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How to Install a GFCI Outlet

Dan has been a licensed journey-level electrician for 17 years. He has extensive experience in most areas of the electrical trade.

Wiring a GFCI Outlet

Wiring a GFCI Outlet

Reasons for Installing a GFCI Outlet

There can be several reasons you may want to install a GFCI outlet—maybe it's worn out, physically damaged, or maybe you just want a new one.

Like any other outlet, GFCI outlets will wear out eventually. Kitchen outlets often have small appliances repeatedly plugged into them and then removed after use. Has constant use worn out the springs that keep the plug tight?

Has something damaged the outlet? Grease from the range, striking one in the garage, or filling one outside with water too many times?

Or do you just want an additional outlet? Maybe one to power a new freezer in the garage?

Whatever the reason, there are a variety of things to consider before wiring in a new GFCI, and it will pay to take a look at them before starting the project.

Using a non-contact voltage detector, an indispensable safety tool when working with electricity.

Using a non-contact voltage detector, an indispensable safety tool when working with electricity.

Where Should GFCI Outlets Be Used?

The National Electric Code gives certain requirements for the placement of GFCI outlets, in that specific areas are required to have a GFCI outlet rather than a regular outlet. These include:

  • Non-livable areas such as a garage or attic.
  • Outdoor areas; the outlet near the door must be a GFCI.
  • Anyplace within 6 feet of a water source or sink. Kitchen countertops, bathrooms or near a hot tub for instance.
  • Service outlets near equipment. An outlet, for instance, near a furnace and intended for use by servicemen must be GFCI protected. These will usually, but not always, fall under one of the other categories as well.

It is often not a good idea to install a GFCI when the intended purpose is to operate a motor-driven appliance as motors will occasionally trip the ground fault protection. A freezer in a garage, for example, may trip the GFI but may not be found for days or until food has thawed and been destroyed. Another place might be under the kitchen sink; that is within 6 feet of the sink but a garbage disposal or dishwasher may cause nuisance tripping.

Some electrical inspectors or locations may allow exceptions, usually by requiring that a "simplex" outlet, one with just one place to plug into, is used. If you want an exception, you should check with your city building department.

What Type of GFCI Should I Buy?

While there is a range of colors available for GFCI outlets, the hue won't make any difference. Much more important is the ampacity of the outlet. These outlets are available in two different ampacities: 15 amp and 20 amp. In general, any outdoor, garage, or kitchen circuit is probably a 20 amp circuit, while older homes probably have a 15 amp circuit in the bathroom. Newer homes are now required to have a 20 amp circuit there as well.

The key is to match the ampacity of the outlet with that of the circuit. Locate the breaker or fuse feeding that circuit by turning them off until the circuit to be used goes dead, and note the figure on the fuse or breaker handle. The new GFCI outlet must be matched to that number; a 15 amp circuit must have a 15 amp outlet while a 20 amp circuit must have a 20 amp outlet.

GFCI outlets normally come with a cover plate, so an additional purchase of the proper cover plate isn't necessary. In the two possibilities shown below, notice the shape of the straight slots: the 20 amp outlet has a "T" shaped slot on one side.

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How to Wire a GFCI Outlet

Before beginning to wire your outlet, you will need to decide whether it is to protect any "downstream" outlets that may have been installed previously.

Any electrical circuit begins at the panel box, goes to the first device or outlet, and from there to others. Those that are electrically further away from the panel are termed "downstream" and can be protected from ground faults by any GFCI outlet that is "upstream" from them.

  1. The first step is to turn off the power and, if possible, test it with a voltmeter or a non-contact voltage detector.
  2. If you don't want to protect downstream outlets (maybe it's a freezer outlet) then all the wires in the box will need to be spliced together with a "pigtail" to the outlet. Splice all the black wires together, including a 6-inch piece (of the same wire size!), all the white wires the same way, and lastly all the bare, ground, wires. Use the 6" piece to terminate on the outlet.
  3. The outlet will actually have two sets of connection points, with the one for the "load", or downstream, wires and one for the "line" wires - those that are coming from the panel or upstream outlets. The load connections generally have a piece of tape over them from the factory but are also plainly marked on the back of the outlet.
  4. Insert the black wire into the hole near the brass-colored screw and tighten the screw. The white wire goes into the hole near the silver-colored screw and the ground wire goes to the green screw, usually at one end rather than the side of the outlet. The ground screw will often need to be bent into a loop to fit around the screw before tightening it.
  5. Remove the tape if you will have to load side wires to downstream outlets and repeat the process, this time with only black and white wires; there is only one spot to terminate the grounds.
  6. Fold excess wire into the electrical box as neatly as possible, push the outlet in and attach it to the box with the screws provided. Attach the cover plate, turn the power on and reset the outlet with the push button on the front. Test the outlet with a either GFCI outlet tester (preferable) or at least the push buttons on the front of the outlet - you're finished.
Back side, showing holes to insert wires into before tightening the screw on the side.

Back side, showing holes to insert wires into before tightening the screw on the side.

Connections for the neutral (white) wire and ground.  Load wires go behind the tape.

Connections for the neutral (white) wire and ground. Load wires go behind the tape.

Connections for the hot (black) wires

Connections for the hot (black) wires

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: When you say "load wire," do you mean going downstream to another outlet?

Answer: Yes. The "load" terminals on a GFCI outlet refer to the wires feeding a downstream outlet.

Question: How do I deal with an older home with two conductor/wire outlets for an outside wall plug servicing the patio?

Answer: You may add an outlet to two-wire systems, but it must always be a GFCI. As there is no ground you will not ground the new GFCI: there is a sticker in the package (or should be) that notifies future people that the outlet is ungrounded.

