Molded case circuit breaker can be cut off after the current exceeds the trip rating of the current .Molded case refers to the plastic insulation shell as a unit, used for isolation between a conductor and grounded (earthed) metal parts .Molded case circuit breakers usually contain thermal magnetic tripping unit, and a large number of molded case circuit breaker can be equipped with solid state trip sensors .The tripping unit is divided into: thermal and electronic magnetic tripping the trip Commonly used, the rated current of the following 15, 25 and 30 and 40 to 50 60, 75, 80, 100, 125, 160, 200, 225, 250, 315, 350, 400, 500, 630 A.