Abstract: A bent roundabout current path (8d) rising in the shape of an inverted U is formed between a horn portion (8a) and the end portion of a fixed contact (1) where an arcing horn (8) is joined to the fixed contact (1). An arc (12) is subjected to the electromagnetic force directed to an arc-extinguishing chamber side from the magnetic field H of an current I flowing through the arc-(12)-side conductor portion of the roundabout current path (8d). Therefore, the moving-contact-(4)-side foot of the arc (12) is retained in the leading end portion of the moving contact (4) and not returned to the movable contact (3) side.

Abstract: In a circuit breaker, a grid support (12) having a pair of side walls (12a) which are confronted with each other, is provided by molding resin, and arc-extinction grids (6) are inserted into grooves formed in the side walls (12a). The grid support is fixedly mounted on the stationary contactor (1) by fitting legs (12c) protruded from the bottom surfaces of the side walls (12a) into a U-shaped hole (9) formed in the stationary contactor (1) which defines outside current paths (1a) and an inside current path (1b). The upper surfaces of the outside current paths (1a) are covered with the side walls (12a), respectively, and the upper surface of the inside current path (1b) except for a stationary contact (3) is covered with the cover plate (12b) through which the side walls (12a) are connected to each other.