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  • Parallel feeding distribution panels

    Looking for free education here, if you're willing to share.

    Why aren't panels "double fed", using approved double-lugs in the subpanel?

    Example, current subpanel is bus fed from main panel with 6/3+g. In the future if you need more, it is proper to rip out the 6/3 and replace with higher rated wires. However, you don't parallel feed the panel with lets say another set of #6 wires (and upgrading the neutral/ground as needed to support the higher load).

    Is that because of potential unbalanced load between the parallel lines, choosing least resistant path, surpassing the rated load of the line chosen?

    It crossed my mind because I see the solar AC lines feed the main panel at the bus, opposite side of SE feeders. Obviously that isn't parallel from the same source as my example, but fed from an additional source.

  • #2
    Originally posted by cebury View Post
    Looking for free education here, if you're willing to share.

    Why aren't panels "double fed", using approved double-lugs in the subpanel?

    Example, current subpanel is bus fed from main panel with 6/3+g. In the future if you need more, it is proper to rip out the 6/3 and replace with higher rated wires. However, you don't parallel feed the panel with lets say another set of #6 wires (and upgrading the neutral/ground as needed to support the higher load).

    Is that because of potential unbalanced load between the parallel lines, choosing least resistant path, surpassing the rated load of the line chosen?

    It crossed my mind because I see the solar AC lines feed the main panel at the bus, opposite side of SE feeders. Obviously that isn't parallel from the same source as my example, but fed from an additional source.
    There are good reasons why conductors in parallel are less safe that a single larger conductor. But the most important factor is that the National Electrical Code does not allow it for conductors smaller than 1/0.
    From Section 310.10(H) of the 2014 NEC:
    (1) General. Aluminum, copper-clad aluminum, or copper conductors, for each phase, polarity, neutral, or grounded circuit shall be permitted to be connected in parallel (electrically joined at both ends) only in sizes 1/0 AWG and larger where installed in accordance with 310.10(H)(2) through (H)(6).
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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