Abstract: A molded case circuit breaker is provided with ground fault protection by a modular unit which drops into a pole compartment in the molded casing in place of a pole assembly. The modular unit includes a housing forming an open faced cavity across which is mounted a printed circuit board with the ground fault circuit components and trip solenoid projecting into the cavity. The housing also supports the ground fault sensing toroid in a position for the appropriate conductors to pass through the coil. A bell switch and auxiliary switch are positioned by the housing for actuation by levers mounted on the cradle pin and crossbar, respectively. An integral leaf spring molded into the housing accommodates for manufacturing tolerances and fixes the positions of the various components.

Abstract: The movable contact arms of a circuit breaker are latched in the blow open position to prevent rebound and possible restrike of the arc in response to the very high magnetic repulsion forces generated by a short circuit in the protected electrical system. Each movable contact arm is mounted on a secondary carrier coupled to a main carrier by a spring loaded cam mechanism which allows the movable contact arm to blow open before the main carrier is rotated to the open position by the spring driven circuit breaker operating mechanism. In one embodiment of the invention, the movable contact arm is latched in the blow open position by a latching detent in the cam surface of the cam mechanism. In a preferred embodiment, the secondary carrier is latched by a detent formed by a leaf spring cantilevered from a fixed support. Subsequent rotation of the main carrier by the operating mechanism releases the latch by rotating the secondary carrier clear of the detent formed by the leaf spring.