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Thread: Single PV Arrray to Two Services - Paths to Ground

  1. #1
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    Single PV Arrray to Two Services - Paths to Ground

    Hello All, first post!

    I am working on a project where a single contiguous roof array will be divided up onto two separate inverters and interconnect to two separate electrical services. It is a residential project where a detached barn (~100' away from house) has it's own service, the house has the other and the array is located on the barn. Because of the single roof array, the array/racking EGC will be bonded to both services grounding electrodes. Is this permitted by the NEC? If not do any solutions exist other than physically separating the array sections?

    Thank you!
    Dylan

  2. #2
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    Quote Originally Posted by _Dylan View Post
    Hello All, first post!

    I am working on a project where a single contiguous roof array will be divided up onto two separate inverters and interconnect to two separate electrical services. It is a residential project where a detached barn (~100' away from house) has it's own service, the house has the other and the array is located on the barn. Because of the single roof array, the array/racking EGC will be bonded to both services grounding electrodes. Is this permitted by the NEC? If not do any solutions exist other than physically separating the array sections?

    Thank you!
    Dylan
    In one hand I am not excited about the neutrals of each service being effectively tied together and neutral current flowing across the grounding and bonding conductors (unless they are fed by different transformers and it's not a MGN system), but I don't see any NEC issue.

    Out of curiosity, why go through the hassle of also interconnecting to the house service?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  3. #3
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    Thank you for the response! You bring up a good point, this was a customer request during conversations with sales. I will look into exactly why this was requested as there is nothing I can see preventing us from interconnecting the entire system to one service.

    If we must go forward in this way we've decided to run two separate EGCs down from the roof, where our Cu jumper will not bond all of the rails together and instead only the modules/rails associated with each system, which from the looks of our racking system should be possible. There will still be contact but no UL listed bonds. Thoughts?

  4. #4
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    I'm not sure if it's better or worse to have neutral current potentially flowing on a pretty solid EGC or on some weakly bonded racking connections. AHJ might cite objectionable current either way, although I think it's pretty open to interpretation.

  5. #5
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    Quote Originally Posted by jaggedben View Post
    I'm not sure if it's better or worse to have neutral current potentially flowing on a pretty solid EGC or on some weakly bonded racking connections. AHJ might cite objectionable current either way, although I think it's pretty open to interpretation.
    FWIW I worked on a project once where we had one carport structure with two PV systems feeding two services. The AHJ made us go to great lengths to ensure that the two systems did not touch electrically, even through their EGC's.

  6. #6
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    Thanks all for the feedback, we've decided to physically separate the array into 2 sections to be safe.

  7. #7
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    So, if I was to split a pv array into several smaller sections based upon battery bank and loads, while in One residence, would they need separated due to feeding different inverters? Or would they be fine as the whole thing would be sharing the mounting grid and the ground rod system? Am working on a fully off grid system, 8ncluding both 12 and 24 volt circuits, and UK and USA circuits as well. My math says a 6000 watt inverter only covers one to two standard outlet circuits under maximum demand and diversity rules, yet have a six bed three floor home with a two bed apartment..lol... and Jamaica requires a breaker panel on each floor... for access reasons...lol

  8. #8
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    Quote Originally Posted by Adamjamma View Post
    ...Or would they be fine as the whole thing would be sharing the mounting grid and the ground rod system? ...
    The grounding electrode system doesn't present a problem if you're in one structure. You connect both sources to the same system, not a problem.

    Now if each inverter has a neutral/ground bond, then current could travel over the EGC, which is a code violation and not desirable. Ideally you only have one neutral/ground bond (main bonding jumper) in the premises. Could be an issue for you. Depends on more details you haven't fully described.

  9. #9
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    Quote Originally Posted by jaggedben View Post
    The grounding electrode system doesn't present a problem if you're in one structure. You connect both sources to the same system, not a problem.

    Now if each inverter has a neutral/ground bond, then current could travel over the EGC, which is a code violation and not desirable. Ideally you only have one neutral/ground bond (main bonding jumper) in the premises. Could be an issue for you. Depends on more details you haven't fully described.
    He's in Jamaica. Is the NEC relevant?

  10. #10
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    Jamaica codes are loose but I use the iec as my guide, mainly, and the nec and the bs 7671 give me a best practices type of guideline, especially as code originally followed the bs standards but used American parts for convenience. Closest code might be Canada as to relevance but basically, the local inspector has been ok with everything I do, as long as I can show him in my copy of the NEC or BS7671 how it works, if it is something different to what he normally sees. Biggest thing is remembering to put my red and black tape on all the wires to show local colors because I usually use UK colors..lol...

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