705.12 and Switchboard

[nhee2]

705.12(B)(2)(3) - busbar ampacity rating specifically refers to 'busbars in panelboards'.

Does this mean the rules do not apply to switchboards? If I have a 1MW generator interconnecting through a main switchboard, switchboard feeds other plant loads through separate feeders, and contains the service disconnect to utility, does 705.12(B)(2)(3) apply to the switchboard bus rating?

 

[jaggedben]

Apparently the code making panel intended it to apply to switchboards, since they have added that language in the First Draft of the 2020 NEC. However, if you don't want it to apply, you've got the letter of the code on your side with the 2014 or 2017 NEC. I presume with a 1MW system your going to have an engineer putting his/her name behind it, so that may be good enough for the AHJ.

 

[JoeStillman]

That could be a tough rule to apply to a switchboard, since, unlike a panelboard, you may have more than one bus rating to evaluate. Horizontal and vertical busbars of a multi-section board are often different, and the main bus may reduce as you move away from the supply end.

 

[jaggedben]

That could be a tough rule to apply to a switchboard, since, unlike a panelboard, you may have more than one bus rating to evaluate. Horizontal and vertical busbars of a multi-section board are often different, and the main bus may reduce as you move away from the supply end.

Yes, and the code allows interconnections on that kind of thing if there's an engineering study.

 

[nhee2]

Thanks for the input. I have not worked often with article 705.

I assume, then, that most 'switchboard-sized' applications of 705.12(B) are using 705.12(B)(2)(3)(c) and engineering supervision.

 

[shortcircuit2]

I refer to 705.12(B)(2)(3)(e) for multiple-ampacity busbars.