AFCI – Arc Fault Circuit Interrupters

by Nick Gromicko, CMI®, Kenton Shepard, and Joe Boos, CPI

Arc-fault circuit interrupters (AFCI) are particular types of electrical receptacles or overcurrent protection devices designed to detect and respond to potentially dangerous electrical arcs in home branch wiring.

AFCI, how do they work?

AFCI function by monitoring the electrical waveform and promptly opening (interrupting) the circuit they serve if they detect changes in the wave pattern characteristic of a dangerous arc. They also must be capable of distinguishing safe, typical arcs, such as those created when a switch is turned on or a plug is pulled from a receptacle from arcs that can cause fires. An AFCI can detect, recognize, and respond to very small changes in wave patterns.

What is an arc?

When an electric current crosses an air gap from an energized component to a grounded component, it produces a glowing plasma discharge known as an arc. For example, a lightning bolt is a huge, powerful arc that crosses an atmospheric gap from an electrically charged cloud to the ground or another cloud. Just as lightning can cause fires, arcs produced by domestic wiring can produce high levels of heat that can ignite their surroundings and lead to structure fires.

Where are arcs likely to form?

Arcs can form where wires are improperly installed or when insulation becomes damaged. In older homes, wire insulation crystallizes as it ages, becoming brittle and prone to cracking and chipping. Damaged insulation exposes the current-carrying wire to its surroundings, increasing the chances that an arc may occur.  Situations in which arcs may be created:

• Electrical cords damaged by vacuum cleaners or trapped beneath furniture or doors.
• Damage to wire insulation from nails or screws driven through walls.
• Appliance cords damaged by heat, natural aging, kinking, impact or over-extension.
• Spillage of liquid.
• Loose connections in outlets, switches, and light fixtures.

Where are AFCI devices required?

Ask a qualified electrician or the local authority which AFCI requirements apply to the home and the proposed work. Requirements depend on the adopted code, amendments and project scope. A general home inspection is not a comprehensive code-compliance certification.

What types of AFCI devices are available?

AFCIs are available both as circuit breakers for installation in the electrical distribution panel or as point-of-use receptacles installed in the wall just like a normal receptacle.
The protection provided depends on the device type and correct installation. Consult the manufacturer’s instructions and a qualified electrician rather than assuming every AFCI configuration has identical coverage.

AFCI Nuisance Tripping

Repeated tripping needs investigation by a qualified electrician. Do not assume a trip is harmless or bypass the protection to keep equipment running. Note which devices were operating and follow the manufacturer’s instructions for testing and reset procedures.

Arc Faults vs. Ground Faults, what’s the difference?

It is important to distinguish AFCI devices from Ground Fault Circuit Interrupter (GFCI) devices. GFCIs respond to an imbalance between outgoing and returning current that can indicate current flowing along an unintended path.

GFCIs reduce electric-shock risk, while AFCIs reduce the risk of fires associated with dangerous arcing. A neutral conductor is not the equipment grounding conductor. Neither device guarantees protection from every electrical hazard. Consult a qualified electrician about the correct device and installation for the circuit.

See the manufacturer-supported AFCI Safety explanation and CPSC’s AFCI guidance.