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  • #16
    For those of you concerned about ground fault protection, I found this 2011 draft from Midnight Solar talking about some dangers of the NEC code regarding this.

    Just posting this for educational purposes if your are interested. I do not know if the issues raised in this document were addressed in the latest code release.

    http://www.midnitesolar.com/pdfs/DC-GFP-Draft3-5.pdf

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    • #17
      Originally posted by johngalt View Post
      Just posting this for educational purposes if your are interested.
      This is in no way directed at you, so do not take it that way. This is also a reason I never discuss grounding much. But if the person or persons who wrote this or endorsed it is a licensed electrical engineer or electrician should have his/her credentials reviewed and license revoked because they are an idiot and cannot even interpret what the code says. Here is how the code reads:

      690.5 Ground-Fault Protection. Grounded dc photovoltaic
      arrays shall be provided with dc ground-fault protection
      meeting the requirements of 690.5(A) through (C) to
      reduce fire hazards. Ungrounded dc photovoltaic arrays
      shall comply with 690.35.

      Exception No. 1: Ground-mounted or pole-mounted photovoltaic
      arrays with not more than two paralleled source
      circuits and with all dc source and dc output circuits isolated
      from buildings shall be permitted without groundfault
      protection.

      Exception No. 2: PV arrays installed at other than dwelling
      units shall be permitted without ground-fault protection
      where the equipment grounding conductors are sized in
      accordance with 690.45.

      (A) Ground-Fault Detection and Interruption. The
      ground-fault protection device or system shall be capable of
      detecting a ground-fault current, interrupting the flow of
      fault current, and providing an indication of the fault.
      Automatically opening the grounded conductor of the
      faulted circuit to interrupt the ground-fault current path
      shall be permitted. If a grounded conductor is opened to
      interrupt the ground-fault current path, all conductors of the
      faulted circuit shall be automatically and simultaneously
      opened.

      Manual operation of the main PV dc disconnect shall
      not activate the ground-fault protection device or result in
      grounded conductors becoming ungrounded.

      (B) Isolating Faulted Circuits. The faulted circuits shall
      be isolated by one of the two following methods:

      (1) The ungrounded conductors of the faulted circuit shall
      be automatically disconnected.

      (2) The inverter or charge controller fed by the faulted
      circuit shall automatically cease to supply power to
      output circuits.
      MSEE, PE

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      • #18
        Originally posted by Sunking View Post
        This is in no way directed at you, so do not take it that way.
        No offense taken. I was hoping somebody could validate it or shoot it down. It looked pretty official to the novice (me) when it is in Draft form to the NEC from people who claim to represent Midnight Solar. Many organizations have a Request for Comment process where people in the field can suggest improvements.

        It's impossible to trust anything you read these days without becoming an expert in every subject.

        I guess that's why the Federal Government is pushing for everyone to borrow money to get their Doctorate Degree in 18 months or less from the local cable TV college. lol.

        I am determined to self-educate myself on each section of my system until I feel comfortable I did it right. If not, tough cookies for me.

        Now you know why my politics revolve around individual freedoms and not the collective. The collective only works if you can trust all bodies involved. The bottom line is, you can't. The only one you can trust and hold accountable for your actions is yourself. As it should be.

        Thanks for blowing a huge hole in their argument.

        See, this was "educational"

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        • #19
          OK I am only going to make one comment about the article and point out a MAJOR Flaw in his document. Go to Figure 1 on page 7. Note the purple dotted line and the ground reference on the negative circuit conductor. It shows the ground reference connection through a over current protection device. In this case it is schematically represented as a fuse. (The "S" looking thing).

          So here is the Meat. That would violate NEC electrical code. Any ground circuit conductor is required to be SOLIDLY BONDED. There cannot be any device that could possible interrupt that connection. NEC requires at least the ungrounded circuit conductor be disconnected in the event of a ground fault. It does not require both to be disconnected, but is permitted.

          OK one more comment. No ground reference of any kind is needed for Ground Fault Detection or Protection to operate. All ground fault circuits work on one basic principle. It measures the current in both the Supply and Return conductors. If the currents are equal in both conductors, there is no fault. If there is a difference in current. there is a fault.

          Now here is some food for thought. Grounded system are dangerous and unreliable. For example every elevator and fire pump motors out there is required by code to use a non grounded power system. Think about that for a moment. The most important life safety systems are required not to use grounded systems. Non grounded systems are what industry uses because it is safer and not prone to unnecessary outages caused by faults.
          MSEE, PE

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          • #20
            Thank you, Dereck. Your insight and common sense is always appreciated.

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