07:44AM | 02/27/07
Member Since: 02/26/07
1 lifetime posts
I recently replaced a 2'x2' suspended ceiling panel in the basement laundry / half bath with a light fixture from Lowe's. I wired it to the same wires that go to the existing medicine cabinet / lamp over the sink, which is operated by a wall switch. The same breaker circuit also runs the lights in the upstairs bathroom, directly over this laundry room.

When I first turned on the switch with the new fixture installed, the circuit breaker tripped. I pulled one of the two u-shaped tubes out of the fixture. Still tripped the breaker. I removed the four 25-watt bulbs incandescent bulbs from the medicine cabinet light, then the new light worked. I installed two low-wattage flourescent bulbs in the medicine cabinet, the breaker tripped. With one bulb in the medicine cabinet and one in the ceiling fixture, it works sometimes but sometimes, after 10-20 seconds, the breaker trips. Funny thing is, the upstairs bathroom lights which are on the same circuit, draw much more than this new ceiling fixture, yet they never tripped the breaker, even with everything turned on.

The circuit breaker has a test/reset button on it; I think this is a GFI device. Does this, or the new fixture, have something wrong with it? I believe the circuit should be sufficient to run all these lights at full strength.

Thanks for any advice!

Jim in NH


05:12PM | 02/27/07
Member Since: 01/09/07
198 lifetime posts
The breaker is almost certainly NOT tripping because of overload; this collection of lights probably doesn't use even 20% of the capacity of that circuit.

It's tripping because of a short, or a ground-fault leakage short.

Quick way to locate this: unscrew all the light bulbs except one, and turn the power on. If it doesn't trip, turn it off again, screw in another bulb, and power it up again. Keep doing this until you find the bulb/tube that causes the breaker to trip. The problem is in the wiring to that bulb or tube socket. Most likely loose wire, deteriorated insulation, etc. (You've done some of this already -- since removing all 4 bulbs from the old medicine cabinet fixture cures the problem, it's likely one of those sockets is where the problem is. Hint: sometimes, it's faster to just pull out ALL the wiring from an old fixture & replace it with new wiring, than to try to find exactly where the bad part is.)

Generally, this will find the problem, since without a bulb screwed in to complete the circuit, it isn't a problem.

But if this doesn't seem to find the problem, it may be a loose/damaged wire near a bulb socket, which touches another wire or part of the metal fixture and short out. That could happen even without a bulb in the socket. Just the wiggling when you screw & unscrew bulbs might move wires enough to do this, and it will appear random & unexplainable.

It that seems to happen, unscrew ALL the bulbs, turn the power on, and tap with a screwdriver handle around the fixture, near each bulb socket, etc. until the breaker trips. Now you know the general vicinity where the bad wire or loose connection is located, so investigate & find it.

The third possibility is that all the wiring is good, you just have enough ground-fault leakage to trip a GFI breaker. That probably means you don't have a good earth ground. But this is more complicated to figure out, and probably something to call a qualified electrician to fix.
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