- Fails to open: The breaker does not open the circuit when commanded manually or by automatic signal or by protective device. The failure cause probably could be inadequate lubrication of the trip latch or trip mechanism, control circuit failure, open and shorted coil,mechanism linkage failure between operating mechanism and interrupters,trip latch surface wear,deteriorated bearings, deformation of trip latch flat surfaces, or external circuit failure including wiring and battery
- Opens but fails to interrupt circuit: The breaker opens but is unable to interrupt the current and/or open contacts. For vacuum type breakers, the cause cold be loss of vacuum in the vacuum bottle. For stored energy type breakers, the cause could be failure of arc chutes, puffer failure, or mechanical failure. For SF6 breakers, it may be low gas pressure or density. In the case of when the breaker fails to maintain the required dielectric isolation of contacts after opening operation, the failure cause could be the voltage exceeds the circuitbreaker capability, lightning, loss of gas pressure, loss of vacuum, or the mechanism did not travel complete distance.
Pic show a vacuum circuit breaker failure because loss of vacuum