I like to "fuse" at just above whatever current will usually be running thru the wire. A 75a charger, thru 2awg, means I would use a 90-100a c.b. I figure, this way, if the battery shorts, the c.b will (hopefully) blow long before the 2awg wire melts and catches fire, and voltage drop (thru c.b) will not be too outrageous. I've been running 45a thru a 50a c.b, and will be going bigger, as I don't like the v.d. I'm seeing at 45a.
Same goes for solar controller output. If normally less than say 25a to bank, thru 6awg, I'd use a 30a c.b. Using the same 30a c.b. before the solar controller's input has shown zero v.d., to two decimal places, at 8a input.
