I have a relatively old house, built in the 1950s. I am slowly updating it to have smart switches etc., but the existing electrical wiring is fairly haphazard. Just yesterday I replaced a dimmer switch and found that the white wire pigtail in the box was in fact hooked up to hot, not neutral. Fortunately when I turned on the circuit it tripped the GFCI before doing any damage but I wonder if there's a better way to avoid this in the future.

Currently I just turn off the circuit at the breaker and verify there's nothing live in the box with a non-contact tester (and then an insulated screwdriver, just to be sure). Should I be pulling the wires out, switching the circuit back on, and then testing each wire individually with a multimeter (sometimes the nc tester gives false positives) before doing any work? And if I do find a wire incorrectly colored, is there a good way to label it as such?

Also, what would have happened if the switch I talked about above hadn't tripped the GFCI? When I turned the circuit back on, would the breaker immediately switch it off, or would there be a fire hazard?

  • 2
    Learn what a switch loop is. That probably won't be the only one you find. diy.stackexchange.com/questions/31700/…
    – Ecnerwal
    May 12, 2019 at 20:39
  • 2
    In short, it will not be unusual to find that many of your switch locations will not support a smart switch without rewiring the building, as they will not have ANY neutral conductor provided. That was the way it was done for a long time, and it was code until 2011. They should be re-marked black or red, but they often are not in practice, or it wasn't very permanent after all.
    – Ecnerwal
    May 12, 2019 at 20:49
  • First of all, id the related light controlled from more than one location? If so, check this out (any time the white wire is used as hot it should be wrapped with black tape inside the box! www2.familyhandyman.com/electrical/wiring-switches/…
    – Larry Birt
    May 12, 2019 at 21:20
  • What country are you in? Wiring and its colours differ regionally.
    – Stilez
    May 13, 2019 at 2:14
  • @Stilez WA, USA
    – MooseBoys
    May 13, 2019 at 7:18

1 Answer 1


North American view, since OP is there.

Wires in electrical wiring are NOT color coded

Your mistake there was assuming white meant neutral. The simple fact is that electrical wiring is not color coded. That's because cables are manufactured with only one set of colors - black and white for /2 cable or black, white and red for /3. No matter what function the wire has, it must "make do" with the colors available in standard cable.

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Any colors you want, as long as you want black, white and maybe red.

There are only 2 color rules.

  • Grounds are always and only, green, yellow-green or bare. Those colors can only be ground.
  • Neutrals can only be white or mid-gray, but that only applies if this cable has a neutral. If this cable doesn't need a neutral, white can be a hot. You're supposed to mark it with paint or tape, but previously you could skip it if the usage was "obvious". (to an electrician, heh).

This last one is what bit you.

Smart switches have special needs

You should have opened up your switch and investigated the wires that were available to you, before you bought the switch. If you only see 2 wires (besides ground), they must be always-hot and switched-hot, because a switch can't work without those two.

If your location doesn't have neutral, don't buy a smart switch that needs it.

If your location doesn't have ground, ditto.

You may hear things that tempt you to use ground for neutral or vice versa. Don't. Neutral is not ground.

There are smart switches that require neither neutral nor ground. They may require at least one of the bulbs to be compatible LED, incandescent, or a capacitor-resistor bypass added.

There are also other ways to work around the problem, such as smart switches that put a switching module up in the ceiling rose, then the wall switch effectively becomes a "remote" for the module.

  • As far as I know electrical wiring is colour coded. However the codes change over the years as do the colours. For example in The Netherlands the colour coding is: hot/live: brown (in 3-phase brown/black/grey), neutral: blue, switch wire: black and ground: striped yellow/green. Before the 1970's this used to be: hot/live: green (in 3-phase green/black/blue), neutral: red, switch wire: black and ground: either grey or white. So as you can see if the house was wired up with an older coding the current usage could vary. May 13, 2019 at 7:36
  • @yetanothercoder OP is clearly in North America from terminology, sorry for not adding a disclaimer to that effect (just what the world needs, more disclaimers). "as far as you know"? If you look hard at switch loops, 2-ways and other specialty wiring in your home country, you'll find it's true there too, regardless of color changes. May 13, 2019 at 15:14
  • Helpful answer, but can you elaborate on what I should be doing to check whether a wire is hot/neutral/switched, if wire color is an unreliable indicator?
    – MooseBoys
    May 13, 2019 at 20:34

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