A fast acting switching mechanism for a circuit breaker includes a drive rod articulated to a drive module and supporting at an end thereof a contact bridge having at opposite ends thereof respective moveable contacts for switchably engaging a pair of fixed contacts of the circuit breaker. A contact spring unit is operatively coupled to the drive module for applying closing pressure in the order of 200 Kg; and a latch latches the drive rod in an open or closed position after operation of the circuit breaker and prevents rebounds. The contact bridge includes a pair of side conductors supporting on upper edges thereof an armature having an exposed upper surface that supports the moveable contacts at opposite ends of the armature; and a reinforcing element inserted between the side conductors.