How to Wire a GFCI Outlet: Step-By-Step

Replacing 2-Prong Outlets With GFCI and Wiring GFCI in a Series

By
Bob Formisano
Bob Formisano
Bob Formisano is a licensed architect and builder with nearly 40 years of experience building new homes and restoring older homes. One of his specialties is repairing old systems dating back to the 1920s, including galvanized water pipes, knob-and-tube wiring, and more. His home repair articles for The Spruce span more than 10 years.
Learn more about The Spruce's Editorial Process
Updated on 11/02/23
Reviewed by
Larry Campbell
Larry Campbell
Reviewed by Larry Campbell
Larry Campbell is an electrical contractor with 36 years of experience in residential and light commercial electrical wiring. He worked as an electronic technician and later as an engineer for the IBM Corp. He is also a member of The Spruce Home Improvement Review Board.
Learn more about The Spruce's Review Board
2 prong outlet with GFCI wiring touched by hand

The Spruce / Kevin Norris

In This Article
Project Overview
  • Total Time: 15 mins
  • Skill Level: Intermediate
  • Estimated Cost: $12

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. Those two-slot outlets indicate that the home's electrical system does not have ground wires, and while they are perfectly legal (and generally safe), you need more protection than a ground wire in wet locations, like a bathroom. That's where a ground-fault circuit interrupter, or GFCI, can shut off power to the outlet in the event of a ground fault. 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 outlets are also wired with a switch that can be reset should the circuit trip.

GFCI Wiring Configurations

GFCI outlets can be wired in a couple of different ways using a single-location method or a multiple-location method. 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).

Both are easy DIY electrical projects, as long as you take necessary electrical safety precautions.

How to Test GFCI Outlets

What You'll Need

Equipment / Tools

  • Non-contact voltage tester
  • Screwdrivers
  • Neon circuit tester (optional)

Materials

  • GFCI receptacle outlet with cover plate

Instructions

How to Install a GFCI Outlet to Replace 2-Prong Outlets 

Materials and tools to upgrade a 2 prong outlet with a new GFCI

The Spruce / Kevin Norris

20 Top Tools You May Need for Electrical Projects

  1. 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.

    Circuit breaker switch turned off in home service panel

    The Spruce / Kevin Norris

  2. 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.

    Old electrical outlet gently removed from wall box

    The Spruce / Kevin Norris

  3. Confirm Adequate Space in the Box

    Make sure there's enough space inside the box for the relatively large body of the GFCI outlet. Gently push the wires into the box to test-fit the GFCI. If it fits easily, you can proceed with the installation. If it doesn't, replace with a larger box before installing the GFCI.

    Wires pushed back gently in electrical box to test-fit the GFCI

    The Spruce / Kevin Norris

    Warning

    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.

  4. 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.

    White wire and silver-colored line wire secured tightly in screw terminal in GFCI outlet

    The Spruce / Kevin Norris

  5. 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).

    GFCI outlet cover plate reinstalled and tested with reset button by screwdriver

    The Spruce / Kevin Norris

    Your GFCI outlet will come with a little sticker that says "No Ground," "No Equipment Ground," or something similar. Place this sticker on the face of the GFCI to alert people that the outlet is not grounded.

How to Install a GFCI Outlet in a Downstream Series 

  1. Turn Off Power, Test, and Prep

    The first steps in this process are simple but critical. Turn off the breaker that connects to this outlet, then test the outlet with a circuit tester to make sure you turned off the right one. When you've confirmed the power is off, remove the cover plate and disconnect the wires.

  2. Determine Which Wires are Hot

    Once you've disconnected the wires from the outlet, determine which are the power supply "LINE" wires and the downstream "LOAD" wires. Separate the wires, then use a circuit tester to test for a hot wire. The hot wire is the LINE wire. Turn the power back off.

  3. Connect the Wires to the Correct Terminal

    Re-strip and connect your LINE wire to the LINE terminal, and the downstream LOAD wires to the LOAD terminal. Typically, a white wire connects to a silver screw, while black connects to brass. Ground wires connect to green.

  4. Replace and Test

    Replace the outlet receptacle and screw all pieces back into place before turning the power back on. Test it to see if it works by plugging a light into the new GFCI outlet. Press the "Test" button to see if the outlet is working. It should turn the light off. Press the "Reset" button to see if it comes back on. If both of these work, then it is wired correctly.

FAQ
  • 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.

  • Can you wire a GFCI outlet wrong?

    An incorrectly wired GFCI won't protect against a ground fault. If the LINE wires are incorrectly connected to the LOAD terminals or vice versa, the GFCI will not provide power to that outlet.

  • What is the difference between line and load on a GFCI?

    A line wire carries the incoming power from the breaker box, while a load wire takes the power downstream to the next outlet.

  • Does a GFCI trip if the hot wire is grounded?

    If there is a ground fault for any reason, the GFCI should trip and shut the hot wire off.