Under hood fuse panel wire fuse size?

[DAR00GAR00]

So I started working on my big 3 upgrade..... The way I’m doing it, I’m eliminating the factory fuse that the alternator wire and the under hood fuse panel is hooked to. I’ll be upgrading the alternator wire and fusing that on it’s on. Then fusing the wire going to the fuse panel also. The wire going to the fuse panel looks to be 8 gauge, but the fuse that was hooked to is 175 amps. I’m confused as to why there’s a 175 amp fuse on an 8 gauge wire.

What size fuse should I run solely for the 8 gauge wire going to the fuse panel?

 

[DAR00GAR00]

Anybody got anything?

Here’s the start while I’m waiting on my wire and everything else to come in the mail...
You can see I have a voltmeter/fuse above the firewall; this will be leading to the battery isolator and then to another voltmeter/fuse and then terminate at the 2nd battery. So each battery will be fused and I’ll be able to see the voltage of each separate battery at anytime.

Then I have the 2 inline fuses on the left of the battery. I planned on running the charging lead from the alternator to one of those fuses and then to the battery. Then the other one I was gonna run a lead from the battery through the fuse and then to the under hood fuse box. I’m just stumped on why there’s a 175 amp fuse on such a small 8 gauge wire and I’m not sure what I should do with it at this point.