Abstract: In the cut-on position of the protective switch a movable contact element engages with a stationary contact element and at the same time is exposed to the action of a force displacing such movable contact element into a cut-off position. The movable contact element is arrestable in the cut-on position by means of a locking device which can be activated by an excess current. In order to reduce the number of movable parts to a minimum as well as to avoid parts which generate heat due to appreciable thermal losses, such locking device is provided with a substantially U-shaped locking element formed of a soft magnetic material. This locking element surrounds the movable contact element with play or clearance and is displaceably mounted transversely with respect to the flow of current in such movable contact element. At least one free leg end of the locking element is provided with a stop which in the cut-on position cooperates with a stop nose which is movable together with the movable contact element.

Abstract: A gas-blast switch having a hollow support insulator, and and at least one switching chamber housing supported thereon and within which there is arranged a set of fixed contacts, surrounded by a blast chamber, and a set of movable contacts. A blast nozzle coacts with the movable contacts and is connected with a pump device having a pump cylinder surrounding a pump chamber and movable with the movable contacts. The pump cylinder is displaceably arranged upon a stationary piston. A check valve opens towards the pump chamber. During the cut-on stroke pressurized gas is sucked by the valve into the pump chamber. The latter is connected by the check valve with a supply compartment communicating via inlets with the blast chamber and the internal space of the support insulator. A further valve is responsive to the pressure increase in the blast chamber, which valve, when responsive, interrupts the connection between the internal space of the support insulator and the inlets.