The invention relates to a mechanism for opening and closing a circuit breaker having an operating rod for moving the contacts of the circuit breaker between an open position and a closed position, which mechanism comprises: a frame; a first axle rotatably arranged in the frame; a cam arranged on the first axle, which cam is arranged to operate the operating rod of the circuit breaker; a first gear arranged on the first axle to drive the cam; a second axle arranged rotatably in the frame and parallel to the first axle; a sector gear arranged on the second axle, wherein the sector gear has at least one toothed sector and at least one toothless sector, wherein the at least one toothed sector engages the first gear upon rotation of the second axle; spring means for rotatably urging the sector gear; and locking means for locking the rotation of the second axle.