Earthing on boats

davew wrote:
> Hi,
>
> A friend that's just boaugh a canal boat is 'doing' it up and is
> worried about the
> electrics and has heard that boats use positive earth so he's asked
> me for advice.
> I know about electronics & house wiring (well a bit anyway) but have
> never considered this on a boat where he'd like to have a computer TV
> etc....
>
> Now considering I was going to help him sort the electrics out what
> else should I know that's differant from 'Land' electrics I tried
> searching for a helpful
> UK website but none found.
>
> Any pointers
>
> thanks

Usually, a boat has no "earth return", so the engine and electrics need a
separate connection to the battery negative. The usual system is to have a
distribution panel on which the positive is on the switch, indicator-lights
and fuse (or contact-breaker) side, and all the negatives are fed back to a
negative bus bar whic is connected to battery negative. The main switch is
usually positioned close to the battery or batteries, and if a 2-battery
system is used, a blocking diode is used so that the domestic battery can
run down to almost zero, whilst you still have a full battery for starting
the engine.

If you can get hold of a copy of "The 12-volt Doctor's Handbook", this is a
great starting point. Also Reading University's website used to have some
great stuff on marine electrics, but I don't know if this is still the case.


Dennis.