A GFCI without ground wire isn’t ideal, but it’s better than a 2-prong outlet. A GFCI outlet will work without a ground wire and it’s legal. Here’s how to properly wire a GFCI outlet without the ground wire, and label it to meet code. If the outlet shorts out for any reason, it will still trip for safety, even without ground.
A GFCI without ground wire won’t protect a computer from static electricity, so you have to label it as such, but it will protect human life in the event of a short circuit. And, if your goal is to pass an inspection, an electrical tester will cause it to trip. Installing a GFCI is an acceptable alternative to the dangerous and illegal practice of a bootleg ground.
Safety first: Turn off the power at the breaker box. It’s not safe to work on an outlet with the power on. Plug a light or better yet, a television or radio into the outlet, turn the power on, then flip breakers until the light or sound stops. If you use a light, you may need a helper. This is why I like to use something that makes sound, like a radio.
Wiring a GFCI without ground wire
A GFCI outlet has two sets of terminals, one for the incoming line coming in, and one for the load, for chaining outlets. The load terminals will be covered with a piece of tape. On regular outlets all of them are interchangeable, but not on a GFCI.
If you have two wires, wire the black wire to the brass terminal. Wire the white wire to the silver one. Remember, black to gold, white to white. Leave the ground terminal on the GFCI unconnected. Reversing polarity is a code violation, so wire it properly.
If you have four sets of wires and don’t know which ones are hot, you’ll have to disconnect the outlet and separate the wires. Turn the power back on, then carefully use a multimeter to find the live wires. Connect one black wire to one white wire. If it measures 0 volts, try another combination until you find one that measures about 115 volts. Turn the breaker off, note the wires, then hook that wire pair up to the incoming pair of terminals. Connect the other pair, the load, to the load terminals.
Replace the cover plate, then turn the power back on at the breaker box.
Labeling a GFCI without ground wire
GFCI outlets come with a sticker that reads NO EQUIPMENT GROUND. After replacing the cover plate, stick one of those stickers on the plate. That way people know the outlet lacks a proper ground but is still a GFCI outlet with safety features.