Abstract: An electromagnetic switch comprises at least one pair of magnetically latchable electrical contacts (12a, 14a) operated by current flowing in an associated coil means (K1, K2), and an electrical circuit arranged to apply a first current in a first direction through the coil means to close the contacts and subsequently to apply a second current in a second, opposite, direction through the coil means to open the contacts. In certain embodiments the coil means comprises first and second independent coils (K1, K2) and the first and second currents flow in opposite direction in the first and second coils respectively. In other embodiments the coil means comprises a single coil (K1) and the first and second currents flow in opposite directions in the single coil.

Abstract: A residual current device for an AC electricity supply comprises a housing (10) and a first load conductor (L) inside the housing connected in series between the supply and a load and including a set of contacts (18) by which an electrical connection between the supply and the load may be made or broken. A current transformer is disposed inside the housing and has a toroidal core (TI) the first load conductor passing through the core and forming one primary winding of the current transformer. At least one further load conductor (N) outside the housing passes through the core (T) via an opening (32) in the housing and forms a further primary winding of the current transformer. A secondary winding (W) on the core produces an output in response to a residual current, and a circuit (RCC) inside the housing is responsive to the output on the secondary winding to open the contacts if the residual current is above a predetermined level.

Abstract: A residual current device for an AC electricity supply comprises a housing (10) and a first load conductor (L) inside the housing connected in series between the supply and a load and including a set of contacts (18) by which an electrical connection between the supply and the load may be made or broken. A current transformer is disposed inside the housing and has a toroidal core (TI) the first load conductor passing through the core and forming one primary winding of the current transformer. At least one further load conductor (N) outside the housing passes through the core (T) via an opening (32) in the housing and forms a further primary winding of the current transformer. A secondary winding (W) on the core produces an output in response to a residual current, and a circuit (RCC) inside the housing is responsive to the output on the secondary winding to open the contacts if the residual current is above a predetermined level.

Abstract: A resettable switching device, e.g. a relay, comprises a fixed contact (18) and a movable contact (28). A solenoid (12) is fixed relative to the fixed contact and a ferromagnetic plunger (20) carries the movable contact. A spring (24) biases the plunger away from the fixed contact so the device is normally open. When the device is set a further ferromagnetic element, e.g. a plunger (22), holds the first plunger (20) in a closed-contact position by magnetic attraction against the action of the spring (24). When a predetermined current condition exists in the solenoid the magnetic attraction between the element and plunger is reduced below the level necessary to hold the plunger so that the movable contact disengages the fixed contact.

Abstract: A circuit breaker has at least one pair of electrical contacts of which one contact is mounted for movement relative to the other contact between first and second positions. One of the first and second positions corresponds to the contacts being closed and the other corresponds to the contacts being open. Resilient biassing means urges the one contact into the first position so as to maintain the contacts normally in the condition corresponding thereto. A magnet (such as a solenoid acting in active or passive mode) is capable of holding one contact in the second position against the action of the resilient biassing means, but is demagnetisable to permit the one contact to return to the first position.