Modern Trends of Low-Voltage Air Circuit Breakers

The history of low-voltage air circuit breakers has paralleled the development of power distribution. The desire for improved contacts led from an automatic knife-switch type of circuit breaker to an air circuit breaker equipped with a laminated copper brush. The trend from d-c systems to polyphase a-c systems led from the ``nontrip free´´ type of air circuit breaker to the ``trip free´´ breaker; and now the requirements for low maintenance, safety of operation, increased continuity of service, together with the trend to steel enclosing of switchboards and individual devices, is being met by new air circuit breakers equipped with solid silver main contacts, alloy arcing tips, and a new type of arc interrupter herein described.