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Old 23 January 2012, 22:35   #1
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Re wire which cable size?

Hi there I'm wanting to rewire my nav lights and was thinking of using a twin core cable from the switch to the A frame.

Is 1.0mm 16 amp ok, too big , too small, or would 11amp 0.5 be fine??

I'm not really up to speed on cables.

Any help would be great.

regards Richard
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Old 24 January 2012, 02:56   #2
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I would go with 1mm mainly for the strength of the cable as you drag it down cable ducts etc.
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Old 24 January 2012, 03:02   #3
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Quote:
Originally Posted by richardjawilson View Post
Hi there I'm wanting to rewire my nav lights and was thinking of using a twin core cable from the switch to the A frame.

Is 1.0mm 16 amp ok, too big , too small, or would 11amp 0.5 be fine??

I'm not really up to speed on cables.

Any help would be great.

regards Richard
Richard,
Firstly, not sure where your current ratings come from, they seem a little over optimistic to me.
I do not know what current rating your nav lights are, mine are 10W, so I will take that in absence of anything better. Taking the worst case, that is you are wiring the red and green in series, you will be drawing the current for both lights. If both are 10W, voltage is 12V, and VI=W (V, voltage, I, current, W, wattage), I =20/12, or slightly less than 2amps. Sounds OK, but volt drop down the cable run is usually the major issue for our sort of applications. Assuming a 10 metre length (out and back) your volt drop will be something like 1V. So I would definately not go any smaller than 1mm cable. If you went to 2mm cable your volt drop will be of the order of 0.2V. From memory standard size widely available is 2.5 mm; I would try to find some of that.
Sorry to come over all chalk dust, I do a little bit of this in the day job. If I have been over pessimistic in any of these calculations, apologies, let me know.
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Old 24 January 2012, 03:37   #4
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I used twin core 25 amp cable for my tri navigation lights, probably a little ott but works great.
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Old 24 January 2012, 03:45   #5
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Oh, and for marine applications it is best to try to use fully tinned copper wire to minimise the dreaded black copper - salt water corrosion
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Old 24 January 2012, 04:10   #6
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I just did my lights on my SR4 & used 1mm 16.5amp works so far!
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Old 24 January 2012, 08:07   #7
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Remember to wire the white light onto a separate circuit to the red/green, so it can be used as an anchor light.
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Old 24 January 2012, 09:15   #8
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Ok fine. Good points re tinned wire and voltage drops.

Thanks
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Old 24 January 2012, 09:15   #9
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It depends upon how long you want your connections to last ...

a) What will the current be (i.e. 3x10w bulbs will be 30/12=2.5A) ?

b) To size the wire given the current and length I use a standard table like the one here Wire Gauge Tables

So for example a 25 foot run from the switch in the console to the light I would pick 16AWG from the table - so using the top table 1mm sq cable will be fine

c) The online calculator here Stealth 316 - Wire Resistance and Voltage Drop Calculator allows you to enter the lenth and voltage to work out the voltage drop for each wire size - so over 25ft you would drop 0.25v using 16G wire which for lighting would usually be fine, although you could go up a size if you want to reduce the voltage drop.

d) I would suggest only using marine tinned copper cable - otherwise after a few months/ years the copper will turn black after exposure to sea air/water and you may well have to do it all again ...
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Old 26 January 2012, 10:09   #10
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Tinned is the only way to go, not the cheapest, but you can buy it by the metre from here... Tinned Copper Thin Wall Cable
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Old 26 January 2012, 12:54   #11
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Quote:
Originally Posted by Ian M View Post
. Taking the worst case, that is you are wiring the red and green in series, .
Series?

Surely you want to wire them in parallel otherwise they only get 6volts each?
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Old 26 January 2012, 13:22   #12
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excuse me if this is a silly question but i take it then that the red and green lights should be on 1 switch and the white on a separate switch.
should you not have all three on when running at night.
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Old 26 January 2012, 17:15   #13
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excuse me if this is a silly question but i take it then that the red and green lights should be on 1 switch and the white on a separate switch.
should you not have all three on when running at night.
Yes you should, but if you are at anchor, you only want your all round white, not your steaming lights. Hence the separate switching arrangement. Carling do a switch that has the facility for "steaming" or "Anchor"
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Old 26 January 2012, 18:57   #14
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thanks Dave so if stationary at anchor white lights only

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Yes you should, but if you are at anchor, you only want your all round white, not your steaming lights. Hence the separate switching arrangement. Carling do a switch that has the facility for "steaming" or "Anchor"
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Old 27 January 2012, 02:56   #15
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thanks Dave so if stationary at anchor white lights only
Yup, & it should be an allround white, not a stern white. There are also rules for how high above the steaming lights it should be, but these are often ignored on small boats due to difficulty obtaining the correct separation distances.
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Old 27 January 2012, 03:44   #16
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Carling do a switch that has the facility for "steaming" or "Anchor"
Any switch that is double pole/double throw, on/off/on will do the job.
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Old 27 January 2012, 04:58   #17
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Or just have 2 on/off switches
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Old 27 January 2012, 05:10   #18
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Any switch that is double pole/double throw, on/off/on will do the job.
Yup That's what the Carling switch is, I didn't want to get too technical.
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Old 27 January 2012, 07:53   #19
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would prefer and have, to have two switches, since middle position means they could get knocked to on position!

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