36 volt array wire size question...

OrioN
OrioN Registered Users Posts: 13 ✭
in PV Installers Forum - NEC, Wiring, Installation #1
Mornings...

I cannot seem to locate a wire size calculator for 36v, all I find are 12/24/48.

My 2 arrays are 36v. The furthest one will have a 'to & back' wire length of 24'.
I want 3% drop of less. The total watts for a single are 585w.

Any one able to size this up?

Thanks!
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Comments

  • KeithWHare
    KeithWHare Solar Expert Posts: 140 ✭✭✭
    #2
    Re: 36 volt array wire size question...

    Using the "Any Voltage Voltage Drop Calculator" calculator at http://www.electrician2.com/calculators/vd_calculator.html with 36 Volts, 16.25 Amps, and 12 Feet one-way, a 10 AWG wire will give you a 1.33% voltage drop.

    Keith
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  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    #3
    Re: 36 volt array wire size question...
    OrioN wrote: »
    The total watts for a single are 585w.


    Thanks!

    I can't tell what you mean. Is this 585w total power, or is that for one of the two arrays?
    Do the arrays share the same wire or are you using two separate runs?

    Assuming they are on separate runs, and that 585w is just for the array with the longer run....let's see you're probably looking at around 11 amps of current, so

    With only 24 feet of wire, AWG 14 will give you less than 1V (3%) drop, but I think the NEC requires a minimum of AWG 12.

    Personally I'd go with at least AWG 10, it will only cost a few pennies more with that short a run.
    That will give you about 0.3V drop or less than 1%.
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  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    #4
    Re: 36 volt array wire size question...
    KeithWHare wrote: »
    Using the "Any Voltage Voltage Drop Calculator" calculator at http://www.electrician2.com/calculators/vd_calculator.html with 36 Volts, 16.25 Amps, and 12 Feet one-way, a 10 AWG wire will give you a 1.33% voltage drop.

    Keith

    Unless he's running a MPPT controller located out at the panels, the Isc of a (nominal 36v) 585w array will probably be less than 12 amps.

    I'm guessing he's using 3 ea 195 Watt panels with an Imp of somewhere around 10.7 Amps.

    Just sayin is all ;)
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  • OrioN
    OrioN Registered Users Posts: 13 ✭
    #5
    Re: 36 volt array wire size question...
    Peter_V wrote: »
    I can't tell what you mean. Is this 585w total power, or is that for one of the two arrays?
    Do the arrays share the same wire or are you using two separate runs?

    Assuming they are on separate runs, and that 585w is just for the array with the longer run....let's see you're probably looking at around 11 amps of current, so

    With only 24 feet of wire, AWG 14 will give you less than 1V (3%) drop, but I think the NEC requires a minimum of AWG 12.

    Personally I'd go with at least AWG 10, it will only cost a few pennies more with that short a run.
    That will give you about 0.3V drop or less than 1%.

    The 585watts are for one array (36v) with a wire 'loop' length of 24ft. The second array is 20ft. Both arrays with then meet at my combiner and tie in parallel for total array voltage of 36v. (Morningstar MPPT 60)
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  • OrioN
    OrioN Registered Users Posts: 13 ✭
    #6
    Re: 36 volt array wire size question...

    Looks like 22 AWG wire it is...

    Thanks all!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #7
    Re: 36 volt array wire size question...
    OrioN wrote: »
    Looks like 22 AWG wire it is...

    22 awg? :confused:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • OrioN
    OrioN Registered Users Posts: 13 ✭
    #8
    Re: 36 volt array wire size question...

    Who wants to be the first to spank me?

    Ok... I cramped.

    The total watts for one array is 285w, (not 585).
    The array voltage is 36v.
    The wire loop from the combiner to array and back is 24ft.

    So... what is a good wire size for minimal loss?

    Thanks!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #9
    Re: 36 volt array wire size question...

    Using a generic voltage drop calculator:
    • 285 watts / 36 volts =7.9 amps
    • 24' round trip / 2 = 12' one way run
    • 36 volts * 3% = 1.08 volt maximum recommended drop
    • 36 volts * 1% = 0.36 volt really low voltage drop
    • 12' run, 7.9 amp, 16 awg => 0.93 volt drop
    • 12' run, 7.9 amp, 12 awg => 0.36 volt drop
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • OrioN
    OrioN Registered Users Posts: 13 ✭
    #10
    Re: 36 volt array wire size question...
    BB. wrote: »
    Using a generic voltage drop calculator:
    • 285 watts / 36 volts =7.9 amps
    • 24' round trip / 2 = 12' one way run
    • 36 volts * 3% = 1.08 volt maximum recommended drop
    • 36 volts * 1% = 0.36 volt really low voltage drop
    • 12' run, 7.9 amp, 16 awg => 0.93 volt drop
    • 12' run, 7.9 amp, 12 awg => 0.36 volt drop
    -Bill

    That didn't hurt at all!

    So... I have this nice roll of Ancor 14-2 AWG marine that I've used to wire up some stuff in the RV build, with a good 50+ feet left. Perfect!

    Thanks!


    PS... in a short while, I'll post pictures/videos of my Sprinter with the 2 arrays (40"x60", 285watts each) which automatically tilt via electric actuators (Lenco Marine Trim Tab).
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #11
    Re: 36 volt array wire size question...

    Just watch that the cable is UV resistant or you shade it from the sun.

    Have fun!
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • OrioN
    OrioN Registered Users Posts: 13 ✭
    #12
    Re: 36 volt array wire size question...
    BB. wrote: »
    Just watch that the cable is UV resistant or you shade it from the sun.

    Have fun!
    -Bill

    I park under big trees all the time...
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #13
    Re: 36 volt array wire size question...
    OrioN wrote: »
    I park under big trees all the time...

    Even a tiny shadow on a solar panel can cut its output to near nothing. Dappled sunlight from being under a tree will make your solar panels pretty much useless.

    UV will deteriorate normal romex insulation.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #14
    Re: 36 volt array wire size question...

    Me thinks OrioN is having a bit of fun my saying to "shade" the wires (keep them under the panels) and OrioN saying to shade the panels under trees.

    In any case, I am not sure shading is a good substitute for UV resistant wiring.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #15
    Re: 36 volt array wire size question...
    BB. wrote: »
    Me thinks OrioN is having a bit of fun my saying to "shade" the wires (keep them under the panels) and OrioN saying to shade the panels under trees.

    -Bill

    Yea, I thought so too...but just in case he might have actually been serious...figured I'd admonish. :)
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