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Thread: 705.12(D) questions

  1. #1
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    705.12(D) questions

    1. Does 705.12(D)(2)(1) apply to the feeder bus (the bus on the load side of the service disconnect) of a switchboard?

    2. In the body of (D) it states ".....and where this distribution equipment is capable of supplying multiple branch circuits or feeders...." What would be an example of something not capable of supplying multiple branch circuits or feeders and thus not subject to any of the rules in (D)?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  2. #2
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    I'd answer (1) affirmatively, I think. Switchboards are a bit of a grey area for me since 705.12(D)(2)(3) refers specifically to panelboards.

    Bussing in a disconnect would not qualify for your item (2), in my opinion. I've always read it as the equipment is capable of feeding multiple circuits directly (e.g. as in a panelboard) and not by supplying some other distinct downstream equipment.

    (For 2017 NEC, read 705.12(B) instead of (D).)

  3. #3
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    Quote Originally Posted by jaggedben View Post
    I'd answer (1) affirmatively, I think. Switchboards are a bit of a grey area for me since 705.12(D)(2)(3) refers specifically to panelboards.
    Be aware that switchboards may also have multiple busbar ampacities involved. Such as a main horizontal bus with the full ampacity, and branch vertical bussing of a lesser ampacity.

  4. #4
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    Quote Originally Posted by Carultch View Post
    Be aware that switchboards may also have multiple busbar ampacities involved. Such as a main horizontal bus with the full ampacity, and branch vertical bussing of a lesser ampacity.
    Right, but that could be used as an argument that it doesn't apply. IMO, It seems overly restrictive to not allow a tap to the feeder bus in a switchboard where the main matches the bus rating
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  5. #5
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    Quote Originally Posted by Carultch View Post
    Be aware that switchboards may also have multiple busbar ampacities involved. Such as a main horizontal bus with the full ampacity, and branch vertical bussing of a lesser ampacity.
    So are busbars in switchboards feeders? That seems to be the question. On a straight reading of the definition it would seem that they could be.

  6. #6
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    Quote Originally Posted by electrofelon View Post
    2. In the body of (D) it states ".....and where this distribution equipment is capable of supplying multiple branch circuits or feeders...." What would be an example of something not capable of supplying multiple branch circuits or feeders and thus not subject to any of the rules in (D)?
    Yes interesting question. An example of distribution equipment that can not supply multiple branch circuits or feeders is a single service disconnect, with a single feeder onto a main lug panelboard. There could be a load side tap in that single service disconnect that should be subject to 705.12(B)(2)(1). This is a common connection point and the feeder rule is followed in the field when recognized by installer and AHJ.

    Maybe a rewrite of the "body" is needed.

  7. #7
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    Quote Originally Posted by jaggedben View Post
    So are busbars in switchboards feeders? That seems to be the question. On a straight reading of the definition it would seem that they could be.
    Well, I think that is a stretch of the definition. The busbars are part of a listed assembly. A feeder is in between 2 listed pieces of equipment.

  8. #8
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    Quote Originally Posted by shortcircuit2 View Post
    Well, I think that is a stretch of the definition. The busbars are part of a listed assembly. A feeder is in between 2 listed pieces of equipment.
    That is kinda my thinking. We have had some big debates on here before on the general topic "is a panelboard bus a feeder (or service conductor)?".

    If you look at the layout of (D)(2), it doesnt seem real logical if they intend a switchboard bus to be covered under (1) feeders. Seems like they could have just tweaked (3) busbars to include switchboards too.

    Edit: And to expand on what I mentioned earlier, that seems overly restrictive and would kill many taps to a switchboard bus. Sure there are many times when a main is less than the bus rating on a switchboard, but also quite often it is the same. Also we could note that article 408 doesnt require switchboards to be protected at their rating like it does for panelboards. Perhaps the code writers feel that work on switchboards is more likely to be engineered and/or done by more qualified people.
    Last edited by electrofelon; 12-28-17 at 09:55 AM.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  9. #9
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    705.12(D)(2)(3)(e) allows connections under engineering supervision to multiple ampacity busbars.

  10. #10
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    Quote Originally Posted by shortcircuit2 View Post
    705.12(D)(2)(3)(e) allows connections under engineering supervision to multiple ampacity busbars.
    Not sure if that changed for 2017, but under 2014, that only applies to panelboards.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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