Boat wiring - polarity?

[catlotion]

something I've been meaning to look into...

We've only had the boat (Beneteau Oceanis 350) for a year and when I fitted some new instruments I noticed that the polarity seems to be reversed. Prob wouldn't have noticed but the Raymarine instrument wouldn't work until we switched the power leads over.

The battery leads are connected correctly, so not sure where the reversal is coming from - can anyone think why this would be? The boat has been mucked about with quite a lot in the past by previous owners so expecting to reveal some bodge job somewhere...

I did look behind the main breaker panel last year and I think it was reversed there as well. Suppose it could be that the isolator switches have been wired this way. It was re-engined with a Volvo MD2020 - is it possible this change was made then?

confused...

 

[prv]

Positive earth? Nothing should be earthed in the way that a car is - you should have two wires. Do you mean that the black wires are positive and the red wires negative?

Sounds like quite a cockup somewhere!

Pete

 

[catlotion]

sorry, yes. Just reversed. Didn't mean positive earth at all... (think I need some lunch...)

 

[davidej]

Even more confused!!

Have your lunch then explain exactly what's your problem.

 

[catlotion]

ah, had some food now.

it's just that all original wiring in the boat is black wire positive, red wire negative. Including the breaker panel...

 

[davidej]

I would suggest that it is very unusual - but now you know, what difference does it make?

After all +ve = red and -ve = black is only a convention and now you know your boat has a different one you should be OK.

I think you should stick with it - it would be even more confusing if, when wiriing in new gismos, you went back to the normal convention.

 

[nigelmercier]

all original wiring in the boat is black wire positive, red wire negative. Including the breaker panel...

Are you sure? The breaker is often in the negative.

 

[Elemental]

Are you sure? The breaker is often in the negative.

Is that right? I know there's no 'ground' for things to short to, but what would be the rationale behind putting the breaker on the -ve ?

 

[whipper_snapper]

Is that right? I know there's no 'ground' for things to short to, but what would be the rationale behind putting the breaker on the -ve ?

It is not common but there is no inherent difference between the safety of protecting pos vs neg with breakers.


But it all sounds very strange. I would just get a meter, put its pos probe on battery pos and roam over the boat, breakers etc with the other lead looking for a voltage. You should fairly quickly be able to work out what is happening.

 

[VicS]

It was re-engined with a Volvo MD2020 - is it possible this change was made then?

The colours for the engine and its control panel are black for negative and red for positive!

 

[catlotion]

yes, it is strange. Everything works fine though. It just makes me feel a bit dirty when I add something new and sometimes have to wire the red to black and black to red.

I'm a bit puzzled as to why the instrument wouldn't work when wired up correctly - would there be a diode or something in there?

apologies for increasingly confusing and vague thread!

 

[Bosun Higgs]

Could be any of a number of reasons from French workmanship through to a bodge or simply that the guy doing some wiring had not got enough wire of the right colour. Several bits of my boat wiring are the wrong colour and I'm the culprit

Key thing is that you do any wiring up work using a digi meter to check first. You should have one on the boat anyway.

 

[catlotion]

yep - always got my trusty multimeter to hand

It's all the original Beneteau wiring as far as I can tell, not newly added...

 

[Phoenix of Hamble]

the polarity/colour must reverse somewhere in the system if the batteries are correctly attached.... i'd personally HAVE to trace it back to find that point, as it would bug the hell out of me!

 

[davidej]

I think it unlikely that the boat was originally wired that way.

If you trace back to the battery and find where it has been reversed and put it back to normal, you then have to trace everything else which will need reversing. Obviously it doesn't make any difference for lights but you will have to be sure that every other item (there might be up to 50) is checked and reversed where necessary.

I would be inclined to live with it

 

[Gordonmc]

A long shot, but could the boat have been wired for the US market?
The reason I ask is my US built boat came with the DC two core wiring with black + and white -.
The AC wiring was the same; white -.
During the rebuild I stripped everything out and made black - and white + which is closer to the (to me) expected way of doing stuff.
I guess the wayb of confirming how the OP's system operates is to find out whether red or black wires go to a common bus.

 

[catlotion]

mmm - possibly. I can't remember for sure whether it was black and red or black and white tbh (it was this time last year when I replaced the instruments and my memory is rubbish - although I think I would have remembered black/white combo).

The boat was registered in Corsica originally...

I'll prob just leave alone - doesn't matter for most things (lighting, etc) but will just have to remember when installiing any new electronics in the future...

Thanks for all the help everyone!

 

[prv]

mmm - possibly. I can't remember for sure whether it was black and red or black and white tbh

Oh!

If you'd said originally that it was black and white, not black and red, then I'd straight away have said that it was to the US colour code. Their ABYC rules have a fairly detailed set of wire colours (for signal wires as well as power) and 12v power is black and white as Gordon says.

Pete

 

[Spyro]

Positive earth? Nothing should be earthed in the way that a car is - you should have two wires. Do you mean that the black wires are positive and the red wires negative?

Sounds like quite a cockup somewhere!

Pete

I would have said on a boat the -ve is earthed through the engine block and an earth strap or through the prop shaft to the briney. On a car you don't have an earth just the body of the car which is referred to as the earth.

 

[Spyro]

Check out you switch/fuse panel there should be a bus bar that is -ve do you have a large conductor coming from the battery to that? What colour and what polarity is it?