Three forms
- Plug-head: the GFCI is the plug. Everything downstream — the whole cord and the tool — is protected; TEST and RESET are at the wall. The default for tools, heaters and anything on an extension lead.
- In-line: a sealed module partway down the cord, reachable at the machine, so a reset does not mean a walk to the outlet. Common on equipment leads, hard-wired pigtails and wash-down gear.
- Rewireable (user-attachable): a plug-head or in-line GFCI with screw terminals, fitted to a cord you already have, matched to its gauge (the three ratings).
Where they count
NEC 590.6(B) accepts listed cord sets with GFCI protection for temporary power; OSHA 1926.404(b)(1) is satisfied by them on a job site; NEC 422.5 appliances often carry one from the factory. In a home they are the answer for a garage freezer, a pond pump, a window unit on an unprotected outlet, or a 240 V machine whose circuit has no two-pole GFCI breaker.
Reset behaviour
Manual reset stays off after a trip or a power cut until someone presses RESET — tools, heaters, saws, anything that must not restart alone. Automatic reset returns when power does — refrigeration, sump and pond pumps, telecom and medical gear that must not stay dead (the full comparison).
What they are not
Not a substitute for the receptacle the Code requires in a bathroom or kitchen — the inspector wants the installed device. Not an overcurrent device. And a portable GFCI at the tool end of a long cord protects only the tool; put it at the source end.
Ratings
Class A, UL 943 listed, 15 or 20 A, 120 V or 240 V, on NEMA 5-15, 5-20, 6-15, 6-20, L5 and L6 plugs (which plug); 30 mA and 10 mA RCD versions for export (RCD cords).