Mast Nav Lights - What wiring cables?

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Babylon

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Mast is down. Intend to spend this weekend fitting a new tricolour and anchor light, also check and revamp steaming light and deck-illumination unit (and also install new VHF antenna and cable).

So it seems sensible to renew existing wiring (don't know age and condition of old cables). Mast is a Selden unit with a relatively small internal conduit for all electrical cabling and co-ax).

What cabling should I use? Should I run separate 2-core cables for each unit, or think about multi-core?

Given that the bulbs are 10w and 25w (and 20w halogen for the deck light), do I need 0.5mm, 0.75mm or 1.0mm? Is voltage drop an issue with the smaller guage?

Thanks
 
General purpose article attached which might be of use:

Who Stole My Volts?

Ted Osborn

One of the lessons from the Ouzo tragedy was the point, strongly made by the Marine Accident Investigation Branch, that yacht tricolour lights can be very difficult to see. If you only show a tricolour light at night when sailing you might be almost invisible.

With this in mind, when my mast was down to replace rigging I looked closely at my tricolour. 15 years old, the lenses were clouded badly. UV light had caused them to degrade and it was no longer giving out the amount of light it was designed to. With that MAIB report in mind, action was called for.

Replacement lenses were not available, even from the manufacturer: I had to buy a new light. Research produced a choice of branded replacements: Hella, Aquasignal and Lalizas, plus several which were unmarked and anonymous and didn’t claim to meet IMO regulations and were clearly to be avoided. Joining that list, but perhaps only for the moment, are LED navigation lamps. These offer the brightness required by the regulations but seem not to cover the vertical angles to cope with heeling and maybe don’t have consistent 360 degree coverage. As far as I could find out none are yet approved by any maritime safety agency.

At least one manufacturer is now marketing replacement tricolour bulbs in the form of a plug-in LED unit that looks a bit like a pineapple. If the angle-of-coverage problem can be solved this may eventually be the way to go. But for now a traditional branded tricolour was my answer

While checking the condition of my tricolour I measured the voltages on the circuit. At the battery there was 12.8 volts – very healthy. At the foot of the mast there was only 11.9 volts, almost a volt had gone missing. This showed that the wiring from the battery through the tricolour switch and to the mast was in poor condition. But there was worse to come: at the top of the mast the tricolour terminals themselves were getting only 10.7 volts. Another 1.2 volts was being lost in the mast. However good the battery and lamp, the wiring was preventing nearly 17% of the power from reaching the top of the mast. The wiring had to be changed as well.

There is one major cause of this: copper wire and connectors exposed to salty air. How often do you see unprotected deck connectors totally uncovered when a mast is down for the winter? How often do you see exposed deck connectors when the wire can so easily be led through the deck and the connection made at a proper junction box just inside? How often do you see bare screwed connections instead of proper sealed efforts? Did you know that corroding moisture can wick its entire way up the mast inside the insulation in only five years?

Lamp bulbs are very sensitive to changes in the supply voltage: light output falls proportionately to the 3.4th power of the voltage. This means that a loss of only 5% in voltage reduces the light given out by about 20%. The light will appear to be ‘on’ but it is nowhere near as bright as it should be. In my case, losing 17% of my volts was cutting down brightness by over 50%, even before the degraded lenses did their bit.

If you are checking your own tricolour circuit – and I hope you are – don’t forget that you must have the light on and working. You are looking for the voltage drop which occurs under load. No load means no voltage drop so ‘open circuit’ measurement is pointless. Use an ordinary digital voltmeter.

My mast is 35 ft tall and there is 20 ft between it and the battery, via a couple of connectors and switches. Thus 110 ft of wire is needed to give the flow and return circuit required.

Lloyds and the American Bureau of Shipping give advice on selecting the right wire to use. Firstly, it must be ‘marine quality’ wire. The insulation must be UV resistant and the copper must be protected from atmospheric salt corrosion. The wire itself has to be ‘tinned’ to prevent wicking of salt and the terminations at switch and wire should be sealed. It must be strong and flexible enough to withstand the constant movement and vibration within the mast. Domestic cable bought from a DIY shop or motor-parts supplier won’t do.

Whatever the wire, it always presents a resistance to current passing along it and this determines voltage drop. Too much resistance means too much voltage drop. The thicker the wire, the less the resistance - so always choose a thicker wire if given the choice.

To calculate the size of wire you need to know the electrical load or power that the lamp will draw (probably 25 watts) and convert this by Ohms law to amps of current. The length of wire from battery to mast head is also needed and this must be doubled since the current has to flow back to the battery to complete the circuit. The permissible voltage drop has to be decided as well. At this point, your eyes may begin to glaze over. Not a problem if you’re a member of the Cruising Association – we’ll happily send you an Excel spread sheet which lets you work out what size of wiring you need. If you’re not a member of the CA (and if not, why not!) then you’ll have to fall back on specification charts given by wiring suppliers and do you own sums.

In my case the total permitted resistance in the wiring is 0.24 ohms. Only once I get past 3 mm² wire am I OK, since with this can go up to 129 ft without creating too much resistance. Effectively, though 2.5mm² would cause a total voltage drop of .6V, so I could decide to go down one size and still retain almost all of my tricolour’s brightness – the choice might depend on what tinned wire is in stock when I place my order.

