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Grounding for AC system (with Microinverters)

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  • Grounding for AC system (with Microinverters)

    Is it sufficient to run your ground to the meter box, or is a dedicated new grounding rod required for the panels/racking?

    My design sheet (approved by elec company and city) doesn't really say anything about grounding rods, so I'm guessing that is only needed for DC installations?

    In any case... the design specifies ECG 12AWG. That can't be right, is it? I've always understood ground must be a heavier gauge than the line (which is 12 AWG). I see some other comments in this forum saying they use #8, others #10. Bare, solid, insulated?

  • #2
    I am not an electrician. Follow the advice of your power company, city, and/or a licensed electrician. With that said...

    If the power company and city don't ask for another ground rod, you don't need it. They are probably assuming that your existing house has a good ground rod.

    If you don't install a new ground rod, run your rack ground to the common ground inside your load center / main circuit breaker box. Don't do anything in the meter box. Don't connect ground to the NEUTRAL bus in the load center. Ground should be a separate bus.

    I believe that the ground wire must be at least as large as the other wires, so if they are 12, then ground can be 12.

    Some people insist on bare for ground, because that way, it can't be confused for anything else. Others like green insulated wire because insulation gives the wire some protection, and doesn't cost much more. It's your choice whether to use solid or stranded. Stranded is more flexible, and again doesn't cost much more. Stranded is a tiny bit harder to connect, but not enough to matter. Note: I am not familiar with the term ECG and haven't seen it used for ground leads.

    Lightning protection is a difficult subject. The more you do, the less likely you are to be damaged by lightning strikes near by. Adding another ground rod may help. Adding a lightning arrestor may help. Adding a lightning rod on the roof may help. Using fatter wire may help.

    If you're in a part of the country that gets a lot of lightning, you probably want to be very conservative, and do as much as possible. If lightning is rarely a problem, you may get by with less. If your house is hit by a direct strike of high-energy lightning, even with the best protection, it could burn to the ground. But the odds of that are super low. Odds of lightning hitting nearby are higher. It's all statistics and your risk tolerance.

    Even if lightning is not a big issue in your area, I think it is good practice to drive one new ground rod and run the racks directly to that new ground rod. Then run a wire from that same connection point on the new ground rod to your load center ground. I also think it is good practice to install a good lightning arrestor. These are both inexpensive and improve your odds of surviving lightning.
    7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV


    • #3
      Ok, so if I do run a new ground rod, it sounds like I ought to tie that all in with everything grounded (PV to junction box, and from there to new rod AND over to load center).

      BTW, I forgot to mention this is for grid-tie, stating the obvious at this point.