The term arc fault refers to a situation in which loose or corroded wiring connections create an intermittent contact that causes electrical current to spark, or arc, between metal contact points. When you hear a light switch or outlet buzzing or hissing, you are hearing arcing as it happens. This arcing translates to heat, which can break down the insulation surrounding individual conducting wires, providing the trigger for electrical fires. Hearing a switch buzz does not mean the fire is necessarily imminent, but it does mean there is a potential danger that should be addressed.
The term arc-fault protection refers to any device that is designed to guard against this problem.
Arc Fault vs. Short Circuit vs. Ground Fault
The terms arc fault, ground fault, and short-circuit are sometimes confused to mean the same thing, but they actually have different meanings, and each requires a different strategy for prevention.
A short-circuit refers to any situation in which energized "hot" current strays outside the established wiring system and makes contact with either the neutral wiring pathway or the grounding pathway. When this happens, the flow of current loses its resistance and suddenly increases in volume. This quickly causes the flow to exceed the amperage capacity of the circuit breaker controlling the circuit, which normally trips to stop the flow of current.
A ground fault refers to a specific type of short circuit in which energized "hot" current makes accidental contact with a ground. In fact, a ground fault is sometimes known as a "short-to-ground." Like other types of short circuits, circuit wires lose resistance during a ground fault, and this causes an unimpeded flow of current that should cause the circuit breaker to trip. However, the circuit breaker may not operate fast enough to prevent shock, and for this reason, the electrical Code requires special protective devices, known as GFCIs (ground-fault circuit interrupters) to be installed in locations where ground faults are most likely to occur, such as outlets near plumbing pipes or in outdoor locations. Because these devices sense power changes very fast, they can shut down a circuit even before a shock is felt. GFCIs, therefore, are a safety device intended mostly to guard against shock.
An arc fault, as mentioned above, is when loose wire connections or corroded wires cause sparking or arcing, which may create heat and the potential for electrical fires. It may be a precursor to a short circuit or ground-fault, but in and of itself, an arc fault may not shut down either a GFCI or a circuit breaker. The normal means of guarding against arc faults is an AFCI (arc-fault circuit interrupter)—either an AFCI receptacle or an AFCI circuit breaker. AFCIs are intended to guard against the danger of fire.
Code History of Arc Fault Protection
The National Electrical Code, revised every three years, has gradually increased its requirements for AFCI protection on circuits. In 1999, the Code began requiring AFCI protection in all circuits feeding bedroom outlets, and beginning 2014, nearly all circuits supplying general outlets in living spaces are required to have AFCI protection in new construction or in remodeling projects.
As of the 2017 edition of the NEC, the wording of Section 210.12 states:
All 120-volt, single-phase, 15- and 20-ampere branch circuits receptacles or devices installed 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 shall be protected by AFCIs.
Normally, circuits receive AFCI protection by means of special AFCI circuit breakers that protect all outlets and devices along the circuit, but where this is not practical, there are also AFCI receptacles that can be used.
AFCI protection is not required on existing installations, but where a circuit is extended or updated during remodeling, it must then receive AFCI protection. Thus, an electrician who works on your system is obligated to update the circuit with AFCI protection as part of any work he does on it. In practical terms, it means that virtually all circuit breaker replacements will now be made with AFCI breakers in any jurisdiction that follows the NEC (National Electrical Code).
Not all communities comply with the NEC, however, so check local authorities for requirements regarding AFCI protection.
A GFCI Is Not an AFCI
It is important to understand that an AFCI does not take the place of GFCI protection. While ground-fault circuit interrupters protect against shock, they are not intended to protect against fire, as does an AFCI. Thus, in new or remodeled wiring, many locations will require both GFCI and AFCI protection. This can be accomplished by installing AFCI circuit breakers then using GFCI receptacles at specific locations; or, there are combination AFCI/GFCI circuit breakers that can offer both types of protection to the entire circuit.
It is critical that Code requirements for both AFCI and GFCI protection are followed whenever extending or updating a wiring system.