Allen,

Wire must be sized for the expected load.

It should be fused to protect it and the connected equipment form
damaging current in the case of failure.

The cranking current of a 4-108 at shirtsleeve temperature is hard to
measure, but the peaks are around 500-600 ampere for 70-100 miliseconds
then dropping to 300-400 between peaks. If the fuse is in the cranking
circuit, I'm surprised it is still intact.

Stater motors are not very voltage sensitive. Most engines can crank on
a #2AWG wire and not have a problem.

Do not try to set up to crank from the house battery, just be sure that
the only load on the start battery is the engine. It is a waste of time
and effort and will only cause you problems.

This is what I do www.southpointechandler.com, in my area of the world.

If you want to discuss this more, I'm here alot.

Matt Colie


bushman wrote:
I am ready to install new batteries. I have not found a reference for wire
size - between - batteries. I have six T105 six volt batteries. What size
wire should be used to series and parallel them? The boat has 2/0 with a
250amp fuse running to the battery selector switch. I am not sure how much
my started draws (Perkins 4-108) but I would like to size to start from
either the starting or house batteries or both. One more thing that does not
look right is that the Neg wire on the starting battery is size one or two
connected to the house bank Neg only. Shouldn't there be a jumbo size wire
directly to the engine block at the starter?

Thanks as always. I couldn't have come this far without you folks.
- Allen