Hi all, tonight my wife flipped on the attic lights and the circuit breaker tripped. This is a 15amp circuit, covers a bathroom as well, so there is a GFCI breaker on the circuit. Running at the time on the same circuit were a printer (stand-by mode), a wireless router, a PoE ethernet switch, and a 18" flourescent overhead light. The attic lights are 5 60W bulbs on a single switch. About 10 seconds after turning them on, the breaker trips. I thought the breaker might be bad, because this hasn't happened ever before, and switched the breaker with another identical one - which resulted in the same behavior. I checked the bulbs, they are all tight. What else should I look at before calling in the professionals?

Typically I don't advise people continue to energize and load a circuit that is tripping.

But stand by the printer and have your wife flip the attic lights again.

It might be enough of a draw that the printer cycles, and if it is laser printer, the fuser pulls a pretty a decent load when energized.

Is there a UPS/battery backup on that circuit?

Does the GFI self test OK?

Mouse, squirrel, loose connection, defective part?
An easy check would be to disconnect every thing and remove the bulbs then check if power stays on, if so shut off reinsert one bulb, etc.

Looked up and calculated the power draws for the appliances, should be well under the circuit's 15Amp load.

PoE Switch - 2Amp Max
Router - 1.58Amp Max
Bulbs - 2.7Amp (300W @ 110V)
Printer - 0.10 Amp Sleep, 6.5Amp printing
Flourescent Light - 0.36Amp

6.74Amp, 13.14 Amp printing (which it was not).

Anything to enlighten me?

Thanks for the replies. In my edit above, if I cut everything else off, the lights run find, leading me to believe it's something else. I did turn the printer off completely, leaving everything else on, and it still tripped.

Looking at wires in the attic, all looks well, I do not see any evidence of a squirrel/rodent.

There is no UPS system on this circuit. Their is a surge suppressor that the printer, switch, and router are plugged into.

The GFCI breaker does test ok (both of them, I switched them out, the same thing happened).

It doesn't take much to trip a GFCI. Any problem in any of the lights, switches, wiring will trip it.

Time to start isolating things and turning them on or plugging them in one at a time.

Do you have an attic fan?

No attic fan. One other room's lights/plugs on this circuit, but nothing turned on there.

I'm not an electrician but I do work as an electronic tech. It sounds like a possible short. Bad appliance/socket/outlet. I would test it by tripping the breaker off, unplug ALL devices (unscrew bulbs AND florescent fixture. Use a VOM to see if there is continuity still on the circuit. That means a short. If not, then the issue is in one of the devices/fixtures.

My two cents to help diagnose more safely.

How old is the GFCI?
I've been told they can weaken with age.

The GFCI outlet could have failed.

I would look to get the computer equipment off that circuit and put it on a circuit with surge protection and battery back up as needed.

My wife has to much draw in the bathroom circuits, hair dryer curling iron etc to put computer equipment on it.

Everybody please just read the thread before posting.

quote:

The GFCI breaker does test ok (both of them, I switched them out, the same thing happened).

A 15 amp breaker has to trigger at 15 amps or less. Having said that, how old is the flourescent lamp ballast?

Its the lights/fixtures I bet.

The surge protector may be getting flaky. If not that, then take the easy path and change out the attic bulbs for LEDs. Lower the total load.

It sounds to me that it is not a load issue, but a ground fault issue and that is what is tripping. I would check all of the wiring connections and sockets in the attic.

Thanks for all the suggestions. As I said, the breaker is good, and in fact, I switched it out for an identical breaker and the same thing happened. Nothing has changed within the circuit or what is on it for at least 6 months. Tomorrow, I will go through the attic wiring, and isolate the individual loads to see if I can find something more specific.

I think Jim Theo gave you some excellent advice above. Quick & dirty way to determine what to chase...circuit problem or device problem?
A clamp-on ammeter could be very handy, also...watch it as you start adding devices back on if your troubleshooting takes you in that direction.

If it only happens when the attic light is switched on then you have a fault in one of the boxes, or the wiring between fixtures. Likely either animal chewed threw wires or when they were originally stripped they knicked the wires with razor knife.

I'd start in the middle of the lights, remove the keyless fixture and disconnect the wiring. Then try to switch it on. If it holds, check wiring at the end of disconnected lights. If it trips look at switch and wiring to first two lights.

I'd try replacing the GFI Outlet. I had a issue anytime my garage door would open or close. The breaker would trip. Found out there was a GFI outlet in the circuit on the wall.

Replaced the outlet and all is well.

quote:

Originally posted by myrottiety:
I'd try replacing the GFI Outlet. I had a issue anytime my garage door would open or close. The breaker would trip. Found out there was a GFI outlet in the circuit on the wall.

Replaced the outlet and all is well.

This guy is a man of action who throws cation to the wind. Not only did he reply before reading the thread, he didn't even bother to finish reading OP before posting.