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  • I have a question about grounding....

    Ok so if you've read my previous post you know that I'm all messed up.

    I'm not going to get into it all again so I'll just get right to the point.

    My previous inverters, trandformerless ungrounded system, in the installation manual stated that you needed a grounding electrode. My interpretation of this is a continuous uncut wire between the grounding rods and the inverter. I know theres some exceptions to this but for the sake of what I'm getting at we'll ignore exceptions.

    My new inverters the sunnyboy 7.7 transformerless, ungrounded, independent mttp trackers or whatever they are. The installation video only shows it being connected to the ground wire for the ac side. And it only refers to the grounding as Equipment grounding conductor. The difference between a EGC vs a grounding electrode is that a EGC can have splices in it just provided its sized correctly and the splices are made correctly? Am I correct in saying this?

    Because I'm running up against 2 things , one being I can provide a grounding electrode by driving new rods and just running from there to the inverter. Uncut unspliced ect. However, if I do this, do these ground rods need to be bonded to the existing ac grounding system? If so can this bonding conductor have any splices in it?

    Obviously I'd rather just use the ground wire coming off the ac side and be done with it. But it seems like over the last 8-10 years the standards have changed and it's very confusing. I know I had talked to my electrical inspector about this b4 and he definitely said that with my previous inverters that required a grounding electrode conductor that it needed to be uncut from the rods to the inverter but like I said the new one say EGC... any help would be great thanks.

  • #2
    Originally posted by Markyrocks69 View Post
    My new inverters the sunnyboy 7.7 transformerless, ungrounded, independent mttp trackers or whatever they are. The installation video only shows it being connected to the ground wire for the ac side. And it only refers to the grounding as Equipment grounding conductor. The difference between a EGC vs a grounding electrode is that a EGC can have splices in it just provided its sized correctly and the splices are made correctly? Am I correct in saying this?

    Because I'm running up against 2 things , one being I can provide a grounding electrode by driving new rods and just running from there to the inverter. Uncut unspliced ect. However, if I do this, do these ground rods need to be bonded to the existing ac grounding system? If so can this bonding conductor have any splices in it?

    Obviously I'd rather just use the ground wire coming off the ac side and be done with it. But it seems like over the last 8-10 years the standards have changed and it's very confusing. I know I had talked to my electrical inspector about this b4 and he definitely said that with my previous inverters that required a grounding electrode conductor that it needed to be uncut from the rods to the inverter but like I said the new one say EGC... any help would be great thanks.
    There has been a lot of flip flopping in the NEC on this issue over the years, and has led to a lot of confusion to people not intimately familiar with it.

    There should be a terminal(s) in the inverter to land the EGC coming from the array. There should also be a ground terminal on the AC side. This should connect to the ground bus in your main panel. Typically the EGC coming from the array must be continuous, but that does allow for irreversible splices (compression type). I don't believe there is any requirement for the EGC going from the inverter to the main panel to be continuous (splices allowed).

    If you were going to drive new rods, they would need to be connected with an unbroken wire, and they would also need to be connected to the existing ground rods via and unbroken wire.

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    • #3
      Originally posted by emartin00 View Post

      There has been a lot of flip flopping in the NEC on this issue over the years, and has led to a lot of confusion to people not intimately familiar with it.

      There should be a terminal(s) in the inverter to land the EGC coming from the array. There should also be a ground terminal on the AC side. This should connect to the ground bus in your main panel. Typically the EGC coming from the array must be continuous, but that does allow for irreversible splices (compression type). I don't believe there is any requirement for the EGC going from the inverter to the main panel to be continuous (splices allowed).

      If you were going to drive new rods, they would need to be connected with an unbroken wire, and they would also need to be connected to the existing ground rods via and unbroken wire.
      So I I use the ground wire from the ac side that can have splices. Do I need to provide any other ground? The ground coming from the ac side that goes back to the main panel couldn't be considered the bonding point of 2 different sets of rods? Also I see people put in an "auxiliary " rod to be the EGC for the panels, from what I saw from the 2014 nec an auxiliary rod is exempt from bonding to the main grounding system. What separates an auxiliary rod from the rods I'm describing? Is there some distinction?

