GFCI trips when I turn on one light, but not the other

[Timur Tabi]

I have a GFCI outlet installed in one room, and it shares the circuit with two other outlets and two closet lights. Both closet lights have the same kind of fixture and use the same kind of CF bulbs.

When I switch on one of the closet lights, the GFCI trips and power is cut to all outlets and lights on that circuit. However, if I switch on the other light, the GFCI does nothing and the light turns on.

I've examined the wiring for each closet switch, and they both look identical. I'm not an electrician, however, so I'm not really familiar with how the wiring works. I see green wires (ground), white wires, and black wires. The black wires are connected to the light switches, and the white wires are connected to each other. Each light switch has three of each color. I presume one set comes from the previous outlet/switch, another set goes to the next outlet/switch, and the third goes to the bulb itself.

So I presume that light fixture in the closet is mis-wired. Can someone tell me what to look for?

[Nate Nagel]

black goes to the hot terminal, or the center terminal in the socket (if it's an Edison base; I don't know about the new two-pin CFs.) White goes to the neutral, or shell of the socket. Ground goes to the case. Black and white should be touching nothing but what I mentioned above.

You *could* have a neutral fault to ground that wouldn't show up as anything unusual to a circuit breaker, but would to a GFCI.

good luck

nate

[Dave]

Swap the light bulb and see if the fault moves with it. Simple things first!

[RBM]

You may have a ground fault on the one light. You may also have an anomaly. Why do you have a ground fault protecting closet lights in the first place?

[David Nebenzahl]

On 7/26/2008 6:02 PM RBM spake thus:

Ackshooly, it's not clear that the lights, etc., are on the protected side of the GFCI outlet.

OP, can you tell us exactly how this whole deal is wired? You say that the GFCI outlet "shares the circuit" with two other outlets and two lights. This could mean one of two things:

1. That it "shares the circuit" in that everything is connected to the same circuit (i.e., connected to the same breaker in your service panel), but that the two other outlets and lights are *not* protected by the GFCI outlet.
2. That everything (the two extra outlets and two lights) are protected by the GFCI.

How to tell? Simple: the GFCI has two sets of terminals, one labeled "Line", the other "Load". If these other things (outlets and lights) are connected to the "Load" terminals, then they're protected by the GFCI. If not, then they're not.

This'll help a lot in diagnosing your problem.

[RBM]

He's already said that one closet light trips the GFCI. That's not going to happen if it's connected to the line side. The easiest layman test to see if an outlet, etc. is protected by a GF device, is to hit the test button on the device and see if it kills it

[John Grabowski]

I would start by removing the problem light fixture and just put a pigtail light socket in its place and see what happens.