Abstract: A vacuum circuit breaker includes a main frame and a vacuum bulb unit supported on the rear side of the main frame. The vacuum bulb unit includes an intermediate support unit disposed at a rear side of the main frame, and a pair of vertically aligned vacuum bulbs supported on the upper and lower sides of the intermediate support unit. Each of the vacuum bulbs have therein a stationary contact and a movable contact which is movably supported by the intermediate support unit. An insulator bracket has one end secured to the rear of the main frame and extends rearward to support the intermediate support unit at the other end. The insulator bracket has a substantially inverted U-shaped cross section. A pair of frame-shaped insulation mounting members are secured to the upper and lower sides of the intermediate support unit.

Abstract: A vacuum circuit breaker comprises a base, a support frame and an insulating frame. The insulating frame has a plurality of housing portions juxtaposed and separated from one another. These housing portions are made of plastics as a unit. The insulating frame is supported by the support frame which is detachably mounted on the base. The vacuum circuit breaker has a plurality of vacuum valves each having a fixed and a movable electrode, and plural sets of main circuit conductors. Each vacuum valve and each set of the main circuit conductors are provided in each housing portion. The vacuum circuit breaker has a operating mechanism moving the movable electrode of the vacuum valve, and the operating mechanism is supported by the support frame.