How GFCI Outlets Work & Why You Need Them

GFCI outlet

Electricity has become an enormous part of our lives, so big that it is almost impossible to live without it. Ground fault circuit interrupters (GFCI) entered the electric code in 1973, and their use has grown since. GFCI protective devices prevent electric shock due to ground faults. Let’s discuss how GFCI works.

Ground Fault Circuit Interrupter (GFCI) outlet is a safety device that protects against electrical shocks in wet areas. A GFCI outlet uses a built-in sensor that monitors electricity between the hot and neutral inlets. When a ground fault as low as 4 or 5 milliamps is detected, the sensor trips to cut the electrical power to the circuit.

In other words, a GFCI outlet works by cutting electric power to an electrical outlet to protect against electrical shock. GFCI electrical outlets have a sensor that detects electrical imbalances as low as 4 to 5 milliamps across the hot and neutral wires. When an imbalance occurs, the sensor instantly breaks the circuit rendering the circuit dead. Power can be restored by resetting the tripped outlet or breaker.

The accidents have dramatically decreased since the introduction and the consequent increase in GFCI outlets usage.

They provide high levels of protection and safety for us and our homes. That is why it is essential to be adequately informed and better understand how they work, recognize them, and expect them.

How Does a GFCI Outlet Work?

A GFCI outlet improves the overall safety of your home. Not everybody is a qualified electrician, and all the technical vocabulary can be confusing. Don’t worry. You don’t need to know every term to understand and learn crucial details.

The GFCI outlet works to detect variance with the electricity as it travels through the outlet. When a problem is detected, it shuts itself off, stopping any electrical current from that particular outlet to protect against electrical shock—the below graphic diagrams how a GFCI is wired to protect an entire circuit.

The GFCI Outlet

Take a look at your outlet. Here in the United States, we have two vertical slots, usually on top and another round hole below them.

  • The left slot is the “neutral,“ and the right is the “hot.“ The round one beneath them is called the “ground.”
  • When you plug in an electrical appliance, the electricity will flow from the hot wire to the neutral wire. If the neutral wire is loose, the open neutral will cause the GFCI to fail.

The GFCI has a sensor that tracks the flow of electricity. The current flow usually remains the same (with some slight losses). However, if a ground fault happens, this will create an imbalance. That imbalance will be registered instantly by the GFCI, and it cuts off the power in the outlet and any outlets downstream from the circuit.

The GFCI outlets work fast, which is vital to saving lives. It can detect as small imbalances as low as 4-5 milliamperes, and it can trip the circuit in one-thirteenth of a second. You might feel a slight pinch in that short amount of time, but the GFCI will stop any prolonged exposure to the life-threatening electrical shock that might be lethal.

Just for comparison, at ten milliamperes, human muscles paralyze due to the electricity passing through the body, and only two seconds of this are enough to cause death.

The regular outlets cannot monitor the current and provide such protection. However, they can be used on a GFCI protected circuit, provided the GFCI is on the leading outlet.

For example, you will often see bathrooms with a standard outlet in new construction homes but have GFCI protection from another bathroom outlet. Another example is where exterior outlets will be GFCI protected through a GFCI outlet located inside a garage.

It is common for you to find a GFCI outlet positioned closest to the electrical panel box, and the GFCI will protect other areas through the same circuit.

GFI vs. GFCI: Are They Different?

There is no difference between GFI and GFCI, and the terms are interchangeable. Ground Fault Interrupter (GFI) and Ground Fault Circuit Interrupter (GFCI) both detect ground faults and will “interrupt” the flow of electricity to the circuit when ground faults occur.

Use of the term GFCI is more common than GFI among manufacturers and electrical contractors but there is no difference in the device’s function.

What is a Ground Fault?

Many people understand how a GFCI outlet works but don’t truly understand a ground fault. 

A ground fault describes how electricity unintentionally exits a contained electrical path and follows its natural flow directly to the earth (ground). In our homes, electrical wiring uses insulated sheathing to contain electricity. As foreign objects contact an electrical circuit, electricity will attempt to follow this unintended path to the ground.

The electricity is traveling through the wires in your home. These wires contain electricity because they are covered in plastic insulating material. The electrical current travels safely through the wires, reaching any electrical devices and equipment plugged in if everything is working correctly.

That is not necessarily what is natural to the electrical current, though. Electricity is always looking for a place to ground itself. That’s why lightning usually strikes the earth (negative to positive).

When a ground fault happens, the electrical current has escaped the wiring and its intended path and goes into the ground. Ground faults can occur due to bad wiring or installation, damaged wires, and when the current is in contact with an appropriate conductor.

Water is one such conductor. There is a high risk of a ground fault when in contact with water. Therefore, the National Electric Code (NEC) implemented ground fault protection in wet areas, like bathrooms or kitchens.

