6mm cable or 4mm ?

Discussion in 'Solar Power' started by Ambilkate, Oct 16, 2015.

  1. Ambilkate

    Ambilkate Funster Life Member

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    What cable do you use 6mm or 4 mm does it matter when only doing a 6 to 8 meter run ?we are looking at putting 1x240 solar on van now but can't buy 6mm over the counter only 4mm we can purchase 6mm of ebay but trying to source all items locally and can only get 4 mm :( may have to give up and buy of eBay have all the links via funsters Thankyou but Kate doesn't like to buy over the net and trying to sorce everything today
    Bill
     
  2. scotjimland

    scotjimland Funster Life Member

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    Hi Bill

    yes.. it does matter ..in a low voltage application, the cable size is critical, not for the load.. but for the losses.

    the cable size is determined by the the length of run, wattage, and acceptable loss ..

    using the cable sizing tool, the theoretical correct size for that panel for a 6 - 8mt run, allowing for 3% loss, is 10mm

    4mm is too small.. and 6mm will just about do it.. the smaller the cable size the greater the volt drop = the less efficient your panel..
     
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  3. Gorse Hill

    Gorse Hill Funster

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    Depending on what you calcs are
    Screw fix do 10mm t&e and if using flex 6mm has a similar current carrying capacity , pretty sure B&Q do as well
    I would personally put in place the largest conductor allowing for further expansion
    Whats required and the cost involved on that length is minimal
     
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  4. Gromett

    Gromett Funster

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    I always recommend 6mm cable no matter how long the run or how little wattage you are putting on. It also reduces losses. In addition if you want to add additional panels in the future you won't need to upgrade the wiring.

    The cost difference between 4 and 6mm cable is negligible compared to the overall cost.

    I buy my 6, 16 and 25mm cable on ebay and it is very cost effective.

    Auto electricians will have the cables in stock but will be expensive.
     
    Last edited: Oct 16, 2015
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  5. Freespirit1

    Freespirit1 Funster

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    Hi Bill - just google "Industrial control Panel Manufacturers" in your area - one of those will have the right cable and colour you need - they will even crimp the correct lugs on for you too I expect while you wait.
     
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  6. Gromett

    Gromett Funster

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    PS: Remember when using calculators that the voltage at the solar panel side is higher so the current is lower. My panels from memory are about 17V I think. So 240W / 17V = 14Amps.
     
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  7. Theonlysue

    Theonlysue Funster Life Member

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    I don't think that their regulator will allow over 300w re panels.
     
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  8. scotjimland

    scotjimland Funster Life Member

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    that was the numbers I used

    Capture.PNG
     
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  9. Ambilkate

    Ambilkate Funster Life Member

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    Bills measuring up on the roof at the minute this is what is on the back of the panel we saw yesterday solar.jpg
     
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  10. Gromett

    Gromett Funster

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  11. Gromett

    Gromett Funster

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    That looks like a 48V panel. Make sure your regulator handles 48V in and 12V out. (I am sure you have already)
    AT 52V you would only need 1.5mm cable for 3% losses according to Jim's calculator and 4mm would give you 1% losses. I would still go for the 6mm cable however. Also please check the cable you use is rated at 50V+.
     
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  12. Gromett

    Gromett Funster

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  13. laird of Dunstan

    laird of Dunstan Funster Life Member

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    Those cable calculators are very helpful , I'd work out the run and have the cables cut to size ,don't use anything that will chew up the end of the cable when cutting, if you buy the lugs online make sure that they are the crimping type ,pop into your local control panel shop ,ask for the workshop and they guys will most likely crimp the ends for you ,its important that the correct tool is use to crimp as it will stamp a number at the same time as the crimp ,ask the guys in the panel shop to put on some heat shrink at the ends.
    I've built the odd control panel in my time ,it's best to use multi strand cable rated to the correct voltage, twin and earth is solid copper and is not suitable for your application :)
     
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  14. Ambilkate

    Ambilkate Funster Life Member

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    Thanks everyone back to the drawing board
     
  15. Freespirit1

    Freespirit1 Funster

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    Snap - all good advice there - and memories of Brand Rex Tri rated eh!
     
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  16. laird of Dunstan

    laird of Dunstan Funster Life Member

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    I started off as an apprentice electrical fitter on flameproof, explosion proof ,HV and LV switchgear , I've built untold numbers of control panels :D
    oh yes we know what tri rated cable looks like :D
     
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  17. Judge Mental

    Judge Mental Funster Deceased RIP

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    and I have installed them in another life(y)
     
  18. laird of Dunstan

    laird of Dunstan Funster Life Member

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    "Laughing" I'm looking at one right now with an old satchwell bms system ,been there to judge ,built them,installed them ,tested them ,commissioned the poxy things :)
     
  19. Judge Mental

    Judge Mental Funster Deceased RIP

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    I remember now!....your ones were Rubbish!lol Still have nightmares regards wrestling with monster armoured cables:)
     
  20. laird of Dunstan

    laird of Dunstan Funster Life Member

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    Oh yes :) bodgit and scarper control panels (y)
     
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