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Wire size for a solar panel?

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islander
Master Marine Consultant

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USA
4023 Posts

Initially Posted - 12/31/2009 : 11:11:08

So one of my winter projects is to install a 10 watt panel on the cockpit rail. The wire will run from the panel along the top rail down the upright and enter the boat through the transom using the same hole as the engine charge wire is. From there it runs a straight line to the battery compartment under the starboard settee. I only have a single 90amp battery that is fine for me. I would guess this line to be about 10-15 feet long. My question is what Gage/size wire would I use?

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

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Happy D
Admiral

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921 Posts

Response Posted - 12/31/2009 : 11:20:22

Here ya go.
Remember that it is round trip, so 15 feet is really 30 ft of wire.

http://bluesea.com/viewresource/535

Edited by - Happy D on 12/31/2009 11:26:03

islander
Master Marine Consultant

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USA
4023 Posts

Response Posted - 12/31/2009 : 12:26:28

Ok The panel puts out only .56 amp max. This chart only goes to 16 gage wire. Using the calculations from this chart it puts the wire size smaller than 16 gage on a 30ft run at 3% drop ???

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frog0911
Master Marine Consultant

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USA
1349 Posts

Response Posted - 12/31/2009 : 13:01:33

You could go to 18 gauge if you like, but I never use any wire smaller than 14 gauge on my boat electrics. On engine start from battery I use 8 gauge even though the run is only 8 feet. There is a lot of amp draw on start, especially if the engine is cold. I use the chart only as a guide to let me know when the wire I plan to use would be to small.

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Voyager
Master Marine Consultant

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USA
5368 Posts

Response Posted - 12/31/2009 : 17:33:31

Stranded wire is preferred over solid wire. Marine wire has lots of thin strands, while industrial wire (like THHN) uses fewer, heavier strands.

The former provides wire that is more flexible and conforms better to tight spots and short radii of curvature. The latter is stiffer and harder to work with.

The strands of marine wire are tinned or plated to protect them from the elements, whereas industrial wire is not. That's why it's justified to pay the extra money for marine grade.

Don Casey recommends that 16 AWG wire is the minimum size to be used on a boat, due to the presence of constant vibration.

18 AWG may provide the ampacity you need @ 1/2 an Amp, but is too light (in Don Casey's opinion).

Always best to use crimp connectors instead of "wire nut" type connectors on a boat. Shrink tubing will cover the crimp connections to extend their useful life a few more years.

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 12/31/2009 : 18:47:17

Concur with all the prior advice. I also haven't put anything smaller than 14 gauge marine wire on SL. I recommend finding yourself a ratcheting crimper, they make a much better crimp than a pliers type standard crimper.

Are you going to put a regulator on your panel?

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islander
Master Marine Consultant

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USA
4023 Posts

Response Posted - 12/31/2009 : 19:13:28

Yes I have a charge regulator, My thought was to have the smallest gage for aesthetic reasons being that the duplex wire will be strapped to the railing but I agree that going too small would be prone to breaking. The charge regulator has 16 gage wire pig tails so I will probably go with that size and according to the wire selection chart, 16 gage is still overkill for this application. This will be Marine grade wire only, I wouldn't use anything else.

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Happy D
Admiral

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921 Posts

Response Posted - 12/31/2009 : 19:40:20

I miss read the OP. I saw 10 amps, not 10 watts. Sorry, had my head in the clouds.
Been doin the amps thing all week.

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 12/31/2009 : 21:05:27

If you're going to run the wire along the railing, you might consider finding some long shrink tubing to give yourself another wear layer. My local electronics place stocks it in 4', 6', & 8' sections. I used it to waterproof my GPS power/data cable as well as my start/stop switches cable runs to my Power Tiller. It's not horribly expensive, and I figure it gives me substantially more protection in high wear situations. On the GPS cable, I did a double layer, but didn't bother on the switch cable run. The GPS cable gets moved around, stepped & sat on all the time, where the switch cable is pretty much out of the way.

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.