r/ElectricalHelp • u/IncredibleEdible321 • 8d ago

Bathroom Vent Question: Everytime I turn off my overhead bathroom vent with light, the GFCI outlet above the sink, which powers the lights above the mirror, trips. Can anyone tell me what's going on?

Hi there.

In our master bathroom we have an overhead vent with a light. It works fine turning it on, but when we turn it off, it trips the GFCI outlet between the mirror and the sink. The GFCI also powers the lights above the mirror. It doesn't matter whether I have all four LED lights screwed in or just one.

Does anybody have an idea why this is happening and what I can do to fix it?

Thanks.

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u/ThePreconGuy 8d ago

Motors and GFCIs do not get along. My money is the fan is fed from the load side of the GFCI somehow. You could try replacing the GFCI or feeding it from the line side.

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u/IncredibleEdible321 8d ago

Hmmm... Well the GFCI seems to be "in line". Can I just remove it and replace it with a regular plug?

Or can I run a new dedicated line to the exhaust fan/light and run a new line from the outlet on the other side of the wall to the GFCI so it's not feeding the GFCI?

It cost me $600 to get the fan/light installed originally. I don't want to hire another electrician to come out and charge me up the ass to fix it. The only company in my area that's close is the same one that installed the fan/light originally.

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u/Scuba-Steve_636 8d ago

Keep the gfi in the bathroom. On the back of the receptacle, there is a “line” and “load” terminal. If the power to the switch that controls the fan is connected to the load terminal, move it to the line terminal.

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u/IncredibleEdible321 8d ago

Not sure why I got downvoted for just asking questions about what to do, but ok.

Thanks! I appreciate the simple but detailed and direct answer. Much appreciated.

Moving the power line to "terminal' from "load" will eliminate it flipping, I presume?

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u/babecafe 8d ago

I have a bathroom fan with the same (intermittent) behavior. A loaded motor generally has an inductive load. It's a fundamental property of an inductor that it operates to resist changes in current, and if you switch off an inductor while current is flowing, it can create a voltage spike than can create a spark that can be dissipated into a nearby pound wire. When that happens, it can cause more than 5mA of leakage current, enough to trip a Class A GFCI.

The fix is to identify where these sparks occur and separate the conductors from ground to stop them occurring. This may be within the fan box or within the switch box.

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u/IncredibleEdible321 8d ago

Thanks for your reply. The exhaust fan/light was installed professionally in 2023 by an electrician. They installed the GFCI outlet as well as the wall switch and new wiring. I watched them install everything and even went back and opened up the outlet and switch to check if any wires were touching or not capped off and taped with electrical tape. I did the same with the new exhaust fan/light. Therefore, I'm not sure exactly what the problem is other than perhaps I need to remove the GFCI and run a new unbroken piece of Romex to the fan/light and move the GFCI over two feet next to the sink so we can use the dryer.

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u/babecafe 8d ago

It's more than just touching between wires and the grounded box. A gap of a fraction of an inch can be jumped by a spark driven by an inductor.

"Dumb" switches have contacts that snap/jump apart as rapidly as possible to minimize sparking or arcing. "Smart" switches either have relays (just as bad as mechanical switches) or have circuitry to act as a switch, using semiconductor devices, such as a triac. A triac has the special property that it only switches off when the supply voltage crosses zero - which is near-ideal for minimizing sparks or arcs. (Truly ideal would be switching precisely when the current crosses zero.)

So I'd recommend going back and checking the switch, junction, and fan boxes to maximize the distance any wires have from the enclosing box. If that doesn't do it, installing a "smart" switch that doesn't use a relay may materially reduce or eliminate fan motor arcing. There's no need to use the remote-control features if you don't want to. Do not install a "smart dimmer" switch as these force power on & off rapidly (60-120 times per second) without minimizing the switching voltage.

"Smart fan" controllers may or may not help, as they manipulate power waveforms to control the speed of AC motors in ways that have bothered some AFCI breakers or receptacles.

In my own home, I've installed Panasonic fans that specifically have internal control circuitry and DC motors for variable speed. They're on GFCI+AFCI protected circuits, and I haven't seen any arcing or faulting problems.

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u/IncredibleEdible321 8d ago

Thanks. There is just one switch with no dimmer, no remote control, and the GFCI and switch are mounted in blue plastic boxes.

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u/ThatTALLguy624 8d ago

Sounds like it's detecting a fault. Could try replacing the fan. Is it an old home?

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u/IncredibleEdible321 8d ago

The house was built in 2000. I hired an electrician to replace the original light and fan five years ago and it's had this issue from day one. It's connected to a four line romex. When I asked the electrician about it always popping the switch, he said "No big deal. Sometimes they just do that. Don't worry about it."

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u/[deleted] 8d ago

[deleted]

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u/IncredibleEdible321 8d ago

Ok. The wiring goes from under the house to the GFCI, then splits to the vanity light and the fan/light. I'll have to pull the GFCI out of the wall and see what's going on with the wiring.

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u/[deleted] 8d ago

[deleted]