High amperage molded case circuit breakers are required to interrupt large values of current extended through a plurality of downstream breakers to respective loads. Problems of course arise both from the blade and contact mass required to carry the large current values and the forces required for their movement to properly close the contacts and the forces required to open the contacts and created on interruption of the current, including shocks to which the breakers are subject.
Generally a two link toggle assembly is erected to close the contacts and a latch holds the assembly erect against spring pressure when the knee or pivot between the toggle links is moved just past an aligned or over center position, as for example shown in U.S. Pat. No. 4,219,713. The force for disengaging the latch from the toggle is usually quite high and a long latch is therefore used or some other scheme creating a mechanical advantage is provided for minimizing the force required for releasing the latch which is proportional to the distance to which the knee is moved over center. These arrangements are expensive and calibration remains a problem in controlling the forces on the latch and the tripping distance through which the latch is moved to trip the breaker. In addition high amperage breakers are subject to substantial shocks, which may tend to release the latch resulting in inadvertent or undesirable tripping of the breaker.
In smaller breakers, contact blade pivots are electrically bypassed by a braided copper pigtail, however, in high amperage breakers this is not possible as the large size of the pigtail required to carry the current values reduces their flexibility. A pivot assembly which can carry the heavy currents and also pivotally support the cantilevered blades from the pivot is therefore desirable, but difficult to provide economically.
USPTO Backgrounds
USPTO Backgrounds