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Combiner box architecture question - independent PV negative returns

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  • Combiner box architecture question - independent PV negative returns

    I was looking at the Midnight Solar MNPV6, and noticed a comment in an application sheet that it has a common bus bar for PV return current (-), but the positive bus can be split for 2 array circuits (which I need).

    A footnote states: "Most charge controllers can have PV minuses common (Exception XW
    and BlueSky)"

    If I plan for two XW's, does this mean I need to look for another combiner? Suggestions? I need six 15A breakers.

    It sounds like the safety ground must have its own buss bar or connection in the combiner, yet is not connected to the PV return(s), which isn't surprising but something I hadn't considered.

  • #2
    There is a ground buss bar in that combiner box. Instead of using the negative buss bar, you could use a Burndy connector to connect from the 10AWG to the larger wire for one of the strings, and use the box's bus bar for the other. BIBS44 for 4 connections.
    Solar Queen
    altE Store

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    • #3
      Originally posted by Amy@altE View Post
      There is a ground buss bar in that combiner box. Instead of using the negative buss bar, you could use a Burndy connector to connect from the 10AWG to the larger wire for one of the strings, and use the box's bus bar for the other. BIBS44 for 4 connections.
      There you go. So make a "second" negative buss bar, that I assume would be taped or insulated in some fashion and "float" in the box? Simple concept - thanks Amy!

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      • #4
        They are insulated and can just float inside.
        Solar Queen
        altE Store

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        • #5
          Originally posted by Amy@altE View Post
          They are insulated and can just float inside.
          Polaris also makes multi-screw insulated connectors and they are very popular with electricians. Nothing against the Burndy, just mentioning an alternative.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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          • #6
            Thanks for the replies. I don't plan to do this myself, but was interested in knowing what physical boxes could be used. MS customer support informed me their 12 slot box has two separate negative busses, and they didn't seem thrilled at the thought of using a two circuit solution in the MNPV6 from a code perspective. But I assume you folks believe it will pass inspection. That's good enough for me (trusting as I am). Intuitively, the buss is just a matter of connecting wires. As long as they connect and are insulated, that should serve the purpose.

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