Wire Spec - Advice please!

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Wandering Star

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I want to rewire my deck level navigation lights which comprise separate port and starboard AquaSignal 40 units mounted either side of the pulpit with a ditto stern light mounted on the pushpit. The boat is 27 feet long (Vancouver 27) and the longest run of cable to the switch panel including routing it round various obstructions etc, will be about 28 feet.

What specification of wire should I purchase? I need to buy the wire by the weekend to take it out to Portugal on Monday. I want to buy the wire in UK to a good spec.

Thanks in advance.
 
I've just had my mast removed to replace the 11 year old standing rigging (in preparation for sale). While it was off the boat I decided to replace the steaming light with a combined steaming and deck light. I discovered that the wiring was already in place. It simply had domestic 3-core mains cable running up the mast. Both the lamp ends and the through-deck-cabin ends of the cable looked to be in good condition.
 
Assuming incandescent bulbs rather than LED, I've just run your numbers through an online volt-drop calculator and it thinks 1.5mm^2 will be ok. This surprises me slightly, so perhaps someone else can confirm.

You want tinned cable for this application, to prevent corrosion (I've never seen a nav-light cable in un-tinned copper that wasn't corroded, albeit usually still working).

Not sure what else there is to specify; I buy 100 metre reels of 1.5mm tinned cable from wherever I can find the cheapest price at the time (it does seem to fluctuate, I guess with copper prices) and have no complaints about the quality of any of it.

Pete
 
I've placed an order for a 30 meter reel of 1.5mm tinned 2 core cable with ALM Electrical Solutions (www.almsolutions.co.uk) who provided an amazingly quick response to my enquiry - about 5 minutes between me emailing them and getting their reply and placing my order. Quicker than driving to the shops to buy it! Total cost was £34 including next day delivery so good value too.

Thanks guys for the information and if its the wrong stuff, I know who to have kneecapped!

Cheers, Brian.
 
prv said:
Assuming incandescent bulbs rather than LED, I've just run your numbers through an online volt-drop calculator and it thinks 1.5mm^2 will be ok. This surprises me slightly, so perhaps someone else can confirm.

You want tinned cable for this application, to prevent corrosion (I've never seen a nav-light cable in un-tinned copper that wasn't corroded, albeit usually still working).

Not sure what else there is to specify; I buy 100 metre reels of 1.5mm tinned cable from wherever I can find the cheapest price at the time (it does seem to fluctuate, I guess with copper prices) and have no complaints about the quality of any of it.

Pete
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I don't think you need thicker from the electrical point of view. i might have gone for a bit thicker in the interests of mechanical strength, but I doubt that 1.5sqmm will be a problem.
 
Thre are various on line calculators as said.

I usually now calculate things for myself


If you have 2 X 25 watt bulbs at the bow then that's 50 watts ... call that 4 amps at 12 volts

The distance is 28 ft ... but thats 28 ft of positive and 28 ft of negative so 56 ft total........ call that 17 metres

Now the usual max allowed volts drop is 3% .... 3% of 12 volts is 0.36 volts

The resistance of the cable that will lead to 0.36 volts at 4 amps is 0.09 ohms

If 17 metres has a resistance of 0.09 ohms 1000 m will have a resistance of 1000 x 0.09/17 = 5.29 ohms

We are there fore looking for cable that has a resiatance of no more than 5.29 ohms per 1000 metres

Look at the table here http://www.engineeringtoolbox.com/wire-gauges-d_419.html and you will see that cable of 5.29 ohms/1000m is between AWG 12 ( 3.3mm²) and AWG 10 ( 5.26 mm²)

AWG 12 will there fore be just about adeqatete AWG 10 more than adequate by a good margin

However that is pretty heavy cable and you will probably be better off running two cables, one to each light.

Each needs to be only half the cross-sectional area so AWG 14 (2.0mm²) will be quite adequate


Rework the calculations for a single stern light....... Or if the distance is not too dissimilar use 2.0mm² cable for that as well


Use tinned cable to avoid future corrosion problems


Please check my maths.... I am having a "bad maths day"
 
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maby said:
I don't think you need thicker from the electrical point of view. i might have gone for a bit thicker in the interests of mechanical strength, but I doubt that 1.5sqmm will be a problem.
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Fair enough. Just that we get regular posts from people replacing cables in their mast, saying "this formula (or calculator) says I need 2.5mm cable up the mast - that can't be right, can it?" And we usually run the numbers and say "yep, that's what you need if you insist on putting a white-hot coil of wire up there. Fit LEDs instead." So I was mildly surprised that 1.5 is enough in this case.

I use 1.5mm wire for all general purpose wiring on my boat (complete rewire on the old one, increasingly large amounts being replaced piecemeal on the new) except for high-current things like autopilots, fridges, and bilge pumps. I'd consider it entirely adequate from a physical strength point of view - anything that would damage it would also damage the insulation on bigger stuff, so if that's a risk you'd use armoured or trunking anyway.

Pete
 
prv said:
I haven't actually checked, but I think a 27 foot boat can use 10 watt bulbs for sidelights. That's what I was assuming for my calculations, anyway.

Pete
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Aquasignal 40 lanterns are I think you will find supplied with 25 watt bulbs........... My new tricolor was.


You are right they can be replaced with 10 watt bulbs ( for vessels below 12 m IIRC) ... which are available to fit.... I had 10 watt in my old tricolour. ( I may have bought it with a 10 watt bulb??)

Depends what you want and how important highly visible nav lights are to you whether you keep the 25watt bulbs or reduce to 10 watts.

( PS I now have an LED tricolour equivalent to 25 watts)


Rework the calculations if using 10 watt bulbs!
 
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All these online calculators and tables have it arse about face and most calculations are the same, the way to do it is decide the voltage drop you can accept first. From there it is very simple and can be used for all conductor materials once the constant is known, copper being the material that most interests us.
Constant for copper is 10.75, ergo,
10.75 multiplied by Amps drawn multiplied by round trip in feet divided by allowable volt drop, this gives the circular mil area. Convert that to Mer Can wire gauge or mm2 and there you go.
 
David2452 said:
Constant for copper is 10.75, ergo,
10.75 multiplied by Amps drawn multiplied by round trip in feet divided by allowable volt drop, this gives the circular mil area. Convert that to Mer Can wire gauge or mm2 and there you go.
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That's a useful guide, but I can't get my head around the math at this time of night to find the equivalent metric contestant.
 
JSYmartini said:
Someone mentioned mechanical strength - the ABYC code states a minimum of 16AWG (1.3sqmm) for any run more than I think 8 or 12 inches.
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Indeed, but (from memory) that applies to single core cable not sheathed multi core, examples being N2K cable, 24AWG twisted pair shielded used in 0183 and other multi core sheathed power cables and approved manufacturer equipment looms. All that said I use minimum 1.5mm2 in everything except signal cables and N2K power supplies except on the rare occasions when I use thick N2K backbone which has 16AWG power supply cable but I have never used that on a leisure craft.
Are you thinking of CFR183425 which applies to petrol inboard craft?
 
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