Ceiling lights turn on by themselves

Old 07-23-14, 04:17 PM
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Ceiling lights turn on by themselves

There is an incandescent ceiling light on the upper floor on my house (built in 1992). It's not a can light. The attic is above this light fixture. The fixture is controlled by 2 3-way switches, one on each end of the hall. There is no dimmer connected to this circuit. 99% of the time, the fixture works perfectly.

However, on some afternoons, always on hot days, the lights in the fixture turn on, although no switch has been turned on. When this happens, they appear slightly dimmer that normal. If either wall switch is turned to the "ON" position, the lights in the fixture turn on to full brightness, and if the switch is turned to "OFF", the lights are slightly dimmed.

After a few hours, the lights turn off, and everything works normally.

Since this never happens at night, and always during hot afternoons, I keep thinking it has something to do with the heat in the attic. But that doesn't make sense, since I've had other light fixtures that overheat, and when that happens, the light turns off, not on.

A professional electrician replaced both of the wall switches, but the strange behavior still occurs on hot afternoons. The electrician, and others in local hardware stores are stumped.

Have you ever heard of this happening? Any ideas that you have on what is causing this are greatly appreciated!

Thank you.
Old 07-23-14, 05:05 PM
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Welcome to the forums.

What I'm thinking is a nail thru the three wire between switches and just touching the travelers.

In order to come up with a solid answer we would need to know the circuit layout.
We would need to know which box the power came in.
Which box the lights were connected out of.

If you have a three way switching system set up as a switch loop to the light... then it could be anywhere in the loop.

A professional electrician should be able to remove both switches and determine how the circuit is wired.
Old 07-23-14, 05:06 PM
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I'm wondering if wires got nicked or some other part is on the very fine edge of shorting, sending power to the fixture. Hot temperatures might make things expand enough to barely complete the circuit. The way power (hot) crosses in a three way circuit means it could be anywhere; switches, fixture and wires. I'd focus my efforts on the fixture since it's accessible from below but I have seen wires damaged where a hammer missed when installing wire staples during construction. I'd probably start by tapping on the light fixture to see if you can make the light come on. Then if you can find a brave volunteer to go up in the attic on a hot afternoon and gently poke at the fixture and wire from above trying to make it flicker or turn on.

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