Electrical - GFCI tripping

Question

I was replacing an outlet in my bathroom with a gfci outlet. When I throw on the power, it trips but not only that, it takes out a set of lights over the mirror which are connected to a double switch on the wall. The other switch is fine. What should I be looking for to fix this issue?

Answer 1

Because "continuing the circuit" is a completely different thing than "placing a load inside the GFCI's protected zone". Especially where switches are present!

I get it. You've installed receptacles for decades. You know (other than split receptacles) the extra 2 screws on the receptacle are for continuing the circuit onward.

Now you also know there are some receptacles (eg. USB) that only have 2 supply terminal screws. They do not provide any method for continuing the circuit onward. With those, you are forced to pigtail the receptacle and use a wirenut to splice its supply with the onward wires.

GFCIs are like that too, GFCIs only have two supply screws. They are conspicuously marked LINE and they are the only terminals not covered with warning tape. (The warning tape says, in so many words, "For Wizards Only".)So, similar to a USB, these should be pigtailed with a wirenut for continuing the circuit onward. Only the LINE terminals should be used. This is especially true in a retrofit situation like this, and double especially when there is a switch in the same box.

Everything I have said so far is about continuing a circuit onward, which is what you are trying to do. Now we're going to turn the page.

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GFCi devices come in several packaging styles. There,s the GFCI+breaker, the plain GFCI deadfront, and our friend the GFCI+receptacle. All of them provide a "GFCI protected zone". Obviously, on a GFCI+receptacle, the protected zone is the built-in sockets.

However, all of them can extend their zone of protection beyond the device itself. (That'd be kinda necessary on the breaker and deadfront, eh!?) How to do that is beyond the scope of this answer. But you may know a rule that currents must be equal in any cable. That rule applies in spades to any GFCI zone of protection. This makes it rather tricky to work with them in switch boxes.

However there's generally no value or benefit to putting hardwired bathroom lights, fan, heater etc. on a GFCI.

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Bottom line, pigtail everything to LINE and call it good.

Answer 2

I am afraid I have to respectfully but strongly disagree with the idea that removing the load from the GFCI protection is an acceptable solution. That's along the lines of putting black tape over the OIL light on your car's dash so you don't have to deal with the irritating red glow. It's better to at least try to figure out what's going on and see if there's a potential hazard.

There's a reason GFCI protection is required in bathrooms, it's a place where faults are more likely to be dangerous due to proximity to water and plumbing. GFCI's trip levels are tiny but so are the actual voltages that can harm a person. Even a mind jolt in the bathroom can be dangerous - even if the zap doesn't do much damage, the fall might.

I'd first test the receptacle itself. Temporarily remove the load wires and cap them, and see if the GFCI will hold with no load. If it holds, plug in a load - something simple like a lamp - see if it holds. If it holds, see if it trips as it should with a GFCI receptacle tester. (If you have solenoid voltage tester, you can also test a GFCI by testing voltage from hot to ground - the load of the solenoid should trip the GFCI.)

At that point I'd replace the load wires and see if the GFCI still trips. If so, disconnect and cap off the downstream loads one by one. If you determine one of the loads is leaking voltage, you can decide whether to replace it or run it without GFCI protection.

If it trips with all the loads disconnected, that points to a wiring fault, which is bad news - it may be difficult to track down - but it is potentially dangerous, and should be corrected.