Fairly long run from Inverter to AC Disconnect / Service.

I am planning out a 13 KW DC installation at my son’s rural acreage. It will be a roof mount on a new detached garage/storage shed about 200 feet from where the underground service / Main Terminal Box is located in the yard.

Because of the exposed / exterior location of the interconnection site in the yard, I wish to mount the Fronius V11.4-1 Inverter in that building and make the 200 ft run in 1 ½” pvc buried conduit. Probably will use #2 AWG THWN for the 2 hot wires and #6 AWG for the Neutral and GEC runs --- that seem about right? The max rated output current for this inverter at 240 V is 47.5 A AC but will normally be operating at a max of a little less.

Also, this inverter’s AC Terminals accept a max of #4 AWG wire, so what is the best way to transition from #1 or #2 AWG to #4. I don’t like wire nuts and pig tails with that much current so will probably use split bolt connectors --- I kind of remember that MiNite Solar had a neat connector for doing this, but can’t find it now.

I will also need to get power from this Main Terminal Box back to a Sub Panel in this new building. Any problem with running these feed wires in the same conduit with the inverter’s or should they be in a separate conduit?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Fairly long run from Inverter to AC Disconnect / Service.

    I think you're making it hard on yourself.

    Across 200' 240 Volts @ 50 Amps using 6 AWG gives a V-drop of 3.4%. I would not be worrying about trying to fit 4 AWG or larger.

    I know of no issue with running a set of wires from the inverter output in the same conduit as a set of wires carrying AC back to the building.
  • BrentBrent Solar Expert Posts: 64 ✭✭✭✭
    Re: Fairly long run from Inverter to AC Disconnect / Service.

    From what I remember the code allows one to include conductors from the SAME circuit in a conduit. You should not mix circuits, for example conductors from a PV systerm and a wind gen. in the same conduit. I believe that would also apply to feeder conductors and PV conductors in the same conduit.

    THWN is not rated for buried conduit as that is considered a wet location as THWN is listed as dry only. However if you use dual rated THWN/THWN-2 or THWN-2 then you should be ok.

    Brent
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Fairly long run from Inverter to AC Disconnect / Service.

    if for voltage drop reasons you still wish to opt to go #4 then you could use an electrical box with cover to tie the #4 wire to the #6 pigtails to run up to the inverter. not sure the best way to make the tie, but something like this could work,
    http://www.solar-electric.com/16220-2.html

    or even this,
    http://www.solar-electric.com/tbb.html

    edit to add-
    sorry i got the gauges messed up, but the options i linked still apply.
  • WallyWally Registered Users Posts: 11
    Re: Fairly long run from Inverter to AC Disconnect / Service.

    Good catch Brent --- didn’t write that correctly, the wire I am planning on is THHN/THWN-2.

    I probably could get by with #4AWG, but 500 ft of #2 AWG is $655 delivered and #4AWG $418, so only $237 more and with the 30% Fed Tax Credit a $166 difference.

    With close to 20,000 KWH’s output per year over 20 years would be 400, 000 KWH’s, so even a 2% less voltage / power drop could net 8,000 KWH’s at say an average of $0.20 / KWH over these 20 years and be about $1,600. Probably a little over optimistic, but definitely should have a reasonable payback.

    Actually, I was more concerned with the voltage drop causing tracking problems for the inverter with resulting dropouts. But I have this same inverter installed here, although on a very short run, and Xcel Energy has hit it with everything from 214V to over 270V and it has never dropped off. Probably more paranoid about this then I need to be.

    I just got to thinking about the #2 AWG wire size problem. It has a diameter of 0.378” with 19 strands.
    #4 AWG is 0.318” or only 0.060” less. Each of the 19 strands on the #2 wire must be about 0.020” so clip the ends of 3 of them off and I think the remaining 16 will easily fit directly into the AC connector.

    Probably the simplest and least loss way to do it.
  • BrentBrent Solar Expert Posts: 64 ✭✭✭✭
    Re: Fairly long run from Inverter to AC Disconnect / Service.

    Clip the three strands from the middle so the inspector won't catch it...LOL.
    They get pretty testy here if they find out someone did that.
    Brent
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