Many older homes have electrical outlets, or receptacles, with only two slots for a two-prong plug, and lack a third slot for the grounding prong found on most modern appliances. A two-slot outlet often indicates that the home's electrical system, most likely, does not have ground wires for the outlets, switches, or other devices. Instead, there may be a grounding system that works via metal electrical boxes and conduit.
Two-slot outlets are perfectly legal (and generally safe) in existing homes. However, in wet locations like bathrooms, you need more protection than just a ground wire. That's where a ground-fault circuit interrupter, or GFCI, comes in.
A GFCI outlet has an internal breaker that can shut off the power to the outlet in the event of a ground fault, which is most likely to occur when there is water around. GFCI outlets are also wired with a switch that can be reset should the circuit trip. GFCI-protected outlets are required in all bathrooms (in new homes and remodels).
If you'd like the same protection, but you have the old-style outlets, you can simply swap them out for new GFCI outlets to get full outlet protection. Just be aware that the new outlet will not be fully grounded on the circuit, even though it contains the third slot for three-prong plugs.
What Is a GFCI Outlet?
A GFCI (Ground Fault Circuit Interrupter) outlet—also known as a GFI outlet—is an outlet that monitors the balance of electricity that goes through a circuit. In the event of a short, GFCI outlets cut off the electricity to the outlet, preventing damage to the circuit.
GFCI Wiring Configurations
GFCI outlets can be wired in a couple of different ways. If you're just replacing one outlet in the bathroom, use the single-location method, which provides protection at a single GFCI outlet. A GFCI outlet wired in this way does not have to be on its own breaker.
The other method is called the multiple-location method. This procedure requires GFCI outlet wiring in series, and provides protection to any additional outlets (including standard outlets) "downstream" on the same circuit. Multiple-location wiring requires two circuit cables in the electrical box—one for power coming into the outlet (marked with the word LINE on the backside) and one for power going out to the other outlets (marked with the word LOAD on the backside).
Single-location wiring is demonstrated in this article. If you want to use multiple-location wiring, consult the manufacturer's GFCI outlet wiring diagram and instructions, and make sure to also fully understand GFCI wiring loads for your line.
Equipment / Tools
- Non-contact voltage tester
- Neon circuit tester (optional)
- GFCI receptacle outlet with cover plate
How to Wire a GFCI Outlet
Turn Off the Power
Turn off the power to the circuit feeding the old outlet by switching off the appropriate breaker (or removing the fuse) in your home's electrical service panel (breaker box). Go back to the outlet and use a non-contact voltage tester to confirm that power is off.
Remove the Old Outlet
Remove the screw holding outlet cover plate, and remove the cover plate. Double-check for voltage by touching the voltage tester to each side terminal on the outlet.
Remove the two small screws holding the outlet to the electrical box. Gently pull the outlet out of the box, being careful not to damage the old wiring. Unscrew the the black and white wires from the outlet terminals, pull off the wires, and remove the outlet.
Confirm Adequate Space in the Box
Make sure there's enough space inside the box for the relatively large body of the GFCI outlet. Some old outlet boxes are small, and some are jam-packed with wires; you want to make sure the new outlet will fit. Do this by gently pushing the wires back into the box and test-fitting the GFCI. if the new outlet fits without a struggle, you can proceed with the installation. If it doesn't fit so well, you will need to have the box replaced with a larger box before installing the GFCI.
If there are extra wires in the box, test each of them for voltage before touching them. Sometimes outlet boxes are used as junction boxes and may contain wires that are not controlled by the same circuit breaker as the outlet wires. This means the extra wires could be energized.
Install the GFCI
Look at at the back of the GFCI outlet; you will find four terminals: two are marked "LINE," and two are marked "LOAD." The LOAD terminals are typically covered with tape because you don't use them for single-location protection, as shown here.
To connect the outlet, connect the black wire to the brass-colored LINE terminal, and tighten the screw securely. Connect the white wire to the silver-colored LINE terminal screw, and tighten it securely. Gently fold the wires and tuck them back into the box while pushing the outlet into place. Secure the outlet to box with its two mounting screws.
Add the Cover Plate and Test the Outlet
Fit the new cover plate over the outlet and secure it with the provided screws. Restore power to the circuit by switching on the breaker in the service panel.
Make sure the RESET button on the face of the GFCI is pushed in. Then, press the TEST button; the RESET button will click and pop out; this shuts off the power to the outlet. Press the RESET button again to restore power.
If desired, you can test the outlet with a neon circuit tester for proper wiring. Sticking one tester probe into the long (neutral) slot and one into the short (hot) slot should make the tester light up, indicating there is power. Next, insert one probe into the short slot and one into the ground slot; the tester should light. If it does not, stick one probe into the long slot and one into the ground slot; if the tester lights up, the outlet is wired backwards (the neutral wire and hot wire are connected to the wrong terminals, and the outlet should be rewired).
Is it better to use a GFCI outlet or breaker?
It depends. You should use a GFCI outlet if you want to protect individual outlets. And you should use a circuit breaker if your aim is to protect the electrical system, as a whole, from ground faults.
What should not be plugged into a GFCI outlet?
Do not plug large appliances, like a refrigerator, a freezer, or a sump pump, into a GFCI outlet. And while it's okay to plug in a light, if the circuit trips, you may find yourself in the dark.
Can you have 2 GFCI outlets on the same circuit?
You can house two GFCI outlets on the same circuit. However, if one has an issue—similar to a string of Christmas lights—all of the other outlets down the line will fail.