What is the difference between and aux contact, alarm switch and overcurrent trip switch in a circuit breaker?
Molded case circuit breakers
Powerpact B, H, J, L, M, P and R frame circuit breakers
Auxiliary Swiches (OF) change state when the breaker changes from the open to closed or closed to open condition. Type "A" contacts are open when the breaker is open and closed when the breaker is closed. Type "B" contacts are open when the breaker is closed and closed when the breaker is open.
Alarm Switches (SD) change state only when the breaker trips for any reason
. The SD works off the mechanism and when the mechanism trips, it operates. The SD is reset when the mechanism is reset.
Overcurrent Trip Switches (SDE) change state only when the breaker trips due to an overcurrent
. For example, using a shunt or undervoltage accessory to trip the breaker does NOT
change the state of an SDE switch. The SDE is reset when the breaker is reset.