If you sail at night, this is not a job to ignore, and it can even be tackled mast-up if you’re happy aloft. The consequence of not being seen by shipping is not a pleasant alternative.

(ends)
 
Did my 15m mast about a year ago I used 2.5 mm2 cable for all lights. My tri-colour / anchor only has a single return so that was 2 red and one black. All others a set of 2 cables for all separate lights
 
Very good post! To summarise then, if I want to do a proper job:
* use marine grade tinned wire;
* use deck-glands with sealed junction boxes inside the coachroof (not deck-connectors);
* calculate the min guage to use based on twice the distance from the light-unit to the switch-board, allowing for a 25watt tricolour bulb (less for 10watt anchor and steaming lights).

Off now to Google suppliers of marine-grade tinned wire (with sizing charts).
 
Voltage drop is the issue!

On THIS WEB PAGE there is a wire size calculator that you can use to size the cables,

Although the site is about solar panels the calculator is equally relevant to your needs.

It is set to 3% voltage drop, which is the normal figure used but you can change it if you want.

There is another HERE but your currents will be lower than those in the table.

The second of the above also has a link to a conversion chart from AWG to other wire sizing units eg mm² if required

(note the two links calculate the cable run length differently one takes the simple distance from end to end, the second requires you to double that to give a "there and back" figure)

You do not say what the cable run length will be so cannot advise on size any further, you will have to use the calculator to determine it.

Assuming 12 volts I would take take a 10 watt bulb as 1 amp and 20 or 25 watt bulb as 2 amps.

Three core flex will be right for a combined tricolour and anchor light unit. Twin flex for a separate steaming light or three core for a combined steaming and deck light.

You should consider using tinned (marine) cable rather than plain untinned domestic stuff.
 
VicS

Thanks for the link to calculator (I assume figure in distance box doesn't need to be doubled!)

12v system, assuming 3% voltage drop:

9m mast plus say 4m to switch-panel = 13m total for tricolour/anchor => 3 sq mm for 25w tricolour; => 1.5 sq mm for 10w anchor

About 10m total run (lower down mast) for steaming/deck lights (both 10w bulbs) => 1 sq mm

Just spoken to bloke at Merlin Powerstore: suggested for tricolour 3 sq mm (12AWG) as per calculation above. Alternatively, he suggested a single 12AWG Return (black) and separate Supply wires (red) at 18AWG 0.8mm

... at which point I developed the sort of nervous tic I remember having during physics A level classes! - so I think I'll just go with your suggestion for three strand to each combination unit: 3mm to the tri/anchor, 1mm to the steaming/deck.

Cheers

Babylon
 
<<<three core for a combined steaming and deck light>>>

If you were ever in the situation that both the steaming light and deck light were on at the same time, the earth return would be carrying the current of both together, which could overload it. For this reason I always try to remember never to turn both on at the same time.
 
I would add that for anything out in the elements (which mast wiring effectively is) it is infinitely preferable to have rubber sheathed cable rather than PVC. It is fully waterproof and will remain flexible. PVC is generally OK below decks but above decks rubber is the canine testes.
 
For serious 12V use - I advocate Trailer cable .... if it can survive being dragged around in the open come rain or shine - it can survive a boat. If you need multiple cores - it can be bought with various number of cores ... 6 .. 8 ... 9 whatever.

For mast lights ... I sadly admit that I use domestic mains cable two core - with separate cable for each light.

For through deck - I got fed-up with the plugs / sockets failing through green corrosion. So I removed the inserts and used screw connectors inside the bodies. So this gives me replaceable connection, it's above deck so mast off / on is easy, all I need is a squirt of silicon when I screw together to g'tee watertight. Cable is easily obtained ... can be replaced easily when mast down (which for me is every winter so longevity of cable life is not so vital)
 
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(I assume figure in distance box doesn't need to be doubled!)

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Correct, see "step 3" in the notes that follow!

Agree with your calculations.

Vyv's point about having deck and steaming light on together won't be a real problem IMHO. It wont overload the cable as such 'cos the cable is already well oversize from the current carying point of view. (1.0mm² will safely carry 10amps) You'll get a bit more volts drop but with both lights on maybe that wont matter.

If you take up Refuellers suggestion re trailer cable check the X sectional area. I have either found it not specified or too small but only checked a couple of sources. Using doubled cores is an option I suppose but might just as well use three core in the first place. Trailer cable probably is not tinned but I dont expect Refueller is either.
 
Actually what is supplied for "trailer cable" is simply rubber sheathed multi-core. Because it has stop lights, indicators etc it usually has at least 5 cores and because the distance is not great the cross section of each core is not big enough.
Go to an electrical wholesaler, not a retailer preferably and look at what he has available as tinned multi-strand copper with a waterproof (usually nitrile rubber) sheath. It's going to be more expensive but will last a lifetime. Untinned will corrode quickly, but tinned in a non waterproof sheath will too over time.
 
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Trailer cable probably is not tinned but I dont expect Refueller is either.

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Trailer cable probably is not tinned but I dont expect Refueller is either.

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No worries as long as I can get Tin open !! I hate it when the ring breaks of. /forums/images/graemlins/laugh.gif

Back to trailer cable ... I've used some pretty heavy gauge stuff in past when wiring caravan - certainly heavier gauge than usual "halfords" utility trailer stuff for lighting boards. One boat in past - I used it for distributing 12V around the cabin as I could colour code each item for separates.
 
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