Circuit breaker

A circuit breaker comprising:

• first and second fixed contact devices disposed at each pole and insulated from each other, said first and said second fixed contact devices having first and second fixed contacts respectively;
• a movable contact arm having first and second movable contacts which are respectively associated with said first and said second fixed contacts, said movable contact arm bridging between said first and said second fixed contacts in a closed circuit state to flow current in an opposite direction to the current which flows near said first and said second fixed contacts;
• a supporting rod having said movable contact arm at one end thereof, and being supported so that it can be guided to open or close a circuit;
• a cross bar having arms insulated at every pole, said cross bar controlled to be capable of opening-closing the circuit and tripping by means of a trip-free mechanism;
• a movable contact link whose one end is rotatably supported on said arms and whose other end is rotatably connected to the other end of said supporting rod;
• a toggle spring supported so as to constitute a dead center link mechanism between said arms and said movable contact link so that said movable contacts can press on said fixed contacts in a closed circuit state;
• a trip bar being common to all poles, said trip bar making a latch mechanism in said trip-free mechanism do the tripping action;
• and
• a set of electromagnetic devices in which a winding passing the current of a main circuit is wound, wherein a movable portion in said electromagnetic device has a first portion which engages a part of said trip bar to release a trip mechanism, and second portion which engages said supporting rod to open said movable contact arm to the vicinity of dead center, and wherein said movable contact arm has a position of stop of opening said contacts at which the force of said toggle spring reverses over said dead center, and wherein, during a short-circuit, an electromagnetic repulsive force generated between said fixed and said movable contacts and an attaction force of said electromagnetic device directly open said movable contact arm to said position of stop of opening against the contacting force of said toggle spring to break the circuit.