AFCI (Arc-Fault Circuit Interrupter)
CSI Division 26, Electrical
A protective device that detects the specific electrical signature of a dangerous arc, such as a nail accidentally driven through a cable, and shuts the circuit off before that arc can start a fire, required by code in most living spaces and, separately, on DC circuits for rooftop solar systems.
Why it matters
A standard breaker reacts to overload or a short, but a dangerous arc can occur without ever drawing enough current to trip a normal breaker. AFCI protection is built to recognize the specific pattern an arc creates and react to that pattern directly, closing a fire-risk gap that ordinary circuit protection doesn't cover.
On a real project
An electrician wiring a bedroom circuit installs an AFCI breaker at the panel, a requirement in most living spaces, so that a damaged cable behind the wall, one that might otherwise smolder undetected, trips the circuit before it can start a fire.
Who this matters most to
An Electrician installs AFCI protection on every circuit code requires it for, and a Solar Installer relies on the same AFCI principle on the DC side of a rooftop solar array, where a damaged panel connection creates a similar arc-fault risk.
Where this goes wrong
A remodel adds a new bedroom circuit from an older subpanel that doesn't have AFCI protection, assuming the rest of the house's wiring sets the standard for what's required. The gap is caught during inspection, since current code requires AFCI on that new circuit regardless of what protection exists elsewhere in the house.