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-   -   Ceiling Light Fixture Blows Up Bulb (http://www.houserepairtalk.com/f9/ceiling-light-fixture-blows-up-bulb-11153/)

CMHbob 04-15-2011 08:00 AM

Ceiling Light Fixture Blows Up Bulb
 
I just bought this house and I'm replacing a fixture in the ceiling, controlled by a wall switch. It's old and doesn't match the style of the other, newer fixtures. Plus it doesn't have a bulb so its time for it to go. I replace the fixture with a new one and screw in a new incandescent bulb.

When I flip the switch, the bulb shatters. I'm thinking its a defective bulb, so I put a new bulb in its place and flip the switch. Same thing happens. Its highly unlikely that that 2 bulbs are defective, so I install the old fixture with a working bulb from another fixture. When I flip the switch, the bulb shatters. Just to be sure, I install the new fixture in another room with a new bulb and everything works as expected. At this point, I think I have eliminated the fixture and bulb as the source of the problem.

Then I test the wires in the ceiling box with a voltage sensor. When the switch is off, the neutral (white) wire is hot (i.e. live with voltage). When the switch is on, both the neutral and line (black) wires are hot. When I turn off the circuit breaker for this room, both wires are not hot.

Any idea what is causing this? I am not afraid to work with electrical wiring, so I am hoping someone can tell me how to fix it.

kok328 04-15-2011 12:29 PM

You have identified the switch leg. The white wire should have been marked with black tape to indicate that it is actually a hot wire.
Effectively, the white wire is hot and is sending power down to the switch.
From the switch, the black wire brings the power back to the the fixture.
You should not connect the white wire to the fixture.
Connect the black wire in the ceiling box to the black wire on the fixture.
However, your still missing the neutral wire to connect to the fixture.
Any other wires in the ceiling box?

JoeD 04-15-2011 03:55 PM

You need an actual voltage tester. It sounds like you are applying 240 volts instead of 120 volts to the fixture. Is this a home or industrial setting? Industry often uses 277 volt lighting.
How many breakers does it take to kill the power to both the white and the black wires?

CMHbob 04-16-2011 09:12 AM

Answers for JoeD
 
Quote:

Originally Posted by JoeD (Post 55967)
You need an actual voltage tester. It sounds like you are applying 240 volts instead of 120 volts to the fixture. Is this a home or industrial setting? Industry often uses 277 volt lighting.
How many breakers does it take to kill the power to both the white and the black wires?

Volt meter reads 240V. It is residential setting. [This room was remodeled by a previous owner and made into a laundry room with a new door into the kitchen. The original door (now closed off) opened into the garage and the room was used as a shed. I have seen other homes in the neighborhood with the original design.] One breaker kills the power to both wires.

CMHbob 04-16-2011 09:21 AM

Answers for kok328
 
Quote:

Originally Posted by kok328 (Post 55961)
However, your still missing the neutral wire to connect to the fixture. Any other wires in the ceiling box?

The only wires in the ceiling box are the 14/2 coming from the switch and another 14/2 leaving the box. The wire leaving the box is much older, wrapped in black insulation. My guess is that the black-insulated wire was part of the original building (circa 1960s) and the switch was added later.

kok328 04-16-2011 01:28 PM

Assuming the old fixture worked from the switch prior to you changing it out. It would be a simple matter of putting the wires back the way they came off the old fixture onto the new fixture.
I still suspect that the white hot leads to the light switch and the black returns from the switch to the fixture.
Take a look at the light switch and verify this.

JoeD 04-16-2011 09:12 PM

Quote:

Originally Posted by CMHbob (Post 56012)
Volt meter reads 240V. It is residential setting. .......... One breaker kills the power to both wires.

One breakers turns off 240 volt power in a residence?? There is something very very wrong here.
Is this a subpanel? I am thinking the only way this can be is if the neutral and one hot are somehow swapped in the panel feed and there is no ground bond.

kok328 04-17-2011 06:37 AM

A single two pole breaker will provide 240Volts.

CMHbob 04-17-2011 09:00 AM

Uh Oh!
 
After an hour of trying to figure this out with no success, including the suggestions made in earlier posts, the frustration was just too much. I started taking the ceiling & wall drywall down to trace the wires back to the switch and to the panel. BTW, the circuit breaker was being thrown when I flipped the switch and I forgot to mention that fact.

I found an old hidden connection box in the ceiling that was the source of the older, black wire in my ceiling box. There were two hot wires feeding the light fixture which was just too much for the bulb when I flipped the switch. I rewired the room properly and the switch now works the light fixture without blowing the bulb.

Fortunately the panel is located in this room, so there was not too much damage. I don't think this ceiling light ever worked and the previous owner never fixed the problem, leaving it for the next guy to repair. Now all I have to do is to patch the drywall, paint the walls and ceiling. At least I have plenty of light to finish the job.

JoeD 04-17-2011 03:39 PM

Quote:

Originally Posted by kok328 (Post 56032)
A single two pole breaker will provide 240Volts.

Please explain how in a residential 120/240 panel.


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