected to black in the ceiling box, the other brown wire is attached to white in the ceiling box. In the ceiling box are two red wires connected to each other. I have not done anything with the red wires.

    I have verified 120V to the white and black wires, and the fixture does not light. When the switch to the fixture is turned off, there is still 60-62 Volts across the black and white wires. Is this normal?

    I have verified continuity between one brown wire and the bulb holder female base, and continuity between the other brown wire and the male tang at the bottom of the bulb holder.

    There are no breakers out of position at the panel. I reset the relevant breaker back and forth, just to be sure.

    What are my next steps to diagnose this? Can one of the switches be bad, even if I am reading 120V at the black and white wires? Thanks for any input.

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    If a connection is not good anywhere in the circuit, your voltmeter may show 120V with no load on it, but the circuit will not support a load such as a lamp. The voltage should be checked with the load applied.

    A quick way to check your lamp is to plug it into a known good receptacle.

  3. #3
    Engineer chassis's Avatar
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    Thanks. I think this is the problem. I am going to replace the dimmer switch tomorrow and see what happens. It is a 30-is year old Lutron, and probably has given up the ghost.

  4. #4
    Test, Don't Guess! cacher_chick's Avatar
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    You don't need to replace the switch to see if it is causing the problem. You could measure the voltage drop across the switch. Alternatively, removing the switch from the circuit and connecting the 2 wires together directly would be the same as turning the switch "on".

    If you want to replace some parts, that is up to you, but I would prefer to prove them faulty first.

  5. #5
    Plumber jimbo's Avatar
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    We forgot to ask.....you have a new light fixture>>> is it either fluorescent or LED??? IF SO....get that old dimmer out of their. It will not work and may damage your bulbs. IF your bulbs are rated as dimmable ( which many are not) a compatible dimmer will run you about $120.

  6. #6
    Engineer chassis's Avatar
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    Thanks for all the input folks. It was the dimmer. I installed a new 3-way Lutron and the fixture works. I left the other 3-way toggle, and will replace it if/when it needs to be replaced.

    p.s. The fixture is not LED. I have 6 x 60W incandescent bulbs installed, because I had them on hand. When they burn out I will probably switch to dimmable CFL's, which the dimmer packaging said it is compatible with.

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