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I installed a GFCI in a bathroom that seems to trip when I turn on the hall light, which has 3 separate switches? I looked at the outlet box closest to the one light switch under the premise that this feeds (in the loop) the light (switch) source. The outlet box has one black and 2 white wires attached. Is this normal? Is the second white wire causing the feedback from other power circuits controlling the same light?

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    Are you asking us if the hall light has 3 separate switches? We wouldn't have a clue... Since you're comfortable enough opening up boxes, please pull all the devices out of the the wall without removing any wires and get clear focused pictures of them, then edit these pics into your post, including a description of where in the scheme of things the device falls and your best guess as to where the wires go. Without that, it's really hard for us to do anything but guess right along with you.
    – FreeMan
    Commented Dec 16, 2021 at 14:03
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    This makes no sense at all. Either you have conduit - in which case white should never get retasked as something other than neutral and then 2 white + 1 black has no purpose I can think of. Or you have cables, in which case there is another black lurking somewhere. Upload pictures showing all wires/cables - both attached to switches and receptacles and showing where they come into the box - for both the switch box and the receptacle box. Do not disconnect any wires - just turn off power, pull the switches and receptacles out, take pictures.
    – manassehkatz-Moving 2 Codidact
    Commented Dec 16, 2021 at 14:03
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    @manassehkatz-Moving2Codidact it's almost like we've done this before! ;)
    – FreeMan
    Commented Dec 16, 2021 at 14:08
  • You looked in "the" outlet box, it sounds like that is an outlet in the hall right? Not the bathroom outlet that is tripping but a different one? One black and two white wires is not normal. But let's focus on the bathroom first. How many cables and wires are in that box, and how exactly did you connect them? Feel free to add clear, focused, well-lit pictures of the bathroom outlet wiring by clicking "Edit" above and pasting them in.
    – jay613
    Commented Dec 16, 2021 at 20:39
  • Can you post photos of the insides of the boxes involved please?
    – ThreePhaseEel
    Commented Dec 17, 2021 at 2:41

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Receptacles have 2 screws on each side, and the 2 screws are directly connected to each other (if you don't break off the tab). So you can use the 2 screws as a handy method to do splices. It's easy to fall into that as a habit.

Enter GFCI. They also have 2 screws on each side. But they're not the same. One screw on each side is "Line" (you probably figured out the GFCI won't work unless the supply is connected to this one)...

...but then, what do you do with the extra wire(s)?

If you lapse into "well just put them on the extra terminals because that's what I've always done", then this happens.

You are better off putting ALL wires on "Line" unless you are an expert on using "Load". As for attaching 2 wires to "Line", read the GFCI instructions, they specify a way to do that. Beyond that, pigtail all wires to LINE.

Over-use of "Load" results in accidentally protecting other parts of the circuit, at best. What's wrong with that? A receptacle goes dead, person doesn't know why, person calls electrician. Electrician charges $150 to show them a GFCI receptacle that has tripped. Code/instructions require you mark each protected receptacle "GFCI Protected" - for this reason!

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