What is a GFCI Outlet? Full Guide

It’s a good idea to know what a GFCI outlet is and how they work. Every home is supposed to have them. Patented in 1965, the GFCI outlet protects people from potential fatal electrical scenarios.

What is a GFCI Outlet? GFCI stands for “Ground-Fault Circuit Interrupter”, and it can literally save your life.

If your home or residence was built in 1971 or after, it should have GFCI outlets. Even if your place was built pre-1971, there’s a high chance some of the outlets were upgraded to GFCIs at some point.

Let’s examine how and why GFCI outlets are so important, where you can expect them to be, and how to test them.

What is a GFCI Outlet?

As its name suggests, a GFCI outlet (Ground Fault Circuit Interrupter), has the ability to interrupt or cut off electricity in the event of an electrical problem. It is a safety device intended to protect you from harm.

An uninstalled GFI outlet with the face plate laying beside it.

GFCIs are very sensitive to certain problems (sometimes, annoyingly too sensitive) and will quickly shut down current flow before you get hurt. Because this technology is so effective and reliable – it has become mandatory in many areas of your home. More on that later.

The GFCI outlet is designed to fit in a standard electrical box. That is – the length and width and mounting yoke are compatible so that you can usually swap out a standard outlet for a GFI.

However, the GFCI is about twice as deep. So there can be problems if the box is too shallow and/or has more wires. In this case, it’s necessary to change out the box as well.


What is the difference between the term GFI vs. GFCI?

Depending on who you talk with, you may hear the term GFI or GFCI. It’s common to hear what is a GFI outlet? Or, what is a GFCI outlet?


GFI and GFCI denote the same thing. GFI is just shorthand for GFCI. Therefore, you may encounter both terms in this article.

What is a Ground Fault?

So what is a “ground fault” and why do I care about it?

As you probably know – electrical current will always try to flow to ground.

Yes, I mean the actual ground under your feet.

The reasons for this are interesting but are better left for another time. Suffice it to say, if a generated electrical current can find a way to ground it will always take it. And will always take the path of least resistance.

If that path happens to be through your body – so be it. See the problem?

The scenario I just described is called a “ground fault”.

It’s when electricity is free-flowing to ground instead of where it is supposed to flow – in its’ circuit.

The circuit I speak of is on wires – from and then back – to its source.

Whenever current flows on the wrong path it’s like a train off its rails and bad things can happen.

So wouldn’t it be great if there was a device that could detect this problem and shut things down?

In 1965, an electrical engineer named Charles Dalziel figured out how to do it, and he invented a device called a GFCI.

The GFCI is a device that simply measures electricity flowing in a circuit. It makes sure that the amount of current entering a circuit is equal to the amount leaving. If not, it interrupts – shuts down – the power.

Just like if you send your three children off in a car for a day at the lake. You would expect three kids to come back – right? If less than three returns that would be a problem.

Similarly, if 1 amp of current speeds from the breaker panel to power a light bulb, then 1 amp of current should come back on the neutral wire (that’s the white one).

So, the GFCI measures the current flowing to and from a load.

If there is the slightest difference between the two, the GFCI outlet will shut down or “trip”.

Let’s imagine you are blow-drying your hair.

With a metal hair dryer.

While barefoot.

Standing in a puddle of water.

On a concrete floor.

The perfect storm!

Now, imagine a damaged wire in the hairdryer and the handle becomes energized to 120 volts potential – while firmly grasped in your hand.

Now current can, and does, begin to flow – not through the heater coil and motor where it belongs, but through you to ground; thus electrocuting you.

Not good.

People die very quickly from things like this.

But wait! Your hair dryer is plugged into a GFCI outlet. which is faithfully comparing current going to and from the dryer.

The GFCI, seeing the imbalance, trips; and trips very fast.

So fast, in fact, that the outlet shuts off before you get hurt.

This is the GFCI in a nutshell, if somewhat oversimplified.

It is very effective technology and has saved many lives through the decades.

GFCI and Electrical Shock- By the Numbers

For all you data types, here are some numbers.

First, let’s look at the effects of current flow on the human body. It doesn’t take much. In fact – we measure harmful amounts of current, not in amps- but in milliamps.

That is thousands of amps, or one amp divided into a thousand equal parts.

Talking about shock is an important part of the equation when talking about what is a GFCI outlet.

