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A few grounding questions

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  • A few grounding questions

    Hi ,
    I’m installing a ground mount solar system with multiple strings. I’m running DC from the multiple strings a long distance to the house where I will put the inverters. I have a few grounding questions and I haven’t been able to get exact answers with a lot of reading:

    1. I think I can combine the bare copper grounding wire from my racking and panels into one bare copper wire that will run the distance in my PVC conduit with the DC wires and connect to the two inverters. Is that OK to do? Note that I have a grounding rod buried at the arrays and will also connect to this.

    2. I have a bunch of excess bare copper wire. Can I use this for my AC output that will tie into my main house panel, or does it need to be insulated ground wire? I’m using flexible aluminum conduit between the inverters and the main house panel.


  • #2
    I am not an electrician, so your safest bet is to verify this with an electrician or your local inspector (AHJ). But that said...

    I think it is fine to combine all earth grounding in one wire, including the ground rod, poles, rack, and panel frames. But don't combine DC negative or AC common to this run. It is for protection and for lightning current, not for operating current.

    In my application, I found it impractical to run this through conduit. This is because I used stranded bare copper wire, and couldn't find a sealing cable gland that works with stranded bare wire. Instead, on the advice of an electrician, I ran it outside the conduit, attached to the conduit with cable ties. If you use solid wire for this ground, you may be able to find a cable gland so it can enter a junction box and run through conduit. Conduit is almost always better because it protects the wire, but thick copper wire is pretty tough stuff.

    I think it is fine to run bare copper wire inside the house for ground, but not for common or for DC negative. Those must be insulated. Conventional NM cable (Romex or similar) consists of insulated conductors for the mains plus a bare copper wire for ground. Similarly for pre-stuffed armored cable. You'll be doing the same thing.

    The only challenge is that your ground wire should be large (AWG 6 or larger). That's overkill for house grounds and will take up a lot of space in aluminum flex conduit. It might be difficult to pull through. Otherwise, fine.
    7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV


    • #3
      Hi Bob – thank you for the response. If my DC wires are insulated, why would it matter if the ground is in the same conduit? I’m using 2 inch PVC so there would be a lot of space. I’m using solid 6 awg copper for the earth ground.
      thank you


      • #4
        Yes, it is OK to put the ground in the conduit. In my case, I couldn't figure out how to do it because my wire is stranded and I wanted the conduit sealed. But that doesn't mean that it has to be outside the conduit.

        The ground starts outside of the conduit so to run it through conduit, I must get it into the conduit with a sealed junction box. That means that there needs to be a cable gland or other sealing device that screws into the junction box and seals around the wire. I could find these for different size plastic-coated cables, but not for bare stranded wire.

        Your ground is solid wire, 0.184" (4.674mm) OD. You may be able to find a cable gland that fits it, but that's a very small gland. Also, cable glands are typically engineered to work with flexible cable. I don't know if they are rated to seal around metal wire.

        Please forgive me for stating the obvious, but the reason for sealing is that you don't want moisture getting into the junctino box, causing leakage and accelerating corrosion of the connections.

        This may not matter for you. Many junction boxes are not sealed. Instead, they have drain holes at the bottom, so any condensation will drain out. My system is on my roof, so can have ice and snow collecting around the box. Your system is on poles, so may not have the same problems.
        7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV


        • #5
          While the link is still in my keyboard buffer

          Mike Holt Bonding vs Grounding.
          Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
          || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
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          • #6
            Thank you Mike
            I just realized I posted in the other forum...thank you for your response there as well. I'll stop this thread and stick with the other