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 from the forces required to move the blade and contact mass used to carry the high current values and to provide control of the toggle assembly used for closing and opening the contacts in the event the breaker is tripped. These problems are compounded in high amperage molded case breakers since the size of the apparatus, while large, is substantially reduced from that provided in iron clad or open frame breakers of similar current carrying capacity.
A large closing spring is generally used in high amperage breakers to store energy for erecting the toggle assembly to close the contacts in the event the breaker is tripped and electrical power lost. Typical arrangements for charging a closing spring are shown in U.S. Pat. Nos. 3,289,790; 4,095,676; 4,167,988; 4,114,005; 4,166,205; 4,245,140 and 4,251,702 for example.
The use of a ratchet and pawl for tensing the closing spring such as shown in aforementioned U.S. Pat. No. 4,167,988 appears to offer mechanical advantages over other arrangements. However, the ratchet arrangement is subject to some short comings, since both manual and electrical operation with safety are necessary and control of the spring tension and electrical circuit are difficult to coordinate with economy, while allowing the spring to rotate the ratchet on discharge in the same direction, as when charging, creates problems.
Also opening the contacts of a high amperage molded case circuit breaker under high fault currents creates problems since the blade movement must be stopped within a relatively short distance despite the large mass and if stopped suddenly may create rebound. Rebound of the blades may result in momentary reclosure of the contacts and consequent additional deleterious arcing. An arrangement for stopping the blades with a shock absorber, which is engaged by the blade carrier crossbar, is illustrated in U.S. Pat. No. 4,267,419 and in U.S. Pat. No. 4,263,492 an arrangement for preventing contact reclosure or bounce is shown, however improvement in the effectiveness of these arrangements is desirable.