Hi
@Dorothea, I thought I'd chime in here since that's our MRBF listing that you linked to;
@MisterSandals has it correct, though - for your application, you should have a 250A fuse if you're running a 12v nominal system. These MRBFs are perfectly appropriate for that. Please bear in mind, though, that the main purpose of the fuse is to protect the
cable connecting the inverter to the batteries, not the inverter itself, so as long as you're using appropriate cable gauge for the length of your run you're good with the 250A MRBF. If, for one reason or another, you need to under-size your cabling then you should also under-size your fuse so that the cable stays protected at all times.
For instance (still assuming a 12v nominal system voltage): if your inverter is 4' or less away from your battery bank (so 8' round-trip), you
should be using 1AWG or heavier to safely carry the maximum current rating of the inverter that distance while maintaining less than 3% voltage drop. In that case, a 250A MRBF (or Bussman ANL or breaker) is perfectly appropriate. But now let's say that for some reason you can only possibly use 4AWG cable... you shouldn't, and I hope you won't, but for the sake of argument let's say that you absolutely
need to use 4AWG, you positively
cannot go to a heavier gauge than that. Well, in that case, you would want to put a 150A fuse on the circuit, because the maximum continuous current rating of an 8' round-trip length of 4AWG wire is 150A... so you want the fuse to blow before your cable insulation starts to melt, if that makes sense.