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Thread: Auxiliary ground rod at pad mount

  1. #1
    Join Date
    May 2017
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    Kernersville NC USA
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    Auxiliary ground rod at pad mount

    Hello all,

    When I put the auxiliary rod at a pad mount, I always bring the #6 bare back in the ditch and irreversible it at the main GEC. Recently, I went and looked at an install where they ran a #6 thwn from the combiner at the pad through the pvc and then landed the other end in the MDP on the ground bar. They did drive a rod at the pad and split bolted the bare from the rod to the #6 thwn-2 in the combiner box and then sent it on. Is this legal to be done this way?

  2. #2
    Join Date
    May 2011
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    3,500
    First, what code cycle are you on? Only the 2014 code requires an 'auxiliary' electrode, and it's for an array and not usually anything that's just on a 'pad'. If you're not on the 2014 code then there are really no rules for what you bond such a rod to, and I would also say that driving an auxiliary rod will likely do more harm than good.

    Are you just concerned about the use of a split bolt or is there something else I'm not quite getting? It sounds like you're suggesting that you normally drive a rod at the pad but perhaps don't connect that rod to anything at the pad? In which case, I'd have to ask, what is the point of that? Probably a fuller description would help.

  3. #3
    Join Date
    Jun 2006
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    Quote Originally Posted by jaggedben View Post
    ...Probably a fuller description would help.
    +1
    I'll never get there. No matter where I go, I'm always here.

  4. #4
    Join Date
    May 2017
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    Kernersville NC USA
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    Update to issue

    Sorry for the the vagueness! Here is a fuller detail.

    I am using the 2014 code. When there is a PV array on a concrete pad, we drive an auxiliary ground rod at the pad. We then run a #6 bare from the array in the ditch and back to the home's main service. That #6 bare connected to the racking and then to the aux. ground and then ran back in the ditch and then irreversibly crimped to the home's main bare that is connected to the main GEC, therefore not creating a loop. So basically we have that #6 bare separate from the conductors in the ditch. I was wondering, is it legal to run a #6 thwn-2 back with the conductors in the conduit and land on the ground bar in the MDP instead of keeping it separated and connecting to the bare at the MDP's ground rods. I didn't think this was a problem, but wanted to get feedback on this.

    Hope this helps

  5. #5
    Join Date
    May 2011
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    As far as the code is concerned, 690.47(D) doesn't even require that the array GEC be run anywhere except between the array frame and the auxiliary electrode. So whether you run it in the ground or with the circuit conductors, either way that connection isn't required.

    You are required to run an EGC between your array and your inverter, and that EGC has to be run with the circuit conductors. So if you are running your bare #6 in the ditch instead of an EGC with the circuit wiring, that is not legal.

    The guy who sponsors this forum thinks that the auxiliary electrode required in the 2014 NEC is a very bad rule. I agree with him, and so did the Code Making Panel when they removed that rule (again) from the 2017 NEC. Your practice of running a bonding jumper through the ground is perhaps not a bad one for mitigating the concerns that are expressed in the video, although those concerns apply primarily to rooftop array and not ground mounted ones. Also note that if you have any significant amount of steel in concrete in the ground that's supporting the array, that steel probably creates a much more meaningful connection to ground than one measly little ground rod.

  6. #6
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    Quote Originally Posted by jaggedben View Post

    The guy who sponsors this forum thinks that the auxiliary electrode required in the 2014 NEC is a very bad rule. I agree with him, and so did the Code Making Panel when they removed that rule (again) from the 2017 NEC. Your practice of running a bonding jumper through the ground is perhaps not a bad one for mitigating the concerns that are expressed in the video, although those concerns apply primarily to rooftop array and not ground mounted ones. Also note that if you have any significant amount of steel in concrete in the ground that's supporting the array, that steel probably creates a much more meaningful connection to ground than one measly little ground rod.
    FWIW, I have been in the solar business as a designer for about 8 years and I have hundreds of PV system designs, both residential and commercial, under my belt. In all my experience I have only encountered one particular inspector in one AHJ (where I don't do much work, thankfully) who holds my feet to the fire over 690.47(D).

  7. #7
    Join Date
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    Quote Originally Posted by ggunn View Post
    FWIW, I have been in the solar business as a designer for about 8 years and I have hundreds of PV system designs, both residential and commercial, under my belt. In all my experience I have only encountered one particular inspector in one AHJ (where I don't do much work, thankfully) who holds my feet to the fire over 690.47(D).
    Our guys have had I think three conversations about it in different AHJs since the beginning of the year when it came back into the code in California. So far we haven't had to do much additional work, just conversations and warnings about 'next time'. I hope that by 'next time' they have had enough time to study and decide not to strongly enforce. Fingers crossed.

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