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I am replacing "razor only" receptacles to GFCI. The outlet contains a LINE cable (black, white, bare copper). The previous receptacle of course did not use three prongs, so the ground was just secured to the outlet box's grounding terminal (screw).

To install the GFCI according to the instructions, I need two new pieces of wire for the ground pigtail: one to the grounding terminal, and one to the receptacle's ground. See diagram below.

My small problem is that I don't have green or bare copper wire. I have suitable 6" 14 AWG wire scraps from the old receptacle, but they are white or black.

  • Would it be terrible if I used the wrong colors to make the pigtail? Electrically of course there's no problem. Potential confusion is the only issue I can see, but since it would all be in the same outlet box, maybe that's less of a problem?

  • It also occurred to me to strip the black/white insulation and thus have bare copper, but it is stranded (all the wires from LINE are solid), so that seems like a bit of a mess. Is that even ok to do?

grounding instructions

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  • You can strip the wire if it's being used for ground. Or wrap it in green electrical tape.
    – Nate
    Sep 28, 2019 at 3:06
  • Can't find anything saying bare stranded wire is a problem. I've installed light fixtures that include a bare stranded ground wire.
    – Nate
    Sep 28, 2019 at 3:13
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    @Nate Wouldn't a 6" bare stranded wire get messy? I'm not sure how many strands there are but it's a lot, as in probably dozens.
    – adatum
    Sep 28, 2019 at 3:33
  • @adatum -- it's going to be either 7 or 19 strands, not "dozens" unless it's fine-stranded wire, which isn't generally used for mains work
    – ThreePhaseEel
    Sep 28, 2019 at 3:37
  • It will be twisted on one end by a wire nut, and clamped to a screw terminal at the other end, and only be a few inches long. I wouldn't worry about it being messy. You can always wrap some electrical tape around it if you find it too messy to work with. Or you can always run to the hardware store for some green #12 THHN, it's less than 10¢ a foot here
    – Nate
    Sep 28, 2019 at 3:41

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The answer to your question is "quite critical": Grounds must be green, yellow/green or bare. Neutrals must be white or gray. All others are hot.

Binding stranded wire to a screw terminal is tricky. Not impossible but tricky. I like to "super-twist it" by gripping the wire in a hole intended to shear off bolts, which keeps it circular. You have to have just the right touch to clamp the wire enough to hold it without shearing it.

Because of the difficulty for a novice to attach stranded wire to a screw terminal, I would advise either going to the shop and getting some solid #12 wire, or, you can use round crimp terminals for the ground screw on the junction box (not on a receptacle).

If you have wire whose insulation is not green or yellow-green, there are two ways to mark it as a ground.

  • Strip all the insulation off. Optional: wrap it with green tape, which will solve the birdcaging issue if the supertwist doesn't.
  • Don't strip the insulation off and totally obscure it with green tape. However this violates Code.
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  • Thanks for the tips. I did notice that half of the strands tended to "squish" out from under the screw head when I tried it previously. Is the pigtail in the instructions necessary? eg. would it be ok to keep LINE's solid ground wire at the screw terminal and add another wire from the screw terminal to the receptacle's ground? Exploring this left me lacking confidence in how securely the screw could hold more than one wire (especially with the addition of the stranded one), not to mention questions of Code.
    – adatum
    Sep 28, 2019 at 4:29
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    @adatum putting more than one wire on a screw is absolutely forbidden anyway. Unless you use round crimp terminals, but you quickly find you would need to get 5 fingers and 3 thumbs inside the hole while also holding a screwdriver :)
    – Harper - Reinstate Monica
    Sep 28, 2019 at 4:36
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    @Harper -- wiring device screws aren't rated for use with ring or spade terminals anyway...
    – ThreePhaseEel
    Sep 28, 2019 at 4:49
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    @ThreePhaseEel I assume adaturn is talking about the ground screw in the back of the box. Yes, agreed, on a receptacle that won't do.
    – Harper - Reinstate Monica
    Sep 28, 2019 at 4:53
  • Yes, I meant the ground screw in the box. "absolutely forbidden".. good to know, and even better to know the reasons. I think I have some solid copper wire (with grey insulation) but I'll need to check the size. As for crimp terminals what do I need to know? I might have some lying around but I know nothing of types and sizes and I'm not looking to create fire hazards.
    – adatum
    Sep 28, 2019 at 5:04

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