125V AC only, 3 fuses. The combination of Type S fuse and matching adapter make it impossible to over fuse a circuit. Type S plug fuses and matching adapters of the same amperage have special mating screw threads or barriers to prevent mismatching. Adapters fit standard Edison screw base fuse holders. A special feature permanently locks the adapter in place so that only a fuse of the same amperage can be used. Type S fuses are time delayed, so that is they will not blow needlessly when minor overloads or surges of short duration occur. Responds quickly to short circuits or heavy overloads (Blown fuse is indicated of window darkens or there is a visible break in link.)