Some receptacles are configured to be “switched” and there may be “extra” wires in the box for that function. If the receptacle is intended to be “half-switched”, meaning one outlet is switched and the other is not, you cannot use an ordinary GFCI receptacle in that location. Contact a qualified electrician to complete the work if you have identified more than 4 loose wires (not counting grounding wires) or more than 2 cables, or for switched receptacles.
Power supply wires are connected to the line terminals, while load terminals help connect other outlets to the GFCI-protected device. [6] X Expert Source Daniel StoescuMaster Electrician Expert Interview. 16 August 2021.
Leave enough wire to allow the receptacle to be pulled at least 4 to 6 inches from the box.
Many electricians wrap the receptacle with a layer of insulating electrician’s tape to protect the terminals from accidental contact with metal objects.
There are many ways to determine which cable is the “supply”, using various test instruments (contact, non-contact, meters, etc). The following technique is for those who are unfamiliar with such things or who do not wish to touch the wiring while it is “live”.
If no power comes on in the receptacle, your capped wires are probably the “line” wires or your main power wires, assuming they are working properly. You may also want to test the capped wires to make sure the GFCI will have power before proceeding. You may do this with a separate tester or by repeating the previous testing steps with the cables swapped.
Many electricians wrap each receptacle with a layer of insulating electrician’s tape before reinstalling them into a box, especially a metal box. This provides another layer of safety from accidental contact with live parts.
If the device does not light up, you need to find out why before proceeding.
Be sure to mark the additional outlets to show they are “GFCI Protected”, using stickers that come with the GFCI receptacle. If you intend to work on more than a few of these, you may want to obtain a handy “outlet polarity and GFCI tester” at the home improvement store. It plugs into the GFCI and has lights that confirm power is on, the proper wiring polarity and ground, and may be obtained with a GFCI test button to verify the GFCI mechanism operates in each downstream receptacle. Note that a GFCI tester plugged into a receptacle without a properly attached grounding wire will not trip the GFCI because the tester is designed to “leak” a test current to ground.
The GFCI breaker has a protected “hot” conductor, a separate neutral connection, as well as a test and reset button. It will protect all devices on that entire branch, if properly installed.
