What is the function of auxiliary and alarm switches for molded case circuit breakers?
What is the function of an auxiliary switch for molded case circuit breakers?
Auxiliary (OF) switches open or close 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 .
SD or Alarm contacts change state only when the breaker trips (for any reason). They work off the mechanism and when the mechanism trips, they operate. The are reset when the mechanism is reset.
SDE or Overcurrent Trip Switch contacts change state only when the breaker trips due to an overcurrent. They are reset when the breaker is reset.