How Do GFCI Outlets Work?

gfci outlets

GFCI outlets (Ground Fault Circuit Interrupter) are devices that protect people against electrical shocks. They shut off an electrical power circuit upon detecting an imbalance of current between the wires of the circuit or when the electricity flows along an unintended route, such as through water or a person.

The Importance of GFCI Outlets

What is the amount of electricity that can kill an adult person? Only 20 milliamps. Do you know the voltage at which a circuit breaker trips? Thousand times more than what can kill you! GFCI outlets are a lifesaver as they shut down a power circuit at a 5 milliamp short to ground. The prompt response saves lives and dramatically improves the electrical safety at your home.

We know that the combination of electricity and water is recipe for disaster. For this reason, you have to be extra careful and tricky with the installation and placements of electrical outlets in places where water is used such as bathrooms and kitchens.

GFCIs are the best outlets for places where water is nearby. They reduce the risks of shocks, electrocutions, and burns along with preventing electrical fires. These have a built-in circuit breaker that interrupts the course of electricity in the event of an imbalance.

The building codes in the United States and North America require the installation of GFCI outlets and circuit breakers s in every structure.

What Are the Types of GFCIs?

leviton gfci outlets
Leviton Decora® SmartlockPro® 2-Pole Tamper-resistant self-test GFCI receptacle

GFCIs work like a kind of fuse or circuit breaker but their functions are different. The last two devices blow or trip in case of an electrical surge. They protect the wiring system from the fire but the protection does not extend to safety from electrocution. This is where GFCI outlets are unique.
There are three types of GFCIs. They are:

Receptacle GFCI – Similar to a regular wall outlet, these are the GFCIs that most consumers are familiar with. They offer two different levels of security, depending on the wiring. Single-location wiring provides GFCI protection to a single receptacle whereas multiple-location wiring guards one GFCI and every other receptacle downstream of it in the same circuit. However, the protective feature does not extend to the circuit between the main service panel and a multi-location GFCI.

Circuit Breaker GFCI – Having the capacity to safeguard all the receptacles on a particular circuit, it can replace a standard breaker in an electrical circuit. Just install it in the main service panel and it will protect all the wiring, receptacles, and devices connected to that circuit.

Portable GFCI – It provides temporary protection to electronic devices and tools in construction sites and outdoor settings. It cannot be an alternative to regular GFCI outlets and needs testing before every use for safety purpose.

How Does GFCI Outlets Work?

Knowing the functions of fuses will help you understand the mechanism of GFCIs more easily. A fuse is a device that protects a place from fire hazards by disconnecting a circuit in the event of electrical surges. The electricity spike is the consequence of the hot wire touching the neutral wire for some accidental reasons such as driving a nail through the wire inside the wall or a mouse chewing through the insulation.

When this happens, a dangerous amount of current will flow through the circuit, overheating it pretty quickly and starting a fire. Fortunately, a fuse heats up faster than the wire and burns up before the fire can start. A circuit breaker also does the same thing but it trips instead of burning itself during an overheated condition.

A GFCI does almost the same thing but in a subtler way. The standard 120-volt outlets used in the U.S. have two vertical slots with a round hole in between them. The slightly bigger left slot is called ‘neutral’, the right slot is ‘hot’, and the round hole is ‘ground’. A GFCI outlet monitors the current flow from hot to neutral and trips the circuit upon detecting any imbalance.

Only a 20-milliamp of electricity is enough to kill a person but a breaker or a fuse reacts to current 1,000 times more than this. If the current returning to the power supply is not equal to the current leaving the source, a GFCI spots that imbalance. It can sense a difference of as little as 5 milliamps and react pretty fast, one-thirtieth of a second, to open the switching contacts and de-energize the circuit.

The quick reaction time of GFCI outlets makes them a great device for ensuring electrical safety for human beings. They provide special protection in places where a slight current overflow could be dangerous. Think about standing with a power drill on a damp ground or using a hair dryer in a water-drenched bathroom. Given that the appliance you hold is wet, you could be electrocuted if electricity accidentally travels from hot to ground instead of the neutral wire. However, a GFCI prevents that by cutting off the power supply whenever it senses a disproportion.

At this point, it makes sense to mention AFCI outlets that provide protection almost similar to the GFCIs but against a separate potential danger. They safeguard against electrical arcs that can create bigger hazards like starting a fire.

Electrical arcs are the after-effect of piercing something sharp (like a nail) into the wiring or having it chewed or frayed by rodents. Some household appliances that transform electricity into heat like a toaster or a clothing iron also create arcs by sending some heat to the point where they plug into the wall. You can see the arcing by quickly unplugging the device from the socket.

What Are the Reasons for GFCI Outlets Failure?

GFCIs provide protection in dangerous life-threatening conditions but they don’t give you the license to be careless. It’s not uncommon for these outlets to fail. Also, you can experience serious electric shocks by touching a circuit’s hot and neutral conductors at the same time even if it is GFCI protected.

The American Society of Home Inspectors published a report in 1999 stating that 21% and 19% of all newly-manufactured GFCI circuit breakers and receptacles fail and leave the energized circuits unprotected. The percentage is even higher in lightning-prone areas. For example, the failure rate crosses 50% in southwest Florida where high-lightning activities are regular phenomena.

So, why the GFCI outlets fail?

Every GFCI unit has internal transient voltage surge protectors that safeguard the outlet’s sensing circuit. A damage to them leaves the switching contacts locked, which makes the GFCI allowing power supply without protection.

Incorrect wiring is another reason. The terminals in the outlets are clearly labeled as ‘Line’ and ‘Load’. You have to attach the wire springing at the breaker to the ‘Line’ while ‘Load’ is for the wire connecting downstream. If the wires don’t get connected to the right terminals, the outlet won’t work.

The Final Words

GFCI outlets make the areas in your home safer that can be potentially dangerous when exposed to electricity. Their fast-reacting time is extremely helpful in saving lives. Purchase them from a reputable electric supplier to ensure that the products are good-quality, and don’t fail to protect from energized circuits. Also, you should regularly check the outlets to make sure that they are working. An operational GFCI will turn off the power to the connecting load upon pressing the ‘test’ button on it. The U.S. Consumer Product Safety Commission (CPSC) also recommends that you should check the GFCIs at least once a month and after any power outage.

This blog is made available for educational purposes ONLY, and is not intended to provide any advice as to product selection, specifications, or appropriate uses. We assume no liability for any loss or damage resulting from one’s reliance on the material provided. Please note that such material is not updated regularly and that some of the information may not be current. We do not control or endorse and are not responsible for third-party websites linked herein.

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