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Thread: wire size?

  1. #1

    Default wire size?

    I apologize up front if this question has already been posted: I don't have the time to read through any more posting.
    I am running three 30v 200 watt panels in series, and I need to know if I need to size the wire running to my controller
    according to the 7 amps that each panel produces or a total of 21 amps?
    thanks, Brad

  2. #2

    Default Re: wire size?

    If they are in series the volts add and the amps are constant.

    If the panels are 200 watt STC and are 30 Vmp they should be around 6.6 amps Imp. The Isc should be around 7.26.

    One string of three in series would be 90 Vmp and 6.6 amps Imp. Then you apply the rest of the "normal" wire ampacity factors (number of conductors in a raceway, ambient tempuratures, etc). This will insure your wiring will efficiently carry the PV output.

    Then you also need to make sure your wire and overcurrent protection devices are designed for the maximum PV circuit current: Isc x 1.56. (+/- 11.33 amps)

  3. #3

    Default Re: wire size?

    If they are in series, you do not have a total of 21 amps, you have a total of 7 amps.
    Northern Arizona Wind & Sun Forum & Website Administrator

  4. #4
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
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    Default Re: wire size?

    I am a little confused... Is this a PWM controller or MPPT type. And what is the array wiring (series or parallel), plus what is the battery bank voltage and AH rating.

    Also, how far from the solar array to the Charge Controller/Battery installation.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  5. #5

    Default Re: wire size?

    Quote Originally Posted by BB. View Post
    I am a little confused... Is this a PWM controller or MPPT type. And what is the array wiring (series or parallel), plus what is the battery bank voltage and AH rating.

    Also, how far from the solar array to the Charge Controller/Battery installation.

    -Bill
    It is an MPPT controller, wiring is in series, battery voltage is 12v, array is approximately 18 ft away.

  6. #6

    Default Re: wire size?

    I intend to run 10/2 w/ ground outdoor rated wire. Any suggestions?

  7. #7
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    21,363

    Default Re: wire size?

    Using a generic Voltage Drop Calculator. Call it 7 amps at 3x30=Vmp-array=90 volts @ 18 feet. We usually use around 1-3% voltage drop maximum:

    • 90 volts * 1% = 0.9 volt drop (minimum cost effective drop)
    • 90 volts * 3% = 2.7 volt drop (maximum recommended drop)
    • 14 awg; 7 amps; 18 feet (one way distances) => 0.8 volt drop
    • 18 awg; 7 amps; 18 feet => 1.9 volt drop
    • 10 awg; 7 amps; 18 feet => 0.3 volt drop


    So, 10 awg is more than heavy enough for your application. Make sure your "outside" wire is UV rated (many are "wet rated" for burial and/or conduit.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

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