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Thread: 705.12(D) questions

  1. #11
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    I don't think so...the way I read 2014 it applies to busbars. 2017 gave center-fed panelboards its own section (d) and (e) is on busbars.

  2. #12
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    Quote Originally Posted by shortcircuit2 View Post
    I don't think so...the way I read 2014 it applies to busbars. 2017 gave center-fed panelboards its own section (d) and (e) is on busbars.
    Sounds like 2017 may be different, I do not have a 2017 yet, but it seems very clear that under 2014 (D)(2)(3) is only for panelboards:


    (3) busbars. One of the methods that follows shall be used to determine the ratings of busbars in panelboards .
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  3. #13
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    Yes your right. 2017 is the same. Although switchboards and switchgear is included in the opening paragraph of 705.12(B).

    The wording may need to be revised to include switchboards and switchgear...and probably other equipment like Motor Control Centers. Just delete "panelboards" in this section and end the sentence with busbars.

  4. #14
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    Quote Originally Posted by shortcircuit2 View Post
    Yes your right. 2017 is the same. Although switchboards and switchgear is included in the opening paragraph of 705.12(B).

    The wording may need to be revised to include switchboards and switchgear...and probably other equipment like Motor Control Centers. Just delete "panelboards" in this section and end the sentence with busbars.
    Yeah I am not sure if they meant to word it that way. "multi-ampacity busbars" do strongly imply switchboards.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  5. #15
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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.
    The definition in 100 would seem to say no:

    Feeder. All circuit conductors between the service equipment,
    the source of a separately derived system, or other
    power supply source and the final branch-circuit overcurrent
    device.

    Plus, busbars being a part of listed equipment do not fall under the NEC anyway, so none of the NEC requirements for feeders apply. This is one of the reasons there is so little guidance on supply side interconnections.

  6. #16
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    Quote Originally Posted by pv_n00b View Post
    The definition in 100 would seem to say no:

    Feeder. All circuit conductors between the service equipment,
    the source of a separately derived system, or other
    power supply source and the final branch-circuit overcurrent
    device.

    Plus, busbars being a part of listed equipment do not fall under the NEC anyway, so none of the NEC requirements for feeders apply. This is one of the reasons there is so little guidance on supply side interconnections.
    (Just playing devil's advocate here, I don't have a dog in this fight from a safety point of view...)

    Neither of those points are logical to me.

    A busbar conducts electricity. By the dictionary definition it is most certainly a conductor, and there's no NEC definition of a conductor to contradict that.

    On the other point, there are all kinds of NEC requirements that apply to the use, if not the design, of listed assemblies. For example the panelboard rules in 705.12(D)(2)(3). And the OP talked about tapping a switchboard bus, which may or may not be a modification of a listed assembly.

  7. #17
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    Quote Originally Posted by jaggedben View Post
    (Just playing devil's advocate here, I don't have a dog in this fight from a safety point of view...)

    Neither of those points are logical to me.

    A busbar conducts electricity. By the dictionary definition it is most certainly a conductor, and there's no NEC definition of a conductor to contradict that.

    On the other point, there are all kinds of NEC requirements that apply to the use, if not the design, of listed assemblies. For example the panelboard rules in 705.12(D)(2)(3). And the OP talked about tapping a switchboard bus, which may or may not be a modification of a listed assembly.
    Right, those are some points for the other side. Some others are: If I run a feeder tap off the bus of a switchboard, doesnt that make the bus a feeder? Another is busways. Article 368 uses phrases like "....when a busway is used as a feeder....".
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  8. #18
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    Quote Originally Posted by jaggedben View Post
    On the other point, there are all kinds of NEC requirements that apply to the use, if not the design, of listed assemblies. For example the panelboard rules in 705.12(D)(2)(3). And the OP talked about tapping a switchboard bus, which may or may not be a modification of a listed assembly.
    There is no guidance in the NEC for tapping a busbar for PV backfeed, and that is on purpose. So the NEC does not specify if it is a modification or not, that is up to the AHJ and the equipment manufacturer.

    If there is a place in the NEC that specifies how to design listed equipment please point it out. +2 points for that.

    If someone thinks a busbar is a feeder that is an interpretation of the NEC, not verbatim from the NEC. We argue about interpretations constantly, and it's common for people with interpretations to insist that they not interpretations and are verbatim from the NEC, if you just read the NEC with one eye closed and the other squinting through a blue colored glass. Round and round we go.

    The NEC does not define conductor or busbar. Air is a conductor if you use a high enough potential.

  9. #19
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    Quote Originally Posted by electrofelon View Post
    Right, those are some points for the other side. Some others are: If I run a feeder tap off the bus of a switchboard, doesnt that make the bus a feeder? Another is busways. Article 368 uses phrases like "....when a busway is used as a feeder....".
    A busway is a type of equipment, it does not have to use busbar. Ever hear of cable bus? So busway used as a feeder does not support the argument that busbar is a feeder. Good try though, I had to look at 368.

  10. #20
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    Quote Originally Posted by pv_n00b View Post
    There is no guidance in the NEC for tapping a busbar for PV backfeed, and that is on purpose. So the NEC does not specify if it is a modification or not, that is up to the AHJ and the equipment manufacturer.

    If there is a place in the NEC that specifies how to design listed equipment please point it out. +2 points for that.
    Well there isnt a lot of detail, but article 408 part IV does have construction specifications for panelboards. 312 also has construction specifications and wire bending space at terminals. I dont know why that put this stuff in there. Seems like the place for that is nema/UL/whatever product standards.

    If someone thinks a busbar is a feeder that is an interpretation of the NEC, not verbatim from the NEC. We argue about interpretations constantly, and it's common for people with interpretations to insist that they not interpretations and are verbatim from the NEC, if you just read the NEC with one eye closed and the other squinting through a blue colored glass. Round and round we go.
    Just for full disclosure, a while back there was a thread on this and I was on the side that a busbar is NOT a feeder. So I am not taking the opposite side now just to argue, but I can see it both ways. I guess my stance on it is that a busbar IS a feeder, but the thing is many NEC rules dont apply to it. If a busbar is not a feeder then what is a tap off feed thru lugs of a panelboard or a busbar? As written, the tap rules kinda imply you have to have a feeder, to make a feeder tap. One of the regular users on here (I dont remember who) tried to get language added that the tap can start at the equipment terminals or lugs, or something like that. It was rejected because the CMP thought it was un-necessary. This implies that the equipment bus is a feeder to me. IF we take it too far though, we get into problems and inconsistancies though. For example, a panelboard would have to be derated for continuous loads.



    Quote Originally Posted by pv_n00b View Post
    A busway is a type of equipment, it does not have to use busbar. Ever hear of cable bus? So busway used as a feeder does not support the argument that busbar is a feeder. Good try though, I had to look at 368.
    I dont follow you here. Busways and cablebus are different. The point is that 368 refers to busing in equipment as feeders.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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