Electric switch with welded contact sensor lockout

摘要

A plunger operated switch has a pair of movable contacts on a movable contact carrier bridged by a secondary contact supported on a pushbutton operator member which is biased apart from the contact carrier. Depression of the pushbutton operator for the plunger assembly moves the primary movable contacts into bridging engagement with the stationary contacts through the secondary contact member. In the event the primary movable contacts weld to the stationary contacts and an operating force is removed from the plunger operator, a spring biases the secondary contact away from the primary movable contacts to open the bridging relationship therebetween and open the circuit controlled by the switch. A pair of normally closed contacts are arranged for operation by the pushbutton operator so that the contacts open before the main contacts close and close after the main contacts open, rendering them particularly suitable for use as dynamic braking contacts in a motor control application. Insulating means are provided between the primary movable contacts and the secondary bridging contact to prevent reclosure thereof once the secondary contact is separated from the primary movable contacts.