Switch for automatically interrupting a circuit when its contacts are

Abstract

A safety switch for automatically interrupting a circuit when its main contacts are fused or stuck together in the 'ON' position comprises a housing containing a pair of main contacts and auxiliary safety contacts which are normally closed but are automatically opened when the main contacts fuse together. One main contact is an 'ON' contact, and the other main contact is carried by a movable switch arm. A first spring in the housing mechanically coupled to the movable switch arm normally urges the movable main contact into open position away from the engagement with the ON contact. Switch operating means include a movable actuator to overcome the biasing force of the spring for moving the movable main contact to closed position into engagement with the ON main contact for energizing a circuit controlled by the main contacts. The auxiliary safety contacts become opened in response to abnormal movement of the switch arm under influence of the spring when the actuator is moved to OFF position, but the movable main contact remains fused or stuck to the ON main contact. In their operation, a second pre-stressed spring continuously biases the auxiliary safety contacts toward open position, and they are automatically triggered and immediately are moved from closed to open position by this pre-stressed spring for interrupting the controlled circuit when the actuator is moved to Off position but the main contacts remain fused or stuck together in ON relationship.