AFCI vs GFCI

A GFCI guards against shock by watching for current leaking off the circuit; an AFCI guards against fire by listening for the signature of arcing. They answer two different dangers with two different kinds of detection, and some devices carry both.

Two hazards, two detectors

A ground fault is current finding a way back that it should not — through a wet surface, a failed appliance, a person. The GFCI compares what leaves on the hot with what returns on the neutral, and the instant they stop matching it opens. That imbalance is the tell of a shock path, and speed is everything, so it trips in a fraction of a second.

An arc fault is different. A loose terminal or a nicked conductor can arc — sputter and spark across a tiny gap — and that arc throws heat exactly where the wiring is already damaged, which is how electrical fires start. An AFCI does not care about leakage; it listens to the shape of the current and picks out the ragged, repeating signature of a fault arc from the clean, brief sparks that normal switching makes. When it hears the dangerous pattern, it opens the circuit. Where a location needs protection from both hazards, a combination device does both jobs at once.

Questions people ask

What is the difference between AFCI and GFCI?

A GFCI protects against shock: it watches for current leaking off the circuit and opens fast. An AFCI protects against fire: it listens for the electrical signature of arcing in damaged wiring. Different hazard, different detection, sometimes both in one device.

Does a GFCI protect against fire, or an AFCI against shock?

Not really — each is tuned to its own hazard. A GFCI will not notice an arc that stays on the circuit, and an AFCI will not catch a leakage path through a person the way a GFCI does. Where you need both, you use a device that does both.

How does an AFCI tell a fault arc from a normal spark?

By the pattern. A switch closing or a motor brush sparks in a clean, brief way; a damaged connection arcs with a ragged, repeating electrical signature. The AFCI is built to recognise the dangerous pattern and ignore the harmless ones.

GFCI wiring diagram — see the line/load split and a trip.
Bonding vs grounding
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