Abstract: A leakage current detector for an electricity supply comprising a plurality of supply conductors supplying a load, the leakage detector comprising a connection from each supply conductor to a common conductor, a circuit for detecting a differential current flowing in the connections, and a circuit arranged to provide an output signal when the differential current reaches a predetermined magnitude.

Abstract: A protective device is described for retrofitting to a wall-mounted electrical socket outlet of the kind comprising an open-fronted housing containing at least one electrical socket and a removable front plate screw-fitted to the open front of the housing and having an opening exposing said socket terminals. The protective device comprises a housing which is screw-fittable to the open-fronted socket housing in place of the original front plate and has socket terminals exposed at a front surface. The device includes a hinged flap which can be swung over the exposed socket terminals and there releasably held in place.

Abstract: An apparatus for testing an arc fault detector comprises a housing (30) having an ac power input plug (32) and an ac power output socket (34), the plug being connected to supply ac power to the socket via electrical supply conductors (L, N) inside the housing. The socket (34) allows connection of an external appliance (36) to the housing for receiving power from the plug (32) through the internal supply conductors. An arc generator (100) inside the housing is connected between the plug (32) and the socket (34). The arc generator comprises at least one pair of contacts and means to vibrate the contacts alternately open and closed.

Abstract: A leakage current detector for an electricity supply comprising a plurality of supply conductors supplying a load, the leakage detector comprising a connection from each supply conductor to a common conductor, a circuit for detecting a differential current flowing in the connections, and a circuit arranged to provide an output signal when the differential current reaches a predetermined magnitude.

Abstract: A current transformer comprises a plurality of primary conductors (L,N) passing through a ferromagnetic core (10) and a secondary winding (W1) wound on the core. The transformer further including a ferromagnetic member (T1) continuously surrounding the primary conductors between the primary conductors and the core.

Abstract: An apparatus for detecting a leakage current flowing between at least one supply conductor of a multi-conductor electricity supply to load and non load currents carrying electrical conductor nominally insulated from the supply conductor. The apparatus includes a current transformer having a primary winding and a secondary winding. The primary winding is connected between the non load current carrying conductor and at least one other supply conductor so that leakage current flowing between the at least one supply conductor and the non load current carrying conductor flows through the primary winding to the other supply conductor. An electromechanical relay has a set of normally-closed contacts in series with the electricity supply. Circuitry connecting the secondary winding of the current transformer and the relay is provided so the relay is actuated by a current induced in the secondary winding by a leakage current meeting certain criteria as to magnitude and/or duration.

Abstract: A residual current device comprises a circuit (CT, 10, 12) for detecting a current imbalance in an AC supply to a load indicative of a residual current and providing a corresponding output. A relay RLA has contacts SW1 in the AC supply to the load. The relay contacts SW1 automatically close when a closing current is passed through the relay and is thereafter maintained closed so long as a holding current, less than the closing current, passes through the relay. A capacitor C1 is connected to the AC supply in parallel with the relay RLA such that, upon application of power from the AC supply, current flows to the charge storage device. An electronic switch SCR2 in series with the relay is turned on when the voltage on the capacitor exceeds the breakover voltage of a Zener diode ZD2 to allow discharge of the capacitor through the relay to provide a current exceeding the closing current, the AC supply thereafter providing a holding current for the relay at least when the supply is at a certain minimum voltage.

Abstract: A residual current device comprises a circuit (CT, 10, 12) for detecting a current imbalance in an AC supply to a load indicative of a residual current and providing a corresponding output. A relay RLA has contacts SW1 in the AC supply to the load. The relay contacts SW1 automatically close when a closing current is passed through the relay and is thereafter maintained closed so long as a holding current, less than the closing current, passes through the relay. A capacitor C1 is connected to the AC supply in parallel with the relay RLA such that, upon application of power from the AC supply, current flows to the charge storage device. An electronic switch SCR2 in series with the relay is turned on when the voltage on the capacitor exceeds the breakover voltage of a Zener diode ZD2 to allow discharge of the capacitor through the relay to provide a current exceeding the closing current, the AC supply thereafter providing a holding current for the relay at least when the supply is at a certain minimum voltage.