The Natural Philosopher wrote:
Jules Richardson wrote:
On Tue, 14 Sep 2010 15:12:50 +0100, tinnews wrote:
I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

No, it's steel hull. What sort of accident/problem are you thinking of
when you say "accidental ground path back to the battery". Surely I'm
protecting against just that, the chance of one of those big, heavy
wires shorting to the hull/superstructure - which can't happen on a
wooden/plastic boat.

Mostly misreading on my part, I think :-)

I just think of a metal hull as a nice chunky ground (similar to the
chassis in a car), and of motors etc. as having their metal cases
connected to ground too. Say the mounts for two of those motors wear or
are installed incorrectly, you may end up with the two motor cases linked
via the hull - something that could go unnoticed for a long time. A
positive-side fuse would protect Motor 1, but a ground-side wouldn't
because the motor would still have a ground path back to the battery via
the hull and Motor 2.

It takes a couple of faults for it to happen, but I've seen that kind of
thing done due to botched installations, manufacturing faults, or age-
related wear. As for why it's relevant in your case? It's probably
not ;-) I only realised later that you were talking about having a ground
disconnect very close to the battery - and so long as there's no way that
the -ve terminal of the battery could find a path to the hull, it's a non-
issue...

cheers

Jules

This may be of interest.

http://www.electricalcarservices.com...es-p-1383.html

If you want a safety cutoff that will handle hundreds of amps.

That's just a switch, it's not difficult to buy battery isolation
switches to do the same and they don't cost more than £200 like the
one above! I can see good reasons for using something like the one
above in motorsport and similar applications but it really isn't that
necessary on a boat as long as you have a readily accessible
mechanical switch.

--
Chris Green