This thread deserves to be hijacked, so I will speak of fuses.
My current work van setup has 1) 150 amp fuse at the starting battery positive cable that runs 20 ft to another 150 amp fuse that connects to the battery isolator, that then goes to 2 house batteries.
My 110v system is fed buy a generator with a 10 ga cord coming out of a 30 amp twist lock outlet that goes to a power selector switch. My shore power is 100 ft of 10 ga 20 amp cord that goes to the same power selector switch, my inverter is a 2000 watt 20 amp gfi protected with a 20 amp cord running back to same power selector switch.
From the switch 10 ga wire feeds a mini panel with 2 30 amp breakers that feed 6 circuits 3 of which are 15 amps and 3 are 20 amps.
1 of the 20 amps feeds a roof top ac. The others are there for machine use.
All lighting is 12v LED.
I only run 1 thing at a time as I don't have 4 arms. The roof top air will draw 13 amps max, more like 11, and is wired only to run on shore power and gen power. TV, all lights small fans are 12v, computer phones etc are all 12v charged.
Heat comes from propane camper furnace in wall.
Wiring from starting battery to house batteries is all 2 ga stranded welding cable. Wiring to inverter is 2 ga tinned marine stranded cable 3ft runs. 12 outlets are stranded 12/3 wire with 15 amp inside outlets & 20 amp GFI outside outlets.
There is another 100 ft roll out cord system used as extension cord to supply power from van.
This all works perfectly fine and I have even run other vans with 50 amp (not 150 amp) fused 12v systems between the starting and house batteries and never popped a fuse.
If my generator is 30 amp output, and my shore power can only be plugged into someone's house outlets (15-20 amp max) and my inverter is rated 20 amps, then I think I'm fused correctly. Even my boat that can plug into a 50 amp shore power at a dock is only 50 amp fused (110v) panel breaker.
So I might be missing the need for 400 amp breakers but it sounds like putting penny's in screw in fuses at grandma's house or you might just as well not fuse anything and depend on the power sources protection to protect itself.
My gen has 30 & 20 amp breakers, shore power is protected at the house or business I plug into by 15 or 20amp breakers, and inverter is protected with 20 amp gfi and low/high voltage breakers along with over heat breakers.
400 amp breakers / fuses sounds useless, my goal is to reduce my breakers /fuses down down down to their minimums, most of my small 12v stuff like cabinet lights etc are running on 5amp fuses.
Comments good or bad always welcome.