wire sizing confusion,

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zozomike
zozomike Solar Expert Posts: 134 ✭✭✭
Hi, I have 12 Shell/ Solar World 165 panels set at 45 degrees, with orientation true south. They are divided into 4 strings with a combiner feeding to a FX80, the run to controller is almost 80'. Summer FX80 readings are voltage mid day hovering around 110vdc, amps 20. Those seem to indicate a feed wire #8, I had #10 before but a backhoe (ahem, accident ) means 1'm upgrading again. My confusion is when I read the specs on the panel it says peak power current is 4.72A, times 12 that's 56 A, which would require a $#4 run? I must be misunderstanding the spec? I hope?
Thanks

Off grid, all solar, passive and active (winter wood heat supplements) PV DHW.

Array 1-- 12 Sunpower 250, Outback FM 100 3kw

Array 2-- 12 Sunpower 250, Outback FM 100 3kw

Well array 780w, 6 Kyocera 130 w with Grundfos sqflex 11 and cu200 to elevated storage, ( 2- 330 g tanks,) no battery storage at well

10 24 volt Battle Born Lithiums

Outback Flexpower Two, VFXR 3524A 7kw


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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
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    Re: wire sizing confusion,
    zozomike wrote: »
    Hi, I have 12 Shell/ Solar World 165 panels set at 45 degrees, with orientation true south. They are divided into 4 strings with a combiner feeding to a FX80, the run to controller is almost 80'. Summer FX80 readings are voltage mid day hovering around 110vdc, amps 20. Those seem to indicate a feed wire #8, I had #10 before but a backhoe (ahem, accident ) means 1'm upgrading again. My confusion is when I read the specs on the panel it says peak power current is 4.72A, times 12 that's 56 A, which would require a $#4 run? I must be misunderstanding the spec? I hope?
    Thanks

    Your max current from the array will be (1.25)(4)(Isc). You'll want to derate the conductors for continuous use/conditions of use and then size them up if you need to to get to whatever voltage drop is acceptable to you.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: wire sizing confusion,

    The Solarworld 165's Isc is 5.3 Amps. You've got four strings in parallel, so that's 21.2 for the whole array. Times the NEC derating is 26.5 Amps. The Voltage on three in series will be around 120 (103.2 Vmp, 129.9 Voc) so using the only V-drop calculator I can get to work on this netbook ... 80 foot run I get a result of 2.7 Volts drop using 8 AWG and that's less than 3% of the low Voltage figure, so that's what I'd pick.
  • zozomike
    zozomike Solar Expert Posts: 134 ✭✭✭
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    Re: wire sizing confusion,

    Ah, I was adding all the amps of each panel, I thought I was correct with #8 but having failed at this "simple " stuff too often wanted to check before digging another ditch. thanks

    Off grid, all solar, passive and active (winter wood heat supplements) PV DHW.

    Array 1-- 12 Sunpower 250, Outback FM 100 3kw

    Array 2-- 12 Sunpower 250, Outback FM 100 3kw

    Well array 780w, 6 Kyocera 130 w with Grundfos sqflex 11 and cu200 to elevated storage, ( 2- 330 g tanks,) no battery storage at well

    10 24 volt Battle Born Lithiums

    Outback Flexpower Two, VFXR 3524A 7kw