Same wall, different jobs

GFCI: current going the wrong way

Compares hot and neutral current; trips at a 4–6 mA imbalance. Protects people from shock and, in the 30 mA European form, property from ground-fault fires. Required by NEC 210.8 in the wet and damp places of a building.

AFCI: a spark inside the wall

An arc-fault circuit interrupter listens to the current waveform for the signature of arcing — a loose terminal, a nail through a cable, a cord crushed under a bed leg — and opens before the arc ignites what is around it. It protects the building. NEC 210.12 has required it in dwelling bedrooms since the 1999 edition and in most living areas since 2014. It does nothing about a shock through a person, and a GFCI does nothing about a series arc; the two are not substitutes.

Surge: a spike riding in

A surge protective device (SPD, UL 1449) clamps a voltage transient — lightning nearby, a utility switching event, a big motor stopping — to a level equipment survives. Type 1 and 2 sit at the service or panel; Type 3 is the strip on the floor. Since the 2020 edition NEC 230.67 wants a Type 1 or 2 SPD at every dwelling service. A surge device does not sense current imbalance or arcing.

Combining them

Dual-function AFCI/GFCI receptacles and breakers exist for the rooms that need both (a kitchen, a laundry, a finished basement). A portable GFCI cord in front of a surge-protected strip gives a workbench all three: the panel's SPD, the strip's Type 3 clamp, and shock protection at the tool.