Battery cable size for earth?

it would make sense to me to have both battery cables
the same size , otherwise the weakest link in the system would be the smaller earth cable ,
cheers mechpete

The Earth return carries the same current as the live side so should be the same size, with a good quality connector with lots of surface area at both ends. If your setup allows both batteries to feed a cct simultaneously then tieing both earths together is also a good idea.

It's good practice to have very heavy cables on both live and earth sides to minimise voltage drop. I'd need to see the schematic of your setup to offer more specific advice but live and earths should have at least 12mm diameter of copper conductor.

BTW never believe the amp rating on jumper leads as they are typically overated by 3 times or more.

Gazza

thanks for this informtion

Matt,
Have a look at how much room there is to run cables that size from your primary battery down and around to your secondary battery, plus the mechanical protection required.

I choose a different way and ran 16 sq mm cable back to my secondary battery via a dc dc charger and on to the rear anderson plug.

If I have to jump start, which I hope I don't have to do. I have a set of jumper leads I made using 50 sq mm welding cable.

G'day Matthew G3

I have done exactly the same project in my current model BT50 with a second battery in the canopy.

The cable I have is not marked with gauge, and I cannot recall what I bought. Measuring it up, it is either 0 or 00 - when I calculate the sq mm the result is between the two in Narva's on-line catalogue. Given likely measuring error, I think it is probably 0 gauge, both pos and neg. I ran the neg to the factory chassis earth point near the battery.

I have tested it as both jump start and winch assist and it works fine. It's a long cable run, so IMO it's worth the expense of the heavy cable, especially for sustained loads like winch assist. I used a 300 amp forklift fuse at each end of the positive. Under a heavy winch load I measured a bit under 200 amps in the circuit.

Cheers