In the world of electronics, AFCI stands for “Arc-Fault Circuit Interrupter.” An AFCI is a special type of electrical receptacle, outlet or circuit breaker designed to detect and respond to potentially dangerous electrical arcs in home branch wiring.

afci-inspectionArcs and Arc Faults

An electrical arc can happen when electricity “jumps” a gap in a circuit or between two conducting electrodes. When the gap is a gas, such as the air, the rapidly moving electrons that have jumped between the electrodes produce a glowing plasma discharge, known as an arc. For example, a bolt of lightning is a very large and powerful arc that crosses an atmospheric gap from one electrically charged cloud to the ground or to another cloud.

An arc fault can occur when electric current flows in an unintended path. In the home, this can happen in the structure’s electrical system due to corroded or faulty wiring, or because of insulation that has deteriorated due to age, accident or misuse. Instead of the electricity flowing in an uninterrupted route between the electrodes, it “escapes” into the surrounding air in the form of an arc.

An arc fault is dangerous because the heat generated at the point of the arc can reach a temperature of up to 10,000 degrees Fahrenheit. Just as lighting can cause fires, the intense heat produced by an arc in the home can create burning particles that can then ignite key structural components of the structure. Even more than short-circuits and overloads, arc faults are the leading causes of the 40,000 electrical wiring fires that occur each year in the United States. These fires result in hundreds of deaths and thousands of injuries, annually, as well as hundreds of millions of dollars in damage.

In older homes especially, wire insulation normally tends to crystallize over time, becoming brittle and prone to cracking and chipping. This damaged insulation exposes the wire to its surroundings, increasing the chances of an arc fault occurring. But other situations can also increase the possibility of an arc fault, including:

  • Electrical cords that are damaged or trapped beneath furniture or doors
  • Damage to wire insulation in walls from nails or screws driven through them
  • Appliance cords damaged by heat or abuse
  • Liquid spills that corrode insulation
  • Loose or faulty connections in outlets, fixtures and switches

How AFCIs Work

AFCIs function by monitoring the electrical waveform of the circuit they are serving. When they detect changes in the wave pattern that are characteristic of a dangerous arc, they open their internal contacts in order to de-energize the power in time, preventing an arc from starting a fire. Unlike fuses or conventional circuit breakers, which only respond to sustained overloads and short circuits, AFCIs’ advanced electronics are sophisticated enough to detect, recognize and respond to very small changes in electrical wave patterns within milliseconds. They can also tell the difference between a harmless arc, such as those created when a switch is turned on or a plug is pulled from a socket, from a dangerous one.

There are three types of AFCIs:

  • Branch/feeder AFCIs are the most common type. They replace standard circuit breakers in a home’s electrical panel box and provide arc fault protection throughout the entire home wiring system from the panel box to the home’s electrical outlets
  • Outlet AFCIs are receptacles that provide protection to power cords plugged into them
  • Combination AFCIs combine the features of both branch/feeder and outlet AFCIs and are capable of detecting faults in the complete system from the panel box to plugged-in appliances

AFCI Requirements

In 2008, the National Electrical Code (NEC) required that AFCIs be installed in all circuits that feed outlets in the bedrooms of newly built homes. The 2014 version of the NEC now requires combination AFCIs to be installed on all branch circuits supplying outlets or devices in dwelling unit kitchens, family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, laundry areas, or similar rooms or areas. While AFCIs offer great protection against home electrical fires, they are not required in every state or jurisdiction. However, many states and municipalities have incorporated their use into their local building codes. AFCIs can also be retrofitted for older homes that may benefit from the added protection against the arcing faults that can occur in aging wiring systems.

AFCIs should only be installed by a licensed electrician as their installation involves working within electrical panel boxes that are usually live, even when the main circuit breakers are turned off. Properly installed AFCIs should also preclude the possibility of “nuisance tripping” which can sometimes occur when an AFCI activates in a situation that is not dangerous, causing an unnecessary or needless power outage.


Arc Faults vs. Ground Faults

AFCIs should not be confused with GFCIs, or Ground Fault Circuit Interrupters. AFCIs are designed to protect branch circuit wiring from arcing faults that can start an electrical fire. GFCIs are designed to protect against the consequences associated with electric shock when current leaks from a hot, or ungrounded, conductor to a grounded object. If that object happens to be a person who unintentionally becomes the current’s path to the ground, a harmful, or even fatal, electrocution may occur.

GFCIs monitor the current flow between hot and neutral (grounding) conductors and activate when they sense of difference as small as 5 milliamps. GFCIs first appeared in the1960s and are normally used in bathrooms, kitchens, garages, basements, and outdoor receptacles where the potential for a short circuit resulting from a ground fault in an electric appliance or tool is a potential hazard. For maximum defense against both accidental electrical fires and shocks, it is possible to install combination devices that include both AFCI and GFCI protection in a single unit.