Question: Can installing a GFCI outlet be done with 4 sets of wires coming into the box?

Answer: Yes, although so many wires in one box can make it difficult to get the new outlet in as well. GFCI outlets are larger than normal ones, and the space is limited.

But if there is sufficient space, splice all the black wires together with a wire nut, including a 6" piece of additional wire. Do the same with the white wires and the ground wires. Use the new "pigtails" to terminate on the screws of the new GFCI outlet.

Question: How do I to change from old-style GFI's with pigtail ground wires to the new style?

Answer: Instead of splicing the ground wire to the pigtail, terminate it at the green ground screw.

Question: Do GFCI's work on a single phase line to ground supply?

Answer: A GFCI outlet works by comparing the current on the hotline with the current on the neutral. When they are not equal within a very narrow tolerance, it trips. No ground is necessary for a GFCI to operate, but they are designed for single phase only. A two pole GFCI breaker may be purchased, but it is still single phase current.

Question: Do you use the load side of the GFCI to supply a second GFCI?

Answer: No. The load side of the GFCI is used to protect a second, regular outlet. Never use the load side as the supply to a second GFCI - the protection is already there in the first one. Simply use a regular outlet as the second outlet, using the load side of the GFCI to supply it.

If you wish to use a second GFCI rather than a regular outlet, splice into the "line" side of the first to supply power to the second one.

© 2012 Dan Harmon


Dan Harmon (author) from Boise, Idaho on February 19, 2020:

Unfortunately, "line" and "load" is the terminology printed on the outlet. Without the instruction given here those terms would be meaningless. The article also plainly states where the black, white and ground wires go.

Paul on February 19, 2020:

Stop with the “load” “line” “hot” “neutral” lingo! How bout white, black, and ground.

Dan Harmon (author) from Boise, Idaho on June 16, 2019:

Using the buttons on the outlet, trip the gfci and reset it. If that doesn't fix the problem, replace the outlet.

Joe T on June 09, 2019:

My new Lutron 15 amp gfci has a green light but does not provide power to any appliance. I tried using one and both load lines but still no power, just green light. I also have a light switch connected downstream. Lightswitch works, outlet doesnt.


Dan Harmon (author) from Boise, Idaho on October 03, 2018:

That is correct. A GFI can protect multiple outlets, but it cannot be used to provide for multiple GFI's. They simply won't work.

It is possible that one of our GFI's is wired incorrectly in an effort to provide protection for other GFI's downstream, but that's unlikely unless it has been tripping since it was installed. Most likely one or more of them is simply going bad and needs replacement. Replace the one that is tripping, once you have verified that the load that is tripping it is not defective.

To test that, plug that load into a different GFI and see if IT trips as well - if it does, whatever you are plugging in is defective in some manner. I would add here than things with a motor in them (freezer, for instance) will often trip a GFI; it's why such normal outlets are sometimes used even where a GFI would otherwise be indicated.

Diane on October 03, 2018:

So you are saying that outlet 2 and 3 that are on the same circuit

as the GFI in the garage if I switch 2 and 3 back to regular outlets they

will not be protected by the one in the garage? If so, do I just replace

the one that is tripping or do I have another problem?

Dan Harmon (author) from Boise, Idaho on October 01, 2018:

@ Diane

You cannot wire outlets so that one GFCI protects another GFCI down the line. The second one won't work.

This means that the second and third outlets, that you wish to change from GFCI to regular, are NOT being protected by the first one and if you change them there will be no protection at all on them.

Diane on October 01, 2018:

Hi Dan

When I moved into my house 10 years ago I noticed that the bathroom

upstairs and the powder room downstairs had no GFI so I electrician

put them in. No issues except with plugging in night lights. Recently

the power went out and when it came back on it tripped the GFI upstairs. Now after turning off that breaker I realize that there are 3

on the same circuit, the garage-powder room and the upstairs bathroom. Can I just change the two back to outlets since I believe

they are protected by the one in the garage?

Dan Harmon (author) from Boise, Idaho on May 15, 2018:

@Mike: Instructions are given in the article on how to add additional outlets either protected or not. Briefly, splice into the wires feeding the GFCI if you do NOT want protection downstream, use the "load" terminals if you DO want the others protected.

Mike L Schneider on May 15, 2018:

Question Dan. If I follow these GFCI outlet instructions. Only the GFCI outlet will be protected. Nothing down stream correct ? I'm looking to add a junction box off it in the attic crawl space so I can add a light and possible more outlets that do not need protection. Would this work following these instructions ? Thanks

Marcy Goodfleisch from Planet Earth on February 18, 2013:

I need to learn some basics at home - I know so many women who understand how to do these things, and I am totally not able to do them!

Thanks for the lesson here! Voted up and up!

Dan Harmon (author) from Boise, Idaho on December 27, 2012:

Have fun, Wesman - I hate putting outlets into stone work. Few masons will provide a smooth surface for the cover plate so it usually ends up looking awful.

Then, too, digging ditches in 25 degree weather, maybe while snowing, isn't my idea of fun either!

Wesman Todd Shaw from Kaufman, Texas on December 27, 2012:

I'll be putting some of those in today. A fairly wealthy guy had his back porch extended, and an outdoor kitchen put in....nice stone work surrounded the electrical boxes...and the sinks are mounted on top.

Sadly, it is 25 degrees here in Texas...and I'm going to have to do some digging to get my underground pipe/wire ran over to the garage/breaker panel. :)

Dan Harmon (author) from Boise, Idaho on December 26, 2012:

Thanks, Jellygator. Yes, it could be valuable information to a new homeowner.

jellygator from USA on December 26, 2012:

Added this to my real estate website.

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