Degrees of Electrical Shock

Most of us have experienced a mild tingle sensation from accidental contact with a live wire. It’s mostly startling and scary, but not really dangerous. In this scenario, you have absorbed roughly 1-8 milliamps.

If you sustained more – let’s say, 8-15 milliamps, the result was a more painful shock. I’ve been there many times!

At 16-19 milliamps, we could be talking about muscle paralysis and the inability to “let go”.

This quickly leads to:

20-50 milliamps – Possible damage to nerve tissue and blood vessels 

50-100 milliamps – ventricular fibrillation and death.


When Does the GFCI Get Involved?

A typical GFCI device will trip when it detects an imbalance of around 6 milliamps.

This means that about the instant you perceive a slight tingle – everything shuts down before any real harm comes to you.

This is why it is such an important device and is required by code in many places around your house. Keep reading for the list.

Do Breakers Protect You From Electrical Shock?

Each electrical circuit is protected by a breaker – or fuse. All current must pass through this device before even leaving the electrical panel.

What do the breakers do? They limit the amount of current allowed to flow. Like a GFI, breakers, and fuses also have trip ratings. However, these are measured not in milliamps but full amps.

See the “15” stamped on the handle of that breaker? That means it will trip when and if it ever experiences an excess of 15 amps. That could occur from a dead short or if too much current is flowing at once.

For example, imagine you use a hair dryer, space heater, and microwave all at once on the same circuit. This may well exceed the breaker’s rating and trip it off. This isn’t a ground fault, but an over-current situation. So, not the same thing but bear with me.

OK – so the breaker trips off at 15-amps. Think your body could withstand that much current?

Since ventricular fibrillation and death occur at 50-100 milliamps (or .05 amps), I would say a 15-amp breaker might not save you. It would be like rappelling down a 100′ cliff with a 110′ rope.

Breakers are sized to protect the wires in a circuit from overheating – not to protect you. 

Legend holds that the inventor of this technology did something rather dramatic when demonstrating this to potential investors.

According to the story- he had his daughter sit in a bathtub full of water. And then, with everyone watching, plugged a hairdryer into a GFI outlet.

He then proceeded to drop it into the tub!

He really believed in his product! Or that wasn’t his favorite daughter.

Anyway – it worked!

The device tripped.

She was unharmed.

And the rest is history. No word on whether he was charged with reckless endangerment. 

So what do you think? Did this really happen?

Types of GFCI Devices

GFCI devices have proven themselves time and again as the best personal protective device – particularly in the home where most electrical accidents occur.

What types of GFCI devices are out on the market?

  1. Standard GFCI Outlet Receptacles
  2. GFCI Weather-Rated Outlet Receptacles
  3. Dead-Front GFCI
  4. Plug-end GFCI
  5. Outlet Adapter GFCI
  6. Integrated GFCI
  7. GFCI Circuit Breakers

Now let’s get into a bit more detail about each type of GFCI listed above.

Standard GFCI Outlet Receptacle

Outlet receptacles are the most commonly used type of GFCI. It’s simply a duplex outlet with two small buttons in the middle:

  • Test button
  • Reset button

Pushing the test button will shut off the outlet and exists to, well… test the thing. It simulates a ground fault and should pop. GFCI outlets can wear out and should be tested periodically.

The reset button turns the outlet on. Use this if the GFCI outlet has tripped off for any reason.

GFCI Outlet with the Reset Button and Test Button labeled

This plug can be used in at least two ways.

  1. It can be hooked up to protect just itself.
  2. It can be configured to also protect every outlet downstream in the circuit.
    For example – say you have 5 outlets on your kitchen counter, all on the same circuit. You only need one GFI installed at the first location. and all of the other outlets on that circuit will be protected as well.

    That will save you some cash – but it needs to be wired very specifically to work properly. (see image below)
  3. GFCI outlets can be configured with standard outlets upstream and downstream. When we talk about the “upstream” or “downstream” portion of a circuit it just means this:

    Power in a circuit has an origin point. All circuits begin at your breaker panel. If there are ten outlets in that circuit – and your GFI outlet is the 4th device from the panel – then outlets 1, 2, and three are upstream of the GFI, and outlets 5-10 are downstream. (see 2nd image below)

GFCI Weather-Rated Outlet Receptacle

A weather-rated (WR) is a variation of a GFCI outlet receptacle we just described. It’s the same thing except it’s rated for outdoor purposes. It still needs to be installed in a raintight box and cover – but it’s indicated to perform better in damp air. 

