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GFCI Receptacle Trips When 3-Way Light Switches Are Turned On

Posted by ntl1991 (My Page) on
Sat, Aug 14, 10 at 22:57

Hello. I'm having a bit of a difficult time diagnosing what seems like a simple enough problem.

First off, I've been in the process of replacing 2-wire, non-grounding receptacles with those that are 3-wire, grounding-type in my late 1940's home. Of course, according to the NEC, I can only replace a 2-wire receptacle with a grounding type if it's protected by a GFCI. OK. So I installed a GFCI receptacle right at the beginning of the circuit. Now, when I turn on my two wall sconces above my fireplace (which are downstream of the GFCI), both controlled by a pair of 3-way backlit switches, the GFCI immediately trips. If, however, I remove the light bulbs from both sconces, the GFCI does not trip when I operate the switches. I'm absolutely confident that the GFCI receptacle is installed correctly with the hot and neutral wires (for both the line and load) in the proper location.
(Also something interesting... With the power on at the fusebox, and the GFCI on and working, the backlights in the 3-way switches are lit. BUT, when I remove both of the bulbs from the sockets, the backlights go out... Why is this?)

Now, Inside the switch boxes, I have the traveler and common wires, plus a spare, tucked back, unused wire in each box. The switches are wired correctly, and worked flawlessly when I had a 2-wire receptacle at the beginning of the circuit.

Now, it seems to me that the only other place that the problem can be coming from is the wiring for the light fixtures. When I removed both fixtures, the neutral wire from each fixture was connected to (what looks like from the bulge of electrical tape) a soldered splice of two wires. The hot wires from each light fixture is connected to a single wire coming out of each box.

I've heard that if the fixtures are wired using another circuit's neutral wire, this can cause the GFCI to trip. How could I determine if this is true?

Any help or advice would absolutely be appreciated.


Follow-Up Postings:

RE: GFCI Receptacle Trips When 3-Way Light Switches Are Turned On

The backlights work by leaking a small amount of current into the circuit when they are off. That's why the bulbs have to be there (and the back lights may not work when something other than a incadescent bulb like a CF is put there).

As for the GFCI tripping, again your analysis is correct, you need to find see if you can trace back the wire. One way to test (and this is only a test, do NOT leave the circuit this way), is to go to the GFCI and remove the load wires from it. Leave the neutral disconnected. Connect the hot wire to the line (bypassing the GFCI). If your sconces work, then for sure you're getting the hot from this circuit but the neutral from another.

RE: GFCI Receptacle Trips When 3-Way Light Switches Are Turned On

Thanks! I'll try that today and post my results.

RE: GFCI Receptacle Trips When 3-Way Light Switches Are Turned On

I didn't have time to diagnose the problem today, but I do have a question, though. Lets say that the neutral is, in fact, shared with, lets say, the dining room's circuit. I've read that I can back-wire the GFCI that I already installed by keeping the LINE wires in place from the fusebox, and back-wiring the "LOAD" wires to the LINE on the GFCI. This, of course, would provide no GFCI protection to the other outlets and the wall sconces. I can then install a GFCI in place of the downstream receptacles, bypassing the light fixtures and their shared neutral. If one of the receptacles in the room turns out to be "after" the lights, I can then wire the GFCI normally, and I won't need to use another GFCI for any receptacles downstream from THAT GFCI. Is this correct?

If so, my hope is that the lights aren't getting power from any of the receptacles, which would mean that none of the receptacles should be using another circuit's neutral. I think this is the case, though, because after I installed the GFCI (and before I tested the sconces & switches) I plugged a fan into all of the other receptacles downstream and they all worked. The GFCI didn't trip. If any of the receptacles were using another circuit's neutral, then when I plugged the fan in, they would've tripped the GFCI... Is my reasoning correct?

Thanks for the help.

RE: GFCI Receptacle Trips When 3-Way Light Switches Are Turned On

Yes, you can wire a GFCI just like it was a regular outlet (everything connected to the line side) and then the outlet itself is protected but nothing else.

Another option is that the lights could be fed from another circuit but at some point the two circuits (perhaps their neutrals) touch. Yet a third option is that the neutral is actually connected to the same circuit but to someplace before your GFCI receptacle.

One thing you could try (and I don't know what you've got for a main panel) is to either put a GFCI breaker in, or install a GFCI closer to the main panel.

RE: GFCI Receptacle Trips When 3-Way Light Switches Are Turned On

I'll be investigating all of these options today. The one that sounds like a definite possibility is the third option where the neutral for the lights is connected before my GFCI receptacle.

After finding out that the GFCI was tripping when I'd turn the sconces on, I took the fuse out for that circuit. (I have a Federal Pacific Fuse Panel, by the way) I had to leave, and left the fuse out overnight. I went back the next day and realized that the front hallway light and the outside lights beside the front door weren't working. They are on the same circuit as the living room. But, when I put the fuse back in, they weren't affected by my tripping of the GFI. So, while I thought the living room outlet where I installed the GFI was the first device on the circuit, it's actually the front hall light or exterior lights.

Perhaps the sconces are getting neutral from the front hall light? I did notice that inside the box for the first sconce, I had a set of wires coming DOWN inside the box... This was odd to me because I have no overhead light in the living room.

For a little bit of reference, I uploaded the floor plans I made of the house. The fuse box is in the basement, located in the SW corner in the plans. The circuit we are talking about covers the Front Entry Lighting, Living Room Receptacles, Living Room Sconces, Dining Room Outlet, and Dining Room Overhead Light.


Here is a link that might be useful: Floor Plan of Home with Electrical

RE: GFCI Receptacle Trips When 3-Way Light Switches Are Turned On

OK. So I went and removed the LOAD neutral from my GFCI, and switched the LOAD hot to the LINE hot. Turned the power back on, and the lights did NOT work... Hmm. So I wired it without using LOAD, and then replaced all of the other outlets in the room (2 more) with GFCIs. I couldn't even wire one GFCI using the LOAD terminals, because all of the other outlets were missing a neutral for the load. The wires were tucked back in the box and clipped. 3-wires for each receptacle... But, now each GFCI is protecting itself, and nothing else; my wall sconces work properly with their three-way switches. Everything is safe and correct.

Thanks for all of the help, I really do appreciate it.


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