Abstract: A circuit breaker-includes: a casing having a base and a main cover secured to the base, the casing accommodating a circuit breaking mechanism; a recesses formed in one surface of the main cover, the opposite surface of which is on the side of the base, the recess being adapted to receive an auxiliary device of the circuit breaking mechanism; and an auxiliary cover mounted on the main cover in such a manner as to close the recess. The circuit breaker is automatically tripped when the auxiliary cover is opened, thus permitting installation of the auxiliary device thereon with high security.

Abstract: In a drawout type switch gear, rotation of the lead screw (7) is locked automatically at the connected position and the test position of the drawout/push-in unit (R), symbols or marks for representing these positions are provided on an indicator plate (18), which is driven laterally behind the front panel of the circuit breaker by a cam-rod type motion-direction transforming link (23, 19, 21, 18) and is arranged to be visible through display windows (15c) provided on the front panel (15). The insertion of the detachable handle (111) into a polygonal hole (7a) provided on the front end of the lead screw (7) is Inhibited by a blocking arm (110a), which is interlocked with a lock plate (16) driven by motion of the drawout/push-in unit (R).