Dead Front GFI

A dead front GFI is sometimes called a dead face. It’s everything described above, but it’s not an outlet. You can’t plug anything into it. It’s just a reset button on a blank face. Otherwise, the GFI wires up the same way. 

What’s the point of that?

Many times we need GFI protection for something which does not plug in. Some things are hard-wired but still require GFI protection – like many dishwashers.

In that case, we run the dishwasher circuit through an outlet box first (often installed under the sink) and then install a dead front GFCI there, which then feeds the dishwasher.

Plug End GFCI

Some devices come with their own GFCIs included.

Look at the plug on a hairdryer. Chances are you’ll see a yellow or white button near the end. That’s a GFCI.

You can also buy extension cords or multi-plug splitters which incorporate GFI technology. They will always sport that test/reset button. So this can be used anywhere and will be protected.

Outlet Adapter GFCI

This product needs no wiring, tools, or knowledge at all. It’s a GFCI outlet on the front and a three-prong plug on the back. Just plug it into any outlet and you’re done.

Integrated GFCI

Similar to the plug end from above. Some items are designed with GFI protection built into the product itself. A good example is a floor heat control module. It has an internal protection circuitry but sports the tell-tale reset button on its face.

Another example is the spa disconnect. This is a small breaker panel with a 240-volt, GFCI breaker included. When used to power up your hot tub it protects the pump motor and everything else involved.

GFCI Circuit Breakers

A GFCI Circuit Breaker installs in your electrical service panel and gives GFCI protection to everything on the circuit.

Like a GFCI outlet, this kind of breaker has a test button as well.

Should I Install a GFCI Circuit Breaker?

  • GFCI circuit breakers do have some unique install requirements so you’ll need to do some research or hire an electrician for help.
  • It’s expensive but sometimes worth it depending on your situation.
  • We use them for equipment circuits that require GFI protection but are hardwired. Swimming pool pumps are a good example. 
  • In my experience, GFI circuit breakers tend to end up in older homes where Installing GFI outlets is too much trouble.

GFCI Breaker vs. Arc fault Breaker

In case you aren’t confused yet here’s another thing.

Some States require arc fault breakers in homes for general circuits in living areas. We call them AFCI. They look exactly like a GFI breaker – and even hook up the same way – but the arc fault breaker is different, so read the package carefully.

Arc fault technology is used to detect, not a ground fault – but, you guessed it, an arc. If you’ve ever unplugged your vacuum cleaner while it was running, you likely noticed a decent spark.

That’s an arc. Albeit a harmless one.

Other arcs are cause for concern. So the arc fault breaker protects against that scenario.

Why did my GFI Trip and What Should I Do Now?

Do you have a tripped GFCI? There are three basic reasons a GFCI outlet will trip.

  1. The dreaded nuisance trip. The benefits of GFCIs are also their downside. They’re very sensitive. Sometimes they just trip. Could be humidity, slight fluctuation in the incoming voltage, or just because it’s Tuesday. If that’s the case, simply push the reset button to clear the fault and you’re back in business. I always begin with easy – resetting the device. But if it won’t reset it could be:
  2. An actual ground fault. If this is the case then your GFI is doing its job. The trouble could be anywhere in that circuit. It could be a wiring problem in a wall or outlet box that you can’t see.

    Be aware, however, that the problem can be with anything plugged into the GFI – or outlets protected by the GFI. So, the first thing you should do is unplug anything in that circuit: lamps, appliances, radio – whatever. If the problem is one of those you will eventually narrow it down.
  3. A Damaged GFCI. These things don’t last forever and because they’re so sensitive, GFCIs can have short lives. Voltage spikes and lightning strikes can be lethal to GFCIs. If you are comfortable doing so, you can replace the device and see if that helps.

If none of the above resolves the problem, you may well want to call an electrician to help out.

How Do I Test My GFCI Outlet?

Testing your GFCI outlet is super easy. You should actually test your GFCI outlets at least once a month. 

That is, checking every receptacle, portable device, or circuit breaker. If any GFCI device fails to either trip or reset, that usually means you need to replace it.

Upclose up test and reset buttons on a GFCI outlet

To test your GFCI outlet:

  1. Press the test button. If it’s a receptacle, the reset button should “pop” . If a breaker – you should see the handle turn off.
  2. Verify that power is cut off after pressing the test button.
  3. Press the reset button once you confirm the GFCI outlet is doing its job. This should restore power. If a breaker, flip it to the full-off position, then back on.

