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I put up some Christmas lights outside a few days ago and everything seemed to work fine for the first 2 nights. On the 3rd day, the lights came on for a bit, then went out and I couldn't get them back on. I tried different timers, cords, resetting (GFCI) breaker downstairs, etc. I used an outlet tester and it lit up as an Open Neutral.

I replaced the outlet, which still didn't help, so I tried figuring out the circuit by following wires in the basement. Here's what I came up with (note this seems to be its own standalone circuit that shares a GFCI breaker with another outdoor outlet and the bathroom outlets in our house):

switched outlet

I think this looks like a standard switch loop. The switch's ground wire threw me off at first, since it's not pigtailed into the outlet's ground and is just wrapped around the outside of the casing. I don't have a multimeter, just an outlet tester and a voltage tester:

voltage tester

When the switch is off:

  • The outlet tester has no lights lit
  • The outlet has no voltage differences across any terminals
  • The switch shows no voltage differences across terminals (shouldn't it?)

When the switch is on:

  • The outlet tester shows Open Neutral
  • The outlet has 120V between Hot and Ground, no voltage diff between Hot and Neutral
  • The switch shows no voltage differences across terminals (expected)

I also looked inside the electrical panel and didn't see any obviously loose/disconnected wires.

I don't understand why the switch doesn't show any voltage differences when off, but it is obviously doing something because it still affects the outlet.

What's my best next course of action/investigation?

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  • At switch you are not reading difference between two wires(hot and neutral/ground), you are reading two sections of the same wire. Open/broken neutral could anywhere in that circuit coming from the breaker. Other outlets or junction boxes, or worst case for finding a broken wire. You did also check the lights themselves if they are working still? Turn off breaker and check all neutral connections on that circuit, broken neutral not good.
    – crip659
    Nov 30 '21 at 18:51
  • With the switch ON and lights plugged in... check voltage from neutral to ground, everywhere you can. (obviously you won't be checking to ground at the switch, but neutral doesn't go there anyway.) Anywhere neutral measures 120V from ground, you are on the far side of the wire break. Also "visual inspection" of wires in panels won't reveal much. Unscrew the wire from the terminal, remove it, inspect it, inspect the lug, then reinstall it (on a different lug if possible) and torque to spec. Expect it to be hot, because neutrals can be hot. That's why we insulate them. Nov 30 '21 at 19:06
  • Also note on those 3-light testers, peel the label off and throw it away. The red-yellow-yellow lights are great. The label is extremely misleading in every failure case except open neutral. The label is tuned to identify wiring errors in new construction... not wiring failures (of correct wiring) in old work. Nov 30 '21 at 19:11
  • So the thing that makes it hard to check voltage between neutral/ground everywhere is that, as far as I can tell, the neutral is a single wire from panel to outlet (see diagram, no wire nut in the junction box for neutral), with the only splice being a pigtail of the neutral to other neutrals inside the panel for the same breaker. There are other outlets on the same breaker, but not this specific "run" of wire. This is the only outlet showing Open Neutral. Could the others still be causing some issue? Nov 30 '21 at 21:55
  • Well, I was able to fix it. It turns out that one of the GFCI outlets on the other side of the house (connected to the same breaker) was wired wrong, with 2 sets of wires going to the Line side and 1 set going to the Load side. I got that sorted out and everything started working/testing correctly again. Thanks all! Nov 30 '21 at 23:43
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Well, I was able to fix it. It turns out that one of the GFCI outlets on the other side of the house (connected to the same breaker) was wired wrong, with 2 sets of wires going to the Line side and 1 set going to the Load side. I got that sorted out and everything started working/testing correctly again. Thanks all!

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