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Question about wiring SMA 3000TL Inverter: what is"ungrounded PV array"

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  • Question about wiring SMA 3000TL Inverter: what is"ungrounded PV array"

    I am planning a DIY installation. While I will be getting an electrician involved, I want to understand things and have been reading the manual for the SMA 3000TL transformerless inverted. I will be installing the array on a metal roof atop a wooden shed if that is relevant. I am planning to use Canadian Solar 260W modules on an iron ridge rack system that will be lagged through the metal roof into the wooden rafters of the shed. While I am a newbee I hope it is OK to post here as this is a technical question.

    I don't understand the meaning of the following paragraph in the SMA Installation manual:

    6.4.2 Conditions for the DC Connection
    The inverter is transformerless and has no galvanic isolation. Therefore, the inverter may only be
    operated with ungrounded PV arrays. Furthermore, the PV array must be installed in accordance with
    the National Electrical Code®, Article 690.35 "Ungrounded Photovoltaic Power Systems" and the
    locally valid regulations for ungrounded PV arrays. Additionally, the PV array (PV modules and
    cabling) must have protective insulation and the PV modules used must be suitable for use with this
    inverter.

    What is an "ungrounded PV array"?

    I have an existing professionally installed 4.6 kW system on a totally similar building with an SMA 4000TL inverter. It appears that there are grounding wires that connect the Iron Ridge rails and then go into a grounding rod in the earth.

    Does anyone have a link to a schematic wiring diagram for an array that show the grounding connections?

    Also, a separate question not related question: in connecting 240V AC to the panel do I need to use a ground fault type breaker?

    Thanks for any inputs and comments.

  • #2
    Originally posted by u2builder View Post

    What is an "ungrounded PV array"?
    I think this article will help:

    http://www.homepower.com/articles/so...ded-pv-systems

    "A common misconception about ungrounded PV systems is that they lack all grounding, including equipment grounding—the bonding to ground of exposed metal that could become energized in a fault situation. But all Code-compliant and well-installed PV systems must still have equipment grounding—the bare copper or green-insulated grounding conductors that bond the metal boxes, the metal conduit, the metal rails that hold modules, and the metal frames of the PV modules."

    (there's more as well - I'd recommend reading it)

    Comment


    • #3
      Originally posted by foo1bar View Post
      I think this article will help:

      http://www.homepower.com/articles/so...ded-pv-systems

      "A common misconception about ungrounded PV systems is that they lack all grounding, including equipment grounding—the bonding to ground of exposed metal that could become energized in a fault situation. But all Code-compliant and well-installed PV systems must still have equipment grounding—the bare copper or green-insulated grounding conductors that bond the metal boxes, the metal conduit, the metal rails that hold modules, and the metal frames of the PV modules."

      (there's more as well - I'd recommend reading it)
      ************************************************** *******
      "
      It totally helps and makes complete sense. I guess it is what I thought would be done because I hadn't been aware of the concept of "grounded DC", though I guess cars use grounded DC.

      I have one followup question.

      I am planning on a single string array of 8 250 W panels. (SMA tech services says that while the 3000TL inverter is oversized "it will work fine", and sent a computer analysis when I asked for assurance).

      I plan to locate the inverter in a shed pretty much directly below the metal roof on which the panels are located. I was planning to run the plus and minus PV wire from the panels (using male and female MC4 connectors built into the PV wire) to mate with the panels through water tight connectors into a 600V rated PVC junction box on the roof under the panels, and then out the bottom of the box via conduit directly to the inverter plus and minus terminals without any intermediate connections, using the DC disconnect and ground fault overcurrent protection built into the SMA inverter. The panel mounting racks will be connected with ground wiring using the proper connectors and run down to a ground rod. A ground wire will also be connected to the inverter at its ground terminal. On the AC side there will be an AC disconnect and 240V wiring in conduit to a panel in a nearby building. Does this make sense?

      Comment


      • #4
        It makes sense, but it is worth checking to see if your local AHJ has any requirements that might need special attention to be met.
        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

        Comment


        • #5
          Originally posted by sensij View Post
          It makes sense, but it is worth checking to see if your local AHJ has any requirements that might need special attention to be met.
          Thanks. We don't have any authority. Our town building official did not choose to be involved. I will be hiring a local electrician to be determined and I want to make sure he does it right. Kind of a role reversal!

          Comment

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