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      • #4
        Originally posted by Markyrocks69 View Post
        So I I use the ground wire from the ac side that can have splices. Do I need to provide any other ground? The ground coming from the ac side that goes back to the main panel couldn't be considered the bonding point of 2 different sets of rods? Also I see people put in an "auxiliary " rod to be the EGC for the panels, from what I saw from the 2014 nec an auxiliary rod is exempt from bonding to the main grounding system. What separates an auxiliary rod from the rods I'm describing? Is there some distinction?
        The distinction is that the "auxiliary" rod isn't required by code, so is exempt from the bonding requirement. But if not bonded to the rest of the ground system it can cause the same fires and failures that any other unbonded ground rod can. Here's a video on the subject where Mike Holt gets pretty fired up about it: https://www.youtube.com/watch?v=WlnFNTay-9Q

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        • #5
          Originally posted by sdold View Post
          The distinction is that the "auxiliary" rod isn't required by code, so is exempt from the bonding requirement. But if not bonded to the rest of the ground system it can cause the same fires and failures that any other unbonded ground rod can. Here's a video on the subject where Mike Holt gets pretty fired up about it: https://www.youtube.com/watch?v=WlnFNTay-9Q
          I've watched that video 8 times, its exactly why I bring it up. Can I put in some rods, call them auxiliary and be done with it? If the auxiliary rod isn't bonded to the rest of the system it has zero chance of sending voltage through your house in the instance of a lightning strike.

          His argument was having multiple ground rods bonded together because you could have different voltagev in the ground during a lightning strike causing voltage to travel through the house. If different sets of rods arnt bonded to the main ground for the house it eliminates that aspect....
          Last edited by Markyrocks69; 06-24-2019, 02:01 PM.

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          • #6
            Originally posted by Markyrocks69 View Post

            I've watched that video 8 times, its exactly why I bring it up. Can I put in some rods, call them auxiliary and be done with it? If the auxiliary rod isn't bonded to the rest of the system it has zero chance of sending voltage through your house in the instance of a lightning strike.
            You're missing the point of the rod to rod bonding, which is to give the lightning strike currents in the ground another path besides the wiring from the panels to the inverter.

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            • #7
              Originally posted by sdold View Post
              You're missing the point of the rod to rod bonding, which is to give the lightning strike currents in the ground another path besides the wiring from the panels to the inverter.
              Well this was also talked about in the video, if lightning strikes your panels, that 6 gauge wire isn't saving anything. Besides that the NEC is designed to be standards for safe electrical installations not to prevent negative things happening from lightning strikes. I'd imagine that the bond between sets of ground rods is to keep the resistance the same so that the electricity in a fault situation travels the right way so it works as intended. Also to ensure that the over current devices work as intended. But I guess that kinda answers my own question. If the ground rods aren't bonded correctly it could keep the associated breakers from tripping, but I had always planned on using the ground from the ac side so I guess it would still work as intended and the bond between a hypothetical new set of rods would be bonded at the inverter....grrr this is so frustrating. I'm going to watch that video again and call my electrical inspector...

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              • #8
                My bad there was actually a different video that talked about different aspects of pv grounding by holt. But I had watched the video you posted b4 tho aswell.
                I did find this....

                "
                For PV systems that are not solidly grounded, the equipment grounding conductor for the output of the PV system, connected to associated distribution equipment, shall be permitted to be the connection to ground for ground-fault protection and equipment grounding of the PV array."

                Which I did see an example on a different holt video where ungrounded systems could be hooked up this way. The only thing I have to add is that the requirement of a shutoff switch between the electrical panel and the inverter would lead me to believe in this scenario that a splice would have to be allowed...

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                • #9
                  Originally posted by Markyrocks69 View Post
                  if lightning strikes your panels, that 6 gauge wire isn't saving anything.
                  It's more likely to be a nearby strike that you'll be dealing with. Surface current will flow through the big resistor below your house (the dirt) and create a large voltage difference between the two rods. You'll get a large current through whatever connections are there between the two rods. If you bond them under the dirt, that's where most of the current will flow, instead of the panel to inverter wiring. If that bond's not there, the only path left is the wiring. That's what Mike's trying to show.

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                  • #10
                    Ok well thanks for the help. I talked to my electrical inspector and he said that I was correct in saying that the ground from the ac circuit can be used as the equipment ground for the inverter and the PV array. Also since its and equipment ground, passes through safety switches ect that it can have splices.

                    On my other question about combining the neutral, from 2x 6 gauge wires to a single 2 gauge wire and then spit again later on down the line. He basically said that the circuit breakers need to be interlocked together or it has to be a 4 pole breaker instead of 2x2 pole breakers. Idk if this topic was discussed in this thread but I'm pretty happy that I have some actual answers instead of guessing.

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                    • #11
                      Originally posted by sdold View Post
                      Here's a video on the subject where Mike Holt gets pretty fired up about it: https://www.youtube.com/watch?v=WlnFNTay-9Q
                      Yep and I am in that video with the other mods feeding Mike material.

                      MSEE, PE

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