Why are Ground Faults Dangerous?

During the ground fault, the electricity has taken an unintended path. In doing so, it will use any conductor to pass through it and reach the ground. If that conductor is a human being, this can lead to electrical shock and electrocution, which happens just once.

Our muscles will “freeze” due to the electrical current passing through our body when that happens. For example, if you grab a damaged wire and you get electrocuted, you won’t be able to release it, thus maintaining the connection between you and the electrical current.

Just a few seconds of this are enough to cause death. That muscle paralysis is so dangerous as you might not let go of the wire leading to a fatal result. If another person touches you in the meantime, they can feel the electrical shock, putting them in danger, too.

What Causes a Ground Fault?

The biggest reason for ground faults is moisture (or dampness) and environmental conditions. Since water and electricity are a deadly combination, it’s essential that GFCI is present and routinely tested.

A ground fault can also happen when the wiring insulation is damaged or due to faulty wiring. When inspecting a home, there is a reason why pest inspection is essential as rodents can chew through the wiring, causing a lot of unexpected costs and health hazards.

Where Should You Install GFCI Outlets?

GFCIs can be considered an electrical safety feature that you need to make sure you have installed to protect your home and family. GFCI outlets don’t need any special care. You should test your GFCIs monthly by pressing the test button to check if they are still functioning correctly.

Testing is critical with outside GFCI outlets because they wear out faster than GFCI outlets installed indoors. GFCIs have been introduced into the electrical code and are required as follows.

You should install GFCI outlets in places and rooms where appliances are frequently used close to water sources. Any water or moisture can increase the chances of receiving accidental shocks.

If you are buying or moving into an older home, you need to know that older homes are not required to have GFCI outlets unless you will update the wiring, in which case the receptacles need to be changed. This means that older buildings might not have any GFCI protection, and while working with appliances outside or close to water, you should take extra care.

According to the NEC (National Electrical Code) standards and recommendations, a GFCI should be installed in places such as, but not limited to:

YearNEC GFCI Code Additions and Revisions
1971Receptacles within 15 feet of pool walls
1971All portable swimming pool equipment
1973All outdoor receptacles
1974Construction sites
1975Bathroom receptacles, 120-volt pool lights, fountain equipment, and boathouses
1978Garages, spas, and hydromassage tubs
1978Exception for GFCI receptacles located above ground
1981Exception for garage receptacles for dedicated equipment or not readily accessible (garage door openers power supply that can not be reached without a ladder)
1984Replacement of non-grounding receptacles with no grounding conductor allowed
1984Pool cover motors
1984Distance of GFCI protection extended to 20 feet from pool walls
1987Unfinished basements
1987Kitchen countertop receptacles within 6 feet of a sink
1987Boathouses
1990Crawlspaces (with an exception for sump pumps or other dedicated equipment)
1993Wet bar countertops within 6 feet of a sink
1993Any receptacle replaced in an area presently requiring GFCI
1996All receptacles on kitchen counters (6 feet rule expanded)
1996All outdoor receptacles except dedicated de-icing/cable receptacle
1996Unfinished accessory buildings at or below grade
1999Exemption for dedicated equipment in crawlspace removed
2003“Smart Lock” type GFCI receptacles required
2008All receptacles in the garage (exceptions removed)
2014Expanded to include dishwasher, laundry rooms, wall outlets within 6 feet of the outside edge of a bathtub or shower stall

This is because water can conduct electricity, and there is a high risk of creating a ground fault and receiving a shock.

During the past several decades, with every code revision done, the areas required to have GFCI equipped receptacles have been expanding. The revisions are usually done every three years. As you can see, very few places and rooms are not required.

It is not required to install a GFCI outlet in any bedrooms, living rooms, or other rooms with no running water or plumbing fixtures. It is still considered okay to use a regular outlet in those areas.

Difference Between a GFCI Outlets & Breakers?

So far, it sounds as if they are the same thing. So you might wonder whether or not you need GFCI outlets or breakers.

Both serve different purposes and protect the home and you in different ways.

  • The GFCI circuit breakers’ primary purpose is to cut off any electricity flowing through the wires in a particular circuit. When a sudden surge in the current flows through the home’s electrical system that surpasses the wires amperage, the circuit breakers will trip, protecting the home from any electrical fires.
  • The GFCI will offer protection in a different aspect as it will stop the electricity flowing through the outlet where there are signs of ground faults or short circuits. In addition to that, this happens almost instantly. You can protect most of the GFCI required areas at the outlet location. However, GFCI breakers work well for safeguarding outlets in areas not readily accessible, like jet tub motors and crawl spaces, or for protecting 3-prong outlets by replacing ungrounded outlets where the whole house needs protecting.