You should also test your GFCI outlets after a strong thunderstorm since lightning may interfere with your home’s power sources.

What is a GFCI Tester?

A GFCI tester is a product I think every homeowner should have. You’re probably familiar with a standard plug tester – that’s the device you can plug into a wall outlet to see if it’s on. The lights on the tester light up – or don’t – telling you the condition of that outlet.

a hand putting a gfci tester into a gfci outlet

The GFI tester is a similar tool with a little black button in the middle. If any random outlet in your house is GFI-protected you can easily prove it.

How to Use a GFCI Tester

To determine if a standard outlet is GFI protected, plug a GFCI tester into an outlet and push the black button. That secret button, when depressed, will trip the GFI on the circuit, wherever it is in the house. It could be in the basement, or it could be upstairs in the bathroom. If there is a GFI governing that outlet – it will shut off.

Of course, now you have to go find the tripped GFI – which can be another adventure!

So with a GFCI tester, we can prove two things:

  1.  Whether or not a standard outlet is GFI protected.
  2. Whether or not the GFI itself is working properly.

A GFCI tester is a nice device to have and is relatively inexpensive.

Where Should GFCIs Be Installed?

What things should be GFI protected in my house?

The National Electric Code (NEC), for those in the U.S., is quite specific and extensive about what must be GFI protected in a residence.

The list is somewhat long and ever-growing as the code changes every three years. What began as a really good idea has become required.

As you consider the list below keep in mind that GFI protection can be achieved by any of the methods shown earlier in this article.

Where are GFCIs Required Inside?

You want to stay safe inside your home. Many GFCIs are required inside – perhaps in more locations than you realize.

Generally speaking, the items listed below will fall into at least one of two categories: 

  1. Outlet Receptacles or
  2. Equipment

With a few exceptions, lighting fixtures are not GFCI-protected.

You will see that most things that need GFCI protection are near or involved withWATER. Any outlets or equipment which may get wet or are within four feet of a water source must be GFI-protected.

Here is the list of the GFCI locations required inside your house:

  1.  Kitchen counters, islands, and, really any outlets in your kitchen. Even if it’s more than 4 feet from the sink, all Kitchen counter outlets must be GFI protected. Remember, one GFI can protect multiple outlets.
  2. Range receptacles – if it’s within 6 feet of your kitchen sink it needs to be GFI protected. That would be a breaker-style GFCI.
  3. Microwave This one depends. If it’s the kind that hangs over your stove, a regular single receptacle is allowed. If it’s on the counter, then a GFCI is necessary.
  4. Refrigerator – YUP, sorry. That’s because of the water line connected to it for ice.
  5. Sink Disposer
  6. Dishwasher
  7. Bathroom counter outlet
  8. Jacuzzi Tub
  9. Washing machine
  10. Sump Pump
  11. Heated floors ( these usually have a GFIC built into the control device.)
  12. Basements – until recently, only receptacles in an unfinished basement needed GFCI protection ( “unfinished” meaning concrete floors). But the latest code update removes the distinction between finished and unfinished. Now every outlet in a basement must be GFCI-protected.
  13. Laundry – all outlets in the laundry room including your electric dryer. ( if it is a 30-amp, 240-volt electric dryer – you would need a breaker-style GFCI.
  14. Lights Generally, permanently installed lights are not GFI-protected because they are usually out of reach. One possible exception is a light in the shower. But that can be avoided by using a recessed fixture with a vapor-proof lens – which is about the only thing people use anyway. 

Where are GFCIs Required Outside?

Now let’s go outside to your exterior outlets. Where are GFCIs required outside?

  1.  Any exterior outlet on the house. They must also be weather-rated (WR) with an appropriate weatherproof cover.
  2. Outlets in landscape areas
  3. Pumps: Pools, Pond Irrigation, etc.
  4. Hot Tubs or spas
  5. Garage? Yup!
  6. Garage door opener

For pretty much anything outside – plan on GFI protection.


Our full guide to GFCIs has fully answered the question: What is a GFCI outlet? The benefits of installing GFCI outlets include a reduced risk of being electrocuted and the prevention of electrical fires. While national codes require homes built since 1971 to have GFCI outlets, you may want additional protection.

You can further protect yourself and your home by installing GFCI circuit breakers, cord-connected devices, and portables. Always hire a licensed electrician or contractor if you’re unsure how to swap these out yourself.