[Mr V]

Both the main breaker and the breakers used on the PDB are thermal breakers. Once they heat up to a certain point they will trip. Due to their sealed plastic cases they will trip sooner if they are put back into service before they can fully cool. However tripping a few times does not cause them to trip sooner the next time if they are allowed to cool to room temp. Now if they have tripped dozens or hundreds of times they may become fatigued and trip easier.