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Thread: AC PVC disconnect tap from supply side

  1. #11
    Join Date
    May 2011
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    4,639
    Quote Originally Posted by hhsting View Post
    Current always goes back to the source so been told in fudamental electrical classes
    So if there is a fault in PV solar system will it go to the place there is fault then to EGC to wherever MBJ is and then to what electric utility or back to solar panels? Its confusing and very confusing to place MBJ or not AC PV disconnect.
    The available fault current from the utility will be tens of thousands of amps or higher, as it normally is.

    The available fault current from the inverter(s) will be at most only marginally greater than its rated maximum operating output. It may be on the data sheet. In other words, most likely many times less than, if not totally insignificant compared to, the utility. You will most likely be relying on utility sourced current to open any OCPD in a sudden fault.

    The MBJ may return fault current to both sources but it is typically only the grid that you have to worry about.

    For this reason I've always thought that the PV disconnect should be treated like another service entrance. But some read the code legalistically, instead of with a mind to physics and safety, and determine that's not so.

  2. #12
    Join Date
    Jun 2018
    Location
    Glen bunie, md, us
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    89
    Quote Originally Posted by jaggedben View Post
    The available fault current from the utility will be tens of thousands of amps or higher, as it normally is.

    The available fault current from the inverter(s) will be at most only marginally greater than its rated maximum operating output. It may be on the data sheet. In other words, most likely many times less than, if not totally insignificant compared to, the utility.

    The MBJ may return fault current to both sources but it is typically only the grid that you have to worry about.

    For this reason I've always thought that the PV disconnect should be treated like another service entrance. But some read the code legalistically, instead of with a mind to physics and safety, and determine that's not so.
    What if bring neutral and phase service conductor tap into AC PV main disco, tie neutral to neutral bar and from neutral bar place GEC to electrodes possibly bldg electrodes and then to have MBJ from neutral bar to ground bar in the PV AC main disco. Your not brining any EGC to AC PV main disco. Would that be ok?

  3. #13
    Join Date
    May 2011
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    4,639
    Quote Originally Posted by hhsting View Post
    What if bring neutral and phase service conductor tap into AC PV main disco, tie neutral to neutral bar and from neutral bar place GEC to electrodes possibly bldg electrodes and then to have MBJ from neutral bar to ground bar in the PV AC main disco. Your not brining any EGC to AC PV main disco. Would that be ok?
    Then you're treating it as a service disco. It's okay if the AHJ says so.

  4. #14
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
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    10,054
    Quote Originally Posted by jaggedben View Post
    Then you're treating it as a service disco. It's okay if the AHJ says so.
    FWIW, I went to a training session at SPI last week on the 2017 and proposed 2020 NEC. In all probability in 2020 this will be clarified to say that N-G bond happens in the disco. Until then it is subject to interpretation and either way is compliant.

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