Alternator ground

Nov 16, 2012
1,052
Catalina 310, 2000, #31 31 Santa Cruz
Those of you who have upgraded your boat wiring: if you ran a new hot wire from the alternator to an ACR (or similar) did you also add a ground wire from the alternator to the engine or negative busbar? If so, what size wire, what size was the stud on the alternator, and where did you ground it?

I did that when I rewired our Catalina 27, and was thinking it made sense to do the same thing on the C310, rather than rely on the mounting bracket to complete the circuit. Luckily the C310 already has large enough wire in most places, so mostly I only need to put new (quality) lugs on the ends of the existing cables; the C27 needed new cable almost everywhere. I'm following Maine Sail's advice on boat wiring, including rewiring the 1/2/Both battery switch; makes so much sense to me.
 
Feb 6, 1998
11,675
Canadian Sailcraft 36T Casco Bay, ME
Rob,

The case of the alt is ground/neg so any clean spot will work fine. This engine suffered from severe voltage drop in both the positive and negative sides of the circuit with negative being the worst. I cleaned the alt mounting ear to bare clean aluminum then ran a 6GA wire direct to, and stacked on top of, the clean & new 2/0 Battery cable lug on the engine. After this change nearly 90% of the alternator current was flowing though the 6GA wire, not through the rusty block. Neg wire should be same size as positive.