Alternator Positive Wire Sizing

[Pelorus32]

G'day Gurus,

This may have been covered somewhere but I've searched and can't find it.

I'm rewiring the charging system on our boat. It currently uses an old Victron diode system to separate the batteries. The house battery never sees more than 13.2V on charge and of course you can guess what happens to the house battery. It's only 120AH but our needs are very modest.

I'm replacing the Victron with a CTek D250S Dual and a SmartPass. I already have them to hand and I've seen them doing a good job elsewhere...so that's not the question

The boat is powered by a 3GM30 with the standard 55A alternator.

The sparky who wired the boat took the positive feed from the alternator across the boat for about 6 feet to a shunt, using 10 AWG wire. From the other side of the shunt it goes to the live side of the starting battery switch again using 10 AWG for about 2 feet. This is instead of a short run from the alternator to the battery +ve on the starter according to the Yanmar wiring diagram.

Unless I'm mistaken all charging current is travelling over that 10 AWG wire for a considerable distance.

I reckon that wire is much, much too small for the job at hand. For various reasons the location of the shunt is probably the best compromise. So what I intend to do is to beef up that wire substantially. Am I missing something here and is that 10 AWG wire enough or am I right in wanting to upsize it and if so what size would you recommend - I'd rather be over than under in size.

All battery cables (to the switches and to the starter etc) are bigger than 2 AWG - I would guess 0 AWG and I have made up all leads for the new interconnects using 2 AWG...except for the lead from the alternator.

I'd appreciate views on sizing please.

Also if anyone knows the size of that +ve stud on the standard Yanmar alternator I'd be grateful. I'm away from the boat during the week and forgot to check.