How to Know if My Outlet has a GFCI?

Since proper GFCI outlets and breakers provide safety, anyone should recognize them.

The easiest way to identify receptacles with GFCI protection is to look for the two buttons they usually have. Often they will come with a “Test” and a “Reset” button.

That is so you can test if the GFCI is working correctly. Some outlets even have an indicator light on them. Usually, an outlet containing a GFCI should also have a label, but that is not always the case.

In some cases, a few different outlets can be connected to a single GFCI, so there might be no visible clues on the outlet themselves. A GFCI protection can be provided by a distribution panel equipped with a GFCI breaker, and it can protect several different outlets connected to it.

Because of that, it is essential to know that just by taking a quick look at an outlet, it might not always be possible to tell if there is GFCI protected or not.

How to Know if Your GFCI Receptacle is Working?

Since we are talking about home and personal safety here, it is vital to understand how a GFI outlet works and determine if it has failed. If your GFCI has a blinking red light, it has likely failed.

An outlet like this doesn’t require any special maintenance (just like a regular outlet), but it certainly has some life expectancy. A GFCI outlet should be tested every month and replaced every ten years. A GFCI outlet can last 15 years or more.

Like anything, GFCIs can break, wear out, or become faulty over the years if you live in an area with high lightning activity. The time until a replacement can go down to even five years or less.

To check if the outlet is working correctly, you can test it. The test takes just a few seconds, and it doesn’t require any additional equipment. You don’t have to power off the whole electrical power.

outlet tester

How to Test a GFCI Outlet:

You can quickly test a GFCI outlet or circuit. Here are the simple steps.

  • Take a look at the outlet – between the top and bottom receptacles, there should be two small rectangular buttons. It should say Test, and on the other, Reset.
  • Press the Test button. Then the outlet should create a click sound as it shuts off the power to the plug connectors.
  • Make sure there is no power in the connectors by plugging in a table lamp. The lamp should not turn on.
  • When you are sure there is no power, press the Reset button to ensure the outlet is back to working usually. If you plug in the lamp now, it should be working.

Keep in mind that the older GFCI equipped outlets can fail while being closed, and despite being tripped, they will still conduct electricity. This means that there is zero protection against any electrical faults.

On the other hand, newer models usually fail while being open. Although they will not work anymore, they still have cut off the electrical current.

Another point of concern is if the outlets are wired correctly. If they are wired backward (also called reversed polarity), a newer unit will not work, while an older receptacle will not offer GFCI protection.

I recommend the FLIR RT50 Receptacle Tester available on Amazon. The FLIR Receptacle Tester has a built-in GFCI test button to allow you to test GFCI protection on outlets downstream from the lead GFCI outlet.

What are the Different Types of GFCIs?

A GFCI can be installed and found in various locations, and sometimes it might look a bit different. This doesn’t change anything, as the way the protection works is virtually always the same.

Here we will go through the three most common ways a GFCI is being installed:

  1. GFCI Equipped Outlet

As we have just discussed, the standard GFCI outlet has protection built inside it. This outlet only offers shock protection to the connected appliances and is the most commonly used and cheap method.

Also, some appliances come with in-built GFCIs, so they might not necessarily need extra protection, but most of them still don’t have proper GFCI protection.

  1. GFCI Circuit Breaker

The GFCI circuit breaker, on the other hand, has several different outlets connected to it, and it protects all the receptacles connected to it. If the GFCI detects a ground fault, the breaker trips inside the main service panel box, killing power to the entire circuit.

Usually, you will install the GFCI in the panel at the circuit breaker. The way to recognize it is to have a yellow or red Test button near the electrical panel switch. Failure of the GFCI breaker or outlet is a common electrical defect. If your breaker box is old, you may need an electrical panel replacement.

  1. GFCI Dead Front

The GFCI dead front is another variation that you might see. A dead front usually has just two buttons on it and provides an easy way for anyone to test it and reset it if it trips. GFCI has “Test” and “Reset” buttons only with no receptacle outlets.

It is usually used to protect remote appliances that are not easily accessible – like the bathroom’s spa pump, which is often built inside the walls near the electrical panels or a bathroom.

Do Home Inspectors Check GFCI Outlets?

If you are in the process of buying a new home and you are worried about the state and condition of the receptacles (outlets), a home inspector will help you.

The home inspection checks the overall condition of the home. Home inspectors examine readily accessible and visible systems, including testing electrical receptacles.

Older homes still might not have GFCI protection on some or all outlets. A home inspector or professional electrician can inform you about any electrical safety issues, including a lack of GFCI protection.

If the home you are interested in doesn’t have GFCI protection, a licensed electrician can often correct this.

Photo of author

Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.
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