I am adding a circuit to feed off a live GFCI outlet. At the outlet I read 118V in both receptacles and the reading is stable. With the new cable, I connected the neutral white to the silver screw directly underneath the old one, and the hot black to the gold screw directly underneath the live one. When I go to test the exposed wires on the other end (not connected to an outlet yet), the voltage readings are crazy and bounce all around from 80V to 640V. Did I wire the new circuit to the GFCI incorrectly?

  • What does your multimeter read when 1) you touch the probes together and 2) when the probes are not connected to anything? This sounds like your meter is just spitting out random numbers when it's not reading anything. Please also post your meter make/model, the setting used, and ideally a picture of your meter and its settings.
    – Freiheit
    Jul 13, 2020 at 16:45
  • Did you actually want the line extension to be GFCI protected off this GFCI, or did you just grab those screws because they were the only ones open? Jul 13, 2020 at 18:43

2 Answers 2


One set of terminals says line that is the incoming hot. The other set of terminals that normally has a cover over them say load. The load is for additional receptacles to be protected.

Some brands the line is on the bottom some line is on top so we don’t know if it is correct or incorrectly wired.

Strange readings on your meter are you sure it’s on Volts and not millivolt range. Just wiring wrong cannot create higher voltage.

  • Yeah, there is no way to actually get 640V on a 120V circuit... Most likely you have your meter on Autoranging and it is reading millivolts, but you are not noticing that on the display because you got freaked out by seeing the 640 number. 640mV = 0.64V
    – JRaef
    Jul 13, 2020 at 17:09
  • 1
    Worse thing home Depot did was to start selling meters..lol+
    – JACK
    Jul 13, 2020 at 17:20

Definitely not a multimeter problem. I opened it up again to make sure that I wired the new cable to Load, which I did do correctly. I removed the hot in order to turn it around to read and make sure. Then I wired it again as before and it now the new cable reads a stable 118V. Only thing I can think of is an intermittent short after I screwed it back together, but that doesn’t make sense since it’s a GFCI that tests correctly, and of course the breaker itself. Anyway it’s all taped up now and it appears to be solved. Thanks all!

  • Yeah, sometimes you don't get the connections quite tight enough. That's what AFCI breakers protect against - Arc Faults. It's also why all electrical wiring devices come with torque specs and why you should tighten things to spec. You say "it's all taped up" - there shouldn't be any need for any electrical tape in a junction/fixture box, unless you're identifying wires... Also, please give yourself a check mark so others know that this is resolved.
    – FreeMan
    Jul 13, 2020 at 17:07
  • @FreeMan Some DIY sites suggest taping over the screws on the side of the outlet to better insulate them. DIYers painting a room can get sloppy with the paint brush and slip into the outlet and hit the hot screws if not insulated. Also, I solved a true short problem when, after years of plugging and unplugging things into a switched outlet, somehow the bare ground wire contacted the hot side screws and tripped the breaker every time the outlet was switched on. Had the screws been taped over, that wouldn't have happened. Even so, I personally don't tape over the screws. Jul 13, 2020 at 17:16
  • And, somebody down voted without indicating why. Nice... :/ Reinserting the wires and retightening is a perfectly reasonable thing to do, and if the connections were loose to begin with, would solve the issue.
    – FreeMan
    Jul 13, 2020 at 17:21
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    @FreeMan Now now, play nice. It's not a bad practice to tape over the side screws, not like taping over wire nuts to hold them together (that's a stupid idea). To each his own. I don't tape the screws but won't criticize those who do. Jul 13, 2020 at 17:31
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    @FreeMan I recently taped over the screws of a GFCI outlet that I had to fit into a single gang mud ring with a box entender... First time ever for taping.. and I have a clue... You'll see lots of DVs without reasons... hate that and I've never DV... just had comments on what's wrong.
    – JACK
    Jul 13, 2020 at 17:34

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