Navigation light wiring

[Fairwinds23]

I would be grateful for some advice: I have to replace the wiring at the pulpit of my starboard nav light which has worn through

The bulb is 25W and my boat runs on 12V

Am I right in thinking the current draw is 2.08 A and therefore 3A wiring is the correct replacement?

and

If I use wiring of a higher rating for the benefit of it being more robust what consequence will it have?

Many thanks

 

[tillergirl]

If I use wiring of a higher rating for the benefit of it being more robust what consequence will it have?

It will mean you reduce voltage drop which you need to do. You need to refer that current requirement to one of those clever tables that calculates voltage drop over the length of the cable from power source to light and back again. I one in a book here. What is your overall cable run?

 

[rob2]

Trouble with starting with only 12 weedy little volts is that they need all the help they can get just to reach the lightbulb! To this end, the larger the wiring you can fit the better as there will be less voltage drop.

Just don't be tempted to use solid wires (e.g. domestic mains) as it will suffer from work hardening and probably snap. In an application such as the nav lights, you are also fighting salt corrosion, so it may well be worthwhile to get tinned wire. If you don't , you'll find yourself pulling new wires through on a regular basis as the copper conductors turn black with the salt.

Rob.

 

[tillergirl]

To get only 3% drop in Voltage at the unit over a 60ft total distance you require 10AWG, for between 60-90ft, 8AWG - source Nigel Calder, Boatowners Mechanical and Electrical Manual. Agree with the tinned and multi-strand comment.

 

[Fairwinds23]

The distance I have to run is about 1m i.e. to the existing wiring under the deck which is in apparently good condition, into which I will splice replacement wiring to the pulpit

thank you for the advice about tinned wiring

Having looked up "AWG" - ohms are mentioned and I am now above my pay grade. However may I take it that 10AWG tinned wiring would be a good choice?

 

[tillergirl]

AWG is American Wire Gauge 10 is 5.27 in square mm or 2.59 in conductor diameter.

The answer to your question is yes, in my opinion, provided what you are splicing it to is the right cross section and being in mind that each 'splice' on a bateau is a source of extra resistance and potential failure.

 

[dt4134]

The distance I have to run is about 1m i.e. to the existing wiring under the deck which is in apparently good condition, into which I will splice replacement wiring to the pulpit

thank you for the advice about tinned wiring

Having looked up "AWG" - ohms are mentioned and I am now above my pay grade. However may I take it that 10AWG tinned wiring would be a good choice?

10AWG is 6mm^2, which I suspect is significantly thicker than what you have at the moment. 3% voltage drop at 12.6V is 0.38V but remember TillerGirl gave you figures for a 60M run. Presumably you are over 12M loa, but I'm guessing your bow light wiring isn't 60M there and back. From what you say, you're replacing 1M whilst the rest of the run is unchanged, so going over the top for that 1M will have negligible effect on the overall voltage drop.

I'd also look at LED bulbs to reduce the current, but that's another thread (well actually maybe even a hundred other threads if you do a search).

Anyway, here's one source for tinned wire.

http://www.seascrew.com/browse.cfm?MARINE-CABLE--TINNED-&l=0000000197

Where you join the wires make sure you use a butt connector with heatshrink to keep the damp out.

 

[tillergirl]

They are figures for 60 FEET! Not metres.

 

[Fairwinds23]

Many thanks that is very helpful

 

[dt4134]

They are figures for 60 FEET! Not metres.

OK, but it is still a lot more than the metre he's replacing. The resistance of the wire is measured in mOhms per metre.

Look at this table of resistance for stranded wire.

http://www.stealth316.com/2-wire-resistance.htm

10AWG is 0.0033 Ohms per metre, so the voltage drop for a metre of wiring at the 2.08A quoted is 0.00686 Volts

14AWG (~2mm^2 and more readily available) is 0.00845 Ohms per metre which gives a voltage drop of 0.0176V per metre.

In the grand scheme of things the difference is negligible.


For the OP, the formula is simple V=IR, R is the resistance per metre multiplied by the length in metres, I is the current, which multiplied by R gives the voltage drop in Volts.

The link also allows you to do the calculations in feet. In fact it has a calculator to do them for you.

 

[Bodach na mara]

Firstly, it would help if we knew roughly what type of boat you are working on and what age it is. You may not be aware that the builders of boats sometimes do not install wiring that is up to the job. On my Westerly of 1975 vintage most of the wiring is in domestic flexible cable and while the "5 amp rating" may be fine for a 240 volt system, there are large voltage drops due to the higher currents in the 12 volt system. You may be only using a short run to below deck, but the wire from the battery to that point may be no better than the one you are renewing and may be seriously undersized.

I also have a stern light mounted with a cable in the pushpit and it was wired with figure-of-eight "bell wire". When that gave up I could not get a thick enough wire through the tube and resorted to clipping a cable down the outside and running a new cable to a point below deck to connect to. I do not like this arrangement and am looking for a better way to do it. One solution is to go down the LED route and use "3 amp flat twin flex" for the short run from light to below deck. At least I can get that into the tube I think

 

[Fairwinds23]

Firstly, it would help if we knew roughly what type of boat you are working on and what age it is"

It's a Beneteau 423 from 2005, my original post could have been expressed better

How "thick" a wire can I run to the nav light at the pulpit to give the maximum resilience without affecting the electrics.

 

[prv]

How "thick" a wire can I run to the nav light at the pulpit to give the maximum resilience without affecting the electrics.

You can go as thick as you like, or rather, as thick as you can fit through the holes and round the bends. Wires that are too thin cause problems from an electrical point of view, there's no such thing as too thick.

For what it's worth, I'd probably pull some off my leftover reel of tinned 2.5mm^2 if I was doing that job.

Pete

 

[CAPTAIN FANTASTIC]

Why are you using 25watts bulb?; the new generation of LEDs are so much better in terms of durability, brightness and low energy (1 ~ 2 watts)

 

[VicS]

It's a Beneteau 423 from 2005, my original post could have been expressed better

How "thick" a wire can I run to the nav light at the pulpit to give the maximum resilience without affecting the electrics.

There is no problem, other than that of physical size, in using heavier cable.

If it is TOO THIN you will suffer volts drop.

For a distance of only 1m 3 amp (0.5mm²) will be adequate from an electrical pont of view but for physical robustness I would use something heavier. 0.75mm² (6amp) at least, preferably 1.0mm²


.