This has been going on for awhile, but it is intermittent – about every 3 – 8 times the fluorescent light in a closet off the bathroom are turned off, one of the two GFCI outlets in the bathroom will trip. 95% of the time, it is one particular of the two GFCI outlets in the bathroom. The fluorescent light will still turn on with the GFCI tripped. This will also happen – about every 3 – 4 times – with fluorescent lights in my garage. The lights there will also still work with the GFCI tripped.
The bathroom GFCIs seem easily tripped by what I am 99% certain are non-faulty appliances (hair trimmers, electric tooth brush, etc…)
Ideas? Thx!
Best Answer
Anytime a thing on circuit 1 trips a thing on circuit 2, you have a crossed neutral. That's bad wiring. On ground wires, it is ok to just twist all the grounds together (if they're all from the same panel) even if they are different circuits. Some people think they can do the same with neutrals. That was always bad... and with GFCIs, it does not work.
Another sign of sloppy work is two GFCI receptacles on the same circuit. Occasionally a wiring topology makes this semi-necessary, but usually it means the installer does not understand how to install GFCI's.
What's happening with the crossed neutrals is that current to an appliance, now returning to source, has a choice of two directions: directly on circuit A's neutral, or through a GFCI device on circuit B's. Actually, it follows all routes at once, in proportion to their conductivity (1/resistance). That conductivity is influenced by loop effects and eddy current heating, because those occur at the cost of conductivity: in short, it prefers to go back the way it came. That still means some current is going the wrong way, and that will still tend to trip a GFCI.
So you need to untangle those neutrals.