Jay see 1997 GU build up

[Ben-e-boy]

Shorted to earth. I think we are talking in circles. If you have a main cable feeding a sub board, protect the feed cable as suggested with the 60 amp breaker, and the accessories off that board are protected by their correctly sized breaker or fuse per circuit The main breaker should be sized to protect the cable and the accumulated maximum load it might see if every accessory was drawing their maximum current. ie, if you blow a fuse on a circuit with a 5amp draw, the main breaker of 60a is not going to trip. If you damage the main feed cable between the battery and the sub panel,and it feeds to earth, the main cable breaker will trip.

Not in circles yet. I'm probably not explaining my point regarding fault current and instantaneous trips properly.