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I just replaced a broken light fixture in my closet. (The switch in the light fixture broke when I pulled too hard on the chain.)

When replacing the light fixture I noticed that there is only 30 V AC between the white and black wires. The ground wire is cut back and is not being used. By the way, the wiring in my house is all aluminum.

I know the new light fixture works. I checked it out with my multimeter, and I tried it in a different closet. But the light bulb won't turn on because there is only 30 V. (Even if I disconnect the light fixture completely there is still only 30 V.

It seems to me that it must be a problem with the wiring. My attic does provide some (difficult) access to the wiring, but I am not sure where to start looking for the problem or what to look for. Can anyone offer some suggestions?

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The first thing I would do is take your multimeter and go to another fixture and make sure you see 120VAC on it - just to make sure the meter works correctly (assuming you are in a 120VAC country) –  Aaron Jan 18 '13 at 20:41
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Sounds like you have a bad connection somewhere. This can easily happen with aluminum wiring and is a fire hazard. –  BMitch Jan 18 '13 at 22:43
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2 Answers 2

Are you sure the circuit was live when you measured it? If you try to measure an open (i.e. off) circuit, you can sometimes read a "phantom voltage" caused by coupling with other nearby live wires. Phantom voltages can't generate a significant amount of current and are therefore harmless, but they can be measured by a multimeter.

If you say the fixture doesn't work even though the old one did, perhaps a connection came loose somewhere and now you have an open circuit with only the phantom voltage. Or maybe you just forgot to switch the breaker back on?

I don't see how the old fixture could've worked if it was actually only getting 30 volts, so something must've changed during your installation.

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This can happen if you use a 3-way switch. Lower voltage will cross the travelers.

A "live" circuit will carry the 110, an "off" circuit may carry some lower voltage.

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This light isn't on a three way switch. but I will definitely keep this in the back of my mind. –  Stainsor Jan 20 '13 at 20:42
    
30V should, then, be very unlikely in a direct circuit... even with poor connections. Try checking potential from the neutral to ground and see what you get. –  Matthew Jan 22 '13 at 17:29
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