Arc-Fault Circuit Protection

An arc-fault circuit interrupter (AFCI) is a recently developed electrical safety device for homes that provides enhanced protection from fires resulting from unsafe home wiring conditions. The 2002 edition of the National Electrical Code now requires AFCIs for bedroom circuits in new residential construction. AFCIs can be installed in any 15- or 20-ampere branch circuit in a home and are currently available as circuit breakers with built-in AFCI features. In the near future, other types of devices with AFCI protection will be available.

Many people are familiar with a “short circuit,” which is a type of fault that occurs when two conductors of an electric circuit touch each other. The current flow caused by a short circuit is usually high and rapid and is quickly detected and halted by conventional circuit protective devices, such as fuses or circuit breakers. An arc fault, however, is characterized by the low and erratic flow of electricity. Due to these types of characteristics, arc faults occurring in damaged electrical cords or cable can continue undetected by conventional circuit protective devices. This leads to hazardous situations such as igniting of nearby combustible materials.

Some Typical Causes of Dangerous Arcing Faults

Damaged, abused, or worn extension cords can pose an arcing situation.

A nail from a picture hanger can break the insulation and cause arcing.

For more examples of hazardous situations, please refer to the end of the fact sheet.

The Consumer Products Safety Commission recently reported that more than 451,000 residential fires occur every year and over 1/3 of these are the result of electrical system problems. According to U.S. Department of Commerce figures, these electrical fires cause some 350 deaths, 1,700 injuries, and $700 billion in property damage annually. Many of these fires can be directly related to an arc fault.

According to the pie chart below, as many residential electric-related fires are started by the electrical circuitry as from the electric appliance itself. The exposed electric cables that run throughout a home, as well as the electric cords of appliances, are all subject to abuse and can cause arc faults.

Where Fires Occur in the Home by Zone

The National Electrical Code (NEC) recognized the potential for arc-fault occurrence and has incorporated an important requirement in Section 210-12 of the 2002 edition of the NEC. It is important to note that this NEC requirement took effect on January 1, 2002. This section is entitled “Arc-Fault Circuit Interrupter Protection.”

Section 210-12 of the NEC requires that arc-fault circuit interrupter (AFCI) protection be provided on branch circuits that supply outlets (receptacle, lighting, etc.) in dwelling unit bedrooms. This requirement is limited to 15- and 20- ampere 125-volt circuits. There is no prohibition against providing AFCI protection on other circuits or in other locations besides bedrooms. Because circuits are often shared between bedrooms and other areas such as closets or hallways, providing AFCI protection on the complete circuit would comply with 210-12.

Since cables between the electrical panel and the end appliance are subject to arc faults, protection is needed at the source of the electrical supply. AFCI protective devices are now available as part of the circuit breaker construction. AFCIs should not be confused with ground-fault circuit interrupters or GFCIs. These AFCI circuit breakers look similar to GFCI circuit breakers. They both have a white wire, which needs to be fastened to the panel’s neutral, and feature a “test” button on the circuit breaker itself. While both AFCIs and GFCIs are important safety devices, they have different functions. AFCIs are intended to address fire hazards; GFCIs address shock hazards. Combination devices that include both AFCI and GFCI protection in one unit may soon be available.

Connection Diagram: Wiring an Arc-Fault Circuit Breaker

A. Connect the coiled, white "pigtail" wire from the circuit breaker to the panel or enclosure neutral bus terminal and secure tightly.

B. Connect the white (neutral) load wire to the terminal side of the circuit breaker identified with a white mark.

C. Connect the black (hot) load wire to the remaining circuit breaker terminal marked "LOAD."

More Typical Causes of Dangerous Arcing Faults

When furniture is pushed up against or rests on a cord, the deterioration of the insulation may be greatly increased. These damaged cords then become a potential condition for arcing.

Cords that get caught in door jambs. The constant action of opening and closing can deteriorate the cable insulation, allowing arcing to occur.

Arcing to ground can occur in a wall plug or switch that was not properly installed or where connections become loose.