Wire Guage Size?

funideafunidea Registered Users Posts: 6
Im not sure if im going AC or DC yet. Please help me with DC and AC wire size calculations in my PV setup.

Minnesota temps
10 - Kyocerea 210 W panels (2100 watts)
Series
100 ft distance
Max Voltage 26.6V ea.
Max Current 7.9A ea.

Thanks forum!

Comments

  • JburgessJburgess Solar Expert Posts: 130 ✭✭✭
    Re: Wire Guage Size?

    I have situation similar to what you are wanting to do. My panels are on a out building 100 feet from the house. My installer recommended putting the inverter on the house and running DC in between. He said inverters are sensitive to voltage drop, and would require heavier wires to prevent it from going off line. Don’t know if that’s true or not. The out building is fed with 3/0 copper, but I was required to have a dedicated meter and disconnect for the solar by the house meter, so I couldn’t use it.

    Each of my strings has 15 KD210 in series. He chose to run #10 XHHW for each string.

    The voltage and current you quoted are the numbers for peak output. I believe the max voltage is 33.2 open and the bolted current is 8.58 A.

    Hope this helps.
  • BB.BB. Super Moderators, Administrators Posts: 32,648 admin
    Re: Wire Guage Size?

    Wire size and series/parallel array setup really depends on the GT inverter you will be installing.

    AC vs DC -- DC you may be able to run higher Vmp array voltage vs the 240 VAC from the AC panel--however, it probably will not make that much of a difference (if Vmp=2xVac, then you could go 3 wire gauges smalller--3 AWG = 2x or 1/2 change in wire cross section and roughly a 2x or 1/2 change in current capability).

    Another couple of questions... If you need heavy AC out near the shed--it may be worth bringing 240 VAC to the send.

    And, I have found that GT inverters (or any switching MPPT type charge controller) can make for some interference on radio bands (Broadcast AM band is very common for close range interference). Placing the Inverter away from your house/transceivers/etc.) may be a good idea (hard to know, every product is different, and sometimes the installation itself affect the noise problem too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • funideafunidea Registered Users Posts: 6
    Re: Wire Guage Size?

    no i dont need AC at the shed? Sorry can you dumb it down and suggest a wire gauge size?

    PVP 2500 Inverter.

    THanks
  • BB.BB. Super Moderators, Administrators Posts: 32,648 admin
    Re: Wire Guage Size?

    Using the PV String sizing tool, it look like you can place 10x 210 watt Kyocera panels into one series string.

    Isc (short circuit current for 210 watt panels) 8.58 amps for the DC string. x1.56 for NEC safety factor (1.25x for circuit rating, another 1.25 for NEC safety factor) (note, should be 1.56x Isc of panel:
    • 8.58 amp Isc * 1.56 = 13.4 amp minimum circuit (15 amp next standard size)
    Then use a wiring drop calculator like this one or pick another (this one uses Excel). Use 8 amps for Imp, 100' for 1/2 wiring length (two wires, 200' round trip). Use 14 awg for first calculation, use 277 volts single phase to calculate percentage drop (or you can do your own).

    From the calculator, we get ~1.8% drop--or ~5 volt drop. We aim for 3% loss maximum, and many people aim for 1%.

    Same calculation with 10 AWG: We get 0.7% drop or roughly 2 volts.

    I don't know much about the PV family of inverters, and I am not the Code Guy or a licensed electrician--but the above is a fairly conservative estimate of the minimum circuit requirements (15 amp, 14 awg) would be... And what a 10 awg run would do for you.

    Assuming you pull a permit and get utility approval for your installation, an electrician will do the final calculations and submit them with the permit application. Also, there are different types of insulation and amount of "conduit fill"--You would need an National Electric Code book (or equivalent for your location) to do all of the calculations and table look-ups to define the insulation type, etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solarvicsolarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: Wire Guage Size?

    PVP has a real nice string chart that could help you a lot. I checked it for maximum coldest of -30 f and you could put 12 panels on that inverter. Voltage 40.8 at -30f. For my fronuis inverter I have a string of Kyocera 158G. that operate at a close voltage similar to what 12 of the panels you have. I run the dc from combiner box 60 ft.to inverter mounted on garage with #8 and 240 ac from there 80 ft. to meter shut off box with #10 and I still get 240 ac to meter. I think the electrician should have run #8 on the 240 ac as I have 2 inverters feeding the 220 ac. I am still getting 240 with that size wires. S:Dlarvic
  • solarvicsolarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: Wire Guage Size?
    Jburgess wrote: »
    I have situation similar to what you are wanting to do. My panels are on a out building 100 feet from the house. My installer recommended putting the inverter on the house and running DC in between. He said inverters are sensitive to voltage drop, and would require heavier wires to prevent it from going off line. Don’t know if that’s true or not. The out building is fed with 3/0 copper, but I was required to have a dedicated meter and disconnect for the solar by the house meter, so I couldn’t use it.

    Each of my strings has 15 KD210 in series. He chose to run #10 XHHW for each string.

    The voltage and current you quoted are the numbers for peak output. I believe the max voltage is 33.2 open and the bolted current is 8.58 A.

    Hope this helps.
    I am using high voltage GT inverter at the garage and run 240 ac about 80 ft. to a disconnect at meter with no problems and get 240 volt. Passed inspection that way and power co approved.
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