One or more master CHN 21AM and one or more back-up CHN 21AC are provided. The printed circuit board includes an insulation layer and a conductor layer having a GND pattern. An interconnect bump may be formed on a larger contact pad, the bump having a large diameter. The protective layer does not contact with atmospheric carbonic acid gas, preventing alteration thereof. When the device is plugged into a receptacle of the branch circuit, the breaker switch can then be turned on, resulting in a short-circuit, which de-energizes the branch electrical circuit. The wiring cord cover is mounted detachably to the apparatus body in a state where the wiring cord cover has the wiring cord disposed therein.