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Thread: Bonding screw in disco after tapping

  1. #1
    Join Date
    May 2017
    Kernersville NC USA

    Bonding screw in disco after tapping

    Recently had a PV install that the AHJ wanted us to remove the bonding screw in the fused disconnect after we had tapped in the MDP. Every other AHJ that we had dealt with wants the bonding screw in the disconnect. Basically, we had tapped before the main breaker in the MDP and then brought the conductors to a fused disconnect. The disconnect had the neutrals together and the grounds landing on the ground bar. He said by having the bonding screw in then basically the neutrals and the grounds were together and if there was a fault, there would only be one path instead of two. Since it was a PV install, leaving the bonding screw out had to be done. Since this was not a service disconnect and not the first point of disconnect, the bonding screw did not need to be installed. Is this correct? If anybody has some clarification, it would be appreciated.

    Order of wiring from the PV side:
    Conductors from the roof hitting a string inverter and then going to a summary panel where two other strings are there from an existing micro-inverter job. Backfeeding roughly 60a. From summary panel, goes to a fused disconnect. There is a ground and a neutral entering the disconnect and leaving the disconnect to the MDP. Then the L1 and the L2 conductors are tapped and the neutral and the ground wire is landed on the neutral bar since they are combined, being the first point of disconnect.

    Any question, please ask!

  2. #2
    Join Date
    Dec 2012
    Placerville, CA, USA
    This is an area where the NEC language is confusing and local AHJs even in the same state have firmly taken opposite positions.
    Until the matter is explicitly addressed in Code, I think the best you can hope for is a consistent policy across inspectors for a given AHJ.

    As I see it there are three basic options:
    1. Treat it exactly like a service disconnect:
    No incoming EGC from upstream, including raceway.
    Local GEC or jumper from GES.
    Bond between neutral and downstream EGC.
    2. Treat it like a feeder disconnect:
    EGC from upstream.
    Isolated neutral and ground buses.
    No GEC.
    3. Treat it like a feeder disconnect for a separate building:
    Incoming EGC and neutral.
    Isolated buses.
    Local GEC attached to ground bar.

    There may be other combinations, but hard to justify IMHO.

    Sent from my XT1585 using Tapatalk
    Last edited by GoldDigger; 05-17-17 at 07:20 PM.

  3. #3
    Join Date
    May 2011
    My advice for this size system: keep putting the screw in. Much easier to take it out when the inspector asks than to find where you left it (if you still have it) after you didn't put it in. As long as you still have a good EGC when they ask you to take it out, it's safe to do so.

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