Vacuum contactor retrofit of a low-voltage power circuit breaker

Due to a misapplication of low-voltage power circuit breakers on high-cycling motor-starting services, the electrically operated mechanisms failed due to the large number of spring-charging, closing and opening cycles. Various options for correcting the problem were evaluated, and a vacuum contactor retrofit of the circuit breaker was selected for some of them. The vacuum starter units are electrically and mechanically interchangeable with the power circuit breakers. The paper discusses the design considerations and operating differences resulting from the technology conversion. It also discusses the differences in rating, function, and application