Abstract: A multipolar circuit breaker having a lower case portion with side frame plates and a central frame plate facing the side frame plates on its two major sides, the central frame plate having a deep central groove which forms two flexible central frame plate arms each facing one of the side frame plates to form a nacelle sized to receive one of the switching mechanisms, each of the side frame plates and the arms of the central frame plate having, proximate to its free end, at-least-one inwardly facing protrusion, each of which is in a position opposed to the corresponding protrusion on the companion plate forming the nacelle and, after the respective switching mechanisms are installed, overlapping the side plates of each of the switching mechanisms, the arms of the central frame plate having been deflected to permit insertion of each switching mechanism, deflection in testing or use being prevented by inserting a high dielectric strength plastic stiffener in the groove separating the arms in the central frame p

Abstract: A circuit breaker has an insulated casing including an upper casing portion and a lower casing portion. A switching mechanism is attached to a frame which is seated in a positioning recess portion of the lower casing portion. The frame and switching mechanism are captured by extending support arms of the lower casing portion and are fixedly secured thereto to permit operation of the switching mechanism prior to final assembly of the upper and lower casing portions.