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Thread: Grounding metal roof with PV system EGC?

  1. #1
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    Grounding metal roof with PV system EGC?

    I plan to install a solar array on my standing seam metal roof but have concerns about any future PV wire damage (from the rodent family) that could result in an energized roof. Would it be acceptable or best practice to bond the roof to the PV system equipment grounding conductor? Because of the size of the roof, should any grounding of it be done with a separate grounding conductor and ground rod? Thanks.

    William L

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    I am closing this thread, in accordance with the Forum Rules.

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  3. #3
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    After corresponding with the OP I am reopening this thread.
    If you don't think too good, don't think too much.

  4. #4
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    Conceptually, it would be a good idea to bond the roof to the PV EGC. I would not bond it to a different electrode than the PV array. Use the same electrode as the PV array, which ideally should be the premises electrode system.

    With that said, I think you will find it difficult to source hardware that is listed for bonding standing seam roofs. The catch-22 is that the protective anti-corrosive coating of the roof panels isn't supposed to be penetrated, and you can't bond from the top without doing that. So any company advertising a method for bonding would also be advertising that your roof panel warranty would be void.
    Your best bet might be products intended for lightning protection systems.

    Finally, I think that in practice, if the PV panels are mounted using something similar to S-5! clamps, you'll probably have a lot of bonding between the PV panels and roof, even if the clamp manufacturer won't admit it. Experience makes me somewhat inclined to say 'don't worry about it'. On the other hand, my observations have withstood neither the test of a few months exposure to the elements, nor the scrutiny of any inspector asking for an approved bonding method.

  5. #5
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    jaggedben,

    Thanks for the advice. I read product information on the S5 PV Direct and saw that their bonding feature is only module frame to module frame. Reading up on lightning protection systems, I see that they don't include bonding to the roof panels either - just capturing the lightning strike and directing it to ground.

    You are right that this appears to be a catch 22. Disturb the metal coating and void the warranty. Searches on this issue indicated that some states like NY and MA listed metal roofing as qualifying regarding 2014 NEC 690.43 wording of metal parts "likely to become energized". It appears that no acceptable solutions to this interpretation were proposed. I see that 2017 690.43 lists the specific metal parts and metal roofing is not included and the phrase "likely to become energized" was removed. I guess the solution to the risk was to disregard the possibility of the coated metal roof conducting module output as only remote.

    I still can't help but desire an acceptable method to achieve bonding to the roof.

    Thanks again.

    William L

  6. #6
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    This is a contested issue, most seem to feel that adding the standing seam panels to the equipment ground is not necessary. I have seen it done a few times. The trick is not voiding the roof warranty and not causing a situation that will lead to a buildup of leaf litter or snow on the roof.

  7. #7
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    I would think that bonding/grounding the equipment likely to energize the roof renders the issue moot.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  8. #8
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    Quote Originally Posted by LarryFine View Post
    I would think that bonding/grounding the equipment likely to energize the roof renders the issue moot.
    I don't see how.

  9. #9
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    Quote Originally Posted by pv_n00b View Post
    This is a contested issue, most seem to feel that adding the standing seam panels to the equipment ground is not necessary. I have seen it done a few times. The trick is not voiding the roof warranty and not causing a situation that will lead to a buildup of leaf litter or snow on the roof.
    I know from an unpleasant experience that S-5 attachments on a standing seam roof will effectively bond the racking system to the roof panels.

  10. #10
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    Quote Originally Posted by ggunn View Post
    I know from an unpleasant experience that S-5 attachments on a standing seam roof will effectively bond the racking system to the roof panels.
    My apologies (ahead of time) if this is considered prying, but I'm curious. Did it result in a warranty issue or roof damage?

    William L

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