Home Improvement Skills & Specialties Electrical Wiring & Circuits

Understanding Arc Faults and AFCI Protection

Now Required for Most Circuits

The term "arc fault" refers to a situation in which loose or corroded wiring connections create an intermittent contact that causes an 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.

Close up of two naked wires
Ernesto r. Ageitos / Getty Images

What Causes an Arc Fault

An arc fault is essentially caused by stressed electrical wiring or devices. This can include equipment or wiring that is damaged or overheated. When current flows through an unwanted path, an arc fault can occur. This process generates intense heat, which can ignite nearby materials such as wood framing or insulation.

How is an Arc Fault Detected?

An arc may occur due to various reasons such as damaged electrical conductor insulation, which can be quite dangerous. To prevent any harm, AFCI (Arc Fault Circuit Interrupter) devices analyze the characteristics of the event and determine if it is hazardous. Manufacturers of AFCI test for hundreds of possible operating conditions and program their devices to constantly monitor for normal and dangerous arcing conditions.

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 National 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, occurs 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 outlet 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 arc-fault protection on circuits.

What Is Arc-Fault Protection?

The term "arc-fault protection" refers to any device that is designed to guard against faulty connections causing arcing, or sparking. A detection device senses the electrical arc and breaks the circuit to prevent an electrical fire. Arc-fault protection devices keep people safe and are essential for fire safety.

In 1999, the Code began requiring AFCI protection in all circuits feeding bedroom outlets, and beginning in 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 supplying outlets 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 outlets 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.

Why Do You Need Arc Fault Circuit Interrupters (AFCIs)?

Like smoke alarms, fire extinguishers, and other emergency equipment, AFCIs are designed to detect various arcing electrical faults so that the risk of fire can be drastically reduced. Electrical fires can be a silent killer in the home and do extensive damage. The AFCI detects even low-level hazardous arcing currents and shuts down the circuit before an electrical fire has a chance to spark.

How Does an AFCI Work?

Advanced electronic technology is used to detect "normal" and "dangerous" arcing conditions in the circuit. Some household equipment, such as motor-driven vacuum cleaners or furnace motors, naturally create arcs, which are considered normal. Another normal arcing condition occurs when a light switch is turned off, and the opening of the contacts creates an arc. An AFCI will sense these abnormal arcs, determine if they're dangerous, and de-energize the circuit before it becomes hazardous.

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 and 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.

FAQ
  • What is the difference between GFCI and AFCI?

    Two types of safety outlets can protect you and your home. A GFCI outlet trips when it senses a short to ground, while an AFCI outlet trips when an arc fault is detected. GFCI protection will prevent electrical shocks by cutting off the electric current when it travels to the ground unintentionally. AFCI protection is designed to prevent fires by monitoring electrical currents and stopping the electricity flow when it picks up on unwanted arcing patterns.

  • How do you fix an arc fault?

    You can attempt to troubleshoot an arc fault yourself. First, unplug everything in the circuit. Next, plug in and turn on each device one by one to determine which one is tripping the breaker. Check this device and see if there are broken chords or damaged wires, and if it's compatible with the breaker. Depending on if you can isolate the problem and what it is, you may be able to address it yourself or call a licensed electrician.

  • What causes an arc fault to the ground?


    An arc fault to ground or short to ground occurs when an energized current accidentally makes contact with a ground path. Electricity will always seek a path to ground. When this unintentional path is a person's body it may result in severe shock or even be fatal.

  • What would cause an arc fault breaker to trip?

    Several different conditions can cause an arc fault breaker to trip. They include poor connections, overloaded circuits, dampness or mold, and appliances or devices that are incompatible.

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  1. Home Fire Caused by Electrical Failure or Malfunction. National Fire Protection Association.

  2. National Electrical Code, 2023. National Fire Protection Association.

  3. What is a GFCI? U.S. Consumer Product Safety Commission.

  4. What is an AFCI Circuit Breaker? National Electrical Manufacturers Association.

  5. 210.12 Arc-Fault Circuit-Interrupter Protection. National Electric Code 2020 of Illinois.

  6. Where Arc-Fault Circuit-Interrupter (AFCI) Protection is Required in Residential Dwelling Units. New York Electrical Inspection Agency.

  7. AFCI and GFCI Requirements. National Association of Home Builders.