Using mast to complete earth/negative circuit?

[skyflyer]

Whilst the mast is off the boat I have taken the opportunity to fit LED bulbs to the masthead tricolour and anchor lights. I am also fitting a new combination deck and steaming light. As all the cabling is looking a bit dodgy (corroded) I thought I'd replace that at the same time. To reduce the cable runs required is there any reason not to bond the steaming light earth (negative) to the mast and then make the negative connection from the masthead lights to the mast also? That way I can run a three core cable to the deck/steaming light and a twin core to the masthead, rather than using three core on both.

An alternative might be to use 5 core and cut into the insulation at the halfway point to loop three cores via the deck/steaming and then on up to the masthead, simply tying up the excess for the two unwanted wires at the half way point?

Or just run separate cables and be done with it - although space down compression post is tight with radar cable and transducer and VHF cable as well!

 

[nigelmercier]

Consider this.

My mast was grounded via the VHF antenna. The mast is bonded to the keel. The sail drive is meant to be isolated, when it became grounded due to a fault, it suffered bad corrosion.

 

[William_H]

Provided you can get a good long term connection to the mast at the lights and at the bottom I see no reason to be concerned with corrosion. Difficulty is that inevitably you will have copper wiring lugs under SS screws onto ali. Still Ok if you cover it with a grease to exclude moiusture.
Re 5 wire cable I can get some 5 wire made for trailer lights at a motor factor reasonably heavy wire but not tinned. good luck olewill

 

[prv]

I don't have any first-hand experience, but everything I've ever seen written about the idea of using the mast as return has been to say "don't do it".

I did mine a couple of years ago all in tinned two-core. One pair to the steaming light, one to the deck lights, one with supplies for tricolour and (separately) windvane light, and another with supply for the all-round-white and a common return for all three. Two flat thin-wall pairs are not significantly bulkier than a single round three-core, and if you've gone to LED then you will be able to reduce the cable size anyway (assuming it was wired correctly before).

Pete

 

[skyflyer]

I don't have any first-hand experience, but everything I've ever seen written about the idea of using the mast as return has been to say "don't do it".

I did mine a couple of years ago all in tinned two-core. One pair to the steaming light, one to the deck lights, one with supplies for tricolour and (separately) windvane light, and another with supply for the all-round-white and a common return for all three. Two flat thin-wall pairs are not significantly bulkier than a single round three-core, and if you've gone to LED then you will be able to reduce the cable size anyway (assuming it was wired correctly before).

Pete

I'm certainly attracted by the idea of tinned cables which you can't get in more than 3 core anyway. If I read your post correctly there were two twin cables going to the masthead with 3 feeds and one return, is that correct? As a matter of interest for a ~45ft mast what size of cabling would you suggest for LED - presumably the limiting factor is the common return which has to carry 3 loads?

 

[ghostlymoron]

This calculator will size the cable for you http://www.solar-wind.co.uk/cable-sizing-DC-cables.html however when using LEDs, it may be that the mechanical strength of the cable is more important than the current carrying capacity.

 

[rubbishman]

I'm certainly attracted by the idea of tinned cables which you can't get in more than 3 core anyway. If I read your post correctly there were two twin cables going to the masthead with 3 feeds and one return, is that correct? As a matter of interest for a ~45ft mast what size of cabling would you suggest for LED - presumably the limiting factor is the common return which has to carry 3 loads?

Anch
Ancor marine sell 5 core tinned.

 

[Chalker]

Don't do it. Use proper cablen.

When, not if, you get a bad joint and turn on a light, a) it will not work, b) the mast will be connected to +ve through the light.

Good recipe for corrosion.

 

[prv]

I'm certainly attracted by the idea of tinned cables which you can't get in more than 3 core anyway.

I only use tinned cable on board, but even if you save thruppence ha'penny by using plain copper below decks, I would definitely advocate tinned for the mast and other above-decks stuff. I have a five-core cable going to my nav light switch though, so more than three, tinned, is possible.

If I read your post correctly there were two twin cables going to the masthead with 3 feeds and one return, is that correct?

Correct.

As a matter of interest for a ~45ft mast what size of cabling would you suggest for LED

You should use one of the online calculators (or I have a spreadsheet which I put together from first principles), together with the rated consumption of whatever lights you have, to work it out. But I would guess it'll probably end up being 1.5mm².

Pete

 

[Chalker]

Don't do it.
When, not if, you get a bad connection the madt will connect to +ve through the light, good corrosion recipe.

The LED lights will take so little currect that you can almost certainly use twin 1.5mm to each bulb. Join the -ves together begore the deck plug/socket if used.

 

[nigelmercier]

The LED lights will take so little currect that you can almost certainly use twin 1.5mm to each bulb. Join the -ves together begore the deck plug/socket if used.

I'd be inclined to rate the cable as if you were using filament lamps, certainly in terms of current if not voltage drop. If not, carry spare LEDs.

 

[David2452]

you can't get in more than 3 core anyway.

Yes one can, I regularly use 5 core tinned and screened 1.5mm2 cable for LED mast work and other aplications, it is available in higher conductor numbers than 5 even.