it cant be the arc that trips the breaker, if you do have an arc protection relay on your breaker then you need to check
the status of your arc prot relay and also check your settings on your o/c and e/f protection relay there is a
possibility that your setting are too low on the relay.
from my understanding of breaker fail and how it works it is there to protect the feeder in the event of a fault that occurs to that specific feeder and a protection relay does trip but the breaker fails to trip and the relay sends the signal to the incomer then the incomer should trip to...