Abstract: A molded case circuit breaker having current limiting capabilities optimized for relatively smaller frame sizes. More specifically, one aspect of the invention relates to a two-piece carrier assembly for carrying the main and arcing contact arms which allows the main and arcing contacts to be blown open during short circuit conditions. The two-piece carrier assembly includes an inner carrier and an outer carrier pivotally connected together. The contact arms are carried by the inner carrier. When sufficient magnetic repulsion forces are exerted on the contacts due to a short circuit condition, the inner carrier pivots relative to the outer carrier to allow the contact arms to blow open. In order to control the amount of force required for blow open, a compression spring loaded cam assembly is provided.

Abstract: A positive off mechanism for a circuit breaker includes a pair of positive off levers slideable in slots in the side plates and extendable into the path of the operating handle to prevent movement of the handle to the off position when the contacts are welded closed. The positive off levers are actuated by positive off links pivotally mounted to the side plates and coupled to the positive off levers by "dog bone" connections. The positive off links in turn are actuated by the toggle mechanism of the circuit breaker which collapses to open the contacts during normal circuit breaker operation, but which remains erect when the contacts are welded closed.