312.8

[jim k]

312.8 Enclosures for Switches or Overcurrent Devices. Enclosures for switches or overcurrent devices shall not be used as junction boxes, auxiliary gutters, or raceways for conductors feeding through or tapping off to other switches or overcurrent devices, unless adequate space for this purpose is provided. The conductors shall not fill the wiring space at any cross section to more than 40 percent of the cross-sectional area of the space, and the conductors, splices, and taps shall not fill the wiring space at any cross section to more than 75 percent of the cross-sectional area of that space.

My question has to do with the phrase ?adequate space for this purpose? and specifically the words, ?for this purpose.?

As I understand it, the section is talking about wires that enter an enclosure and then exit it without landing on, let?s say, a breaker within the enclosure. It admonishes us not to do this unless there?s ?adequate space for this purpose.? I interpret this to mean that such wires have to be placed in those areas of the enclosure that are meant to be wireways as opposed those spaces that are meant to contain the panel parts -- i.e. buses, breakers, mounting hardware, etc.

Another inspector insists that the section is more restrictive. His contention is that the only time ?feed through? wiring is allowed in a panel enclosure is when there?s a specific ?space for this purpose? (foreign wires). He cites the fact that UL 67 doesn?t include feed through wiring as part of the listing of this equipment. His common-sense argument is that someone might switch off power to a panel and reasonably assume that all conductors within the enclosure would then be de-energized ? a possibly fatal assumption. Since there are no panel enclosures that are so rated, the practice is never allowed.

If he's right, I've got to wonder why the section is so specific about the wire fill requirements toward the end.

What do you all think?

- Jim K

 

[jim dungar]

So, he does not allow a 1 gang box, with a device installed, to have any "feed thru" conductors regardless of depth or width (i.e. 4"sq with mud ring)?

 

[jim k]

So, he does not allow a 1 gang box, with a device installed, to have any "feed thru" conductors regardless of depth or width (i.e. 4"sq with mud ring)?

It's difficult for me to answer on his behalf, especially since I disagree with his position. However, I think he'd say that a 4" box is intended and UL listed to function as a junction box. That is, the space in the box is "for that purpose." So, in that case, he'd think it was just fine. He might further say that there'd be no expectation, on the part of an electrician, that when the switch was turned off that the conductors would all be de-energized.

- Jim K

Edited for clarity.

 

[dana1028]

Take a look at the NEC Handbook on this subject [yes, I know it is not official code....but then neither is this forum].

The Handbook says 'Where adequate space is provided...the total conductor fill in the enclosure may not exceed....'.

The intent is to NOT permit 'this purpose' unless there IS adequate space within the enclosure.

There is no mention of concern about a 'live' wire; generally the code panels place the responsibility of checking for live wires on the electrician doing the work.

 

[colosparker]

If you read the commentary in the 2005 NEC Handbook for 312.8 it states: "Most enclosures are intended to accomodate only those conductors that will be connected to terminals for switches or overcurrent devices within the enclosures themselves." In other words "most", but not all. UL 67 is for Panelboards. I think you have the bigger picture.

 

[jim k]

Thanks for the replies. The handbook is a little help, but it doesn't really clarify the section for me.

I have noticed one other thing. In the 1993 edition, the section reads differently. (Back then it was in 373.8 )

373.8 Enclosures for Switches or Overcurrent Devices. Enclosures for switches or overcurrent devices shall not be used as junction boxes, auxiliary gutters, or raceways for conductors feeding through or tapping off to other switches or overcurrent devices.
Exception: Where adequate space is provided so that the conductors do not fill the wiring space at any cross section to more than 40 percent of the cross sectional area of the space, and so that the conductors, splices, and taps do not fill the wiring space at any cross section to more than 75 percent of the cross-sectional area of the space.

In this version, there's no mention of "for that purpose." The section simply says that you can feed through the enclosure if there's adequate space.

The change must have come in '96. I don't suppose anyone out there has a '96 guide to changes? Did the CMP really intend to change the meaning of the section when they reworded it?

- Jim K

Edited to get rid of one of those stupid emoticons that I inadvertently coded.

 

[don_resqcapt19]

Jim,
According to the ROP, the change was only "editorial" and not an intended change in the code meaning. [propoal 9-93(a)] There was another proposal,9-94, that wanted panels to listed and marked for the purpose, and this proposal wal rejected with a comment that makes it clear that the panel intends that the wire fill rules for wireways be applied to the wireway space in a panel for the purposes of this rule.
Don

 

[jim k]

Jim,
According to the ROP, the change was only "editorial" and not an intended change in the code meaning. [propoal 9-93(a)] There was another proposal,9-94, that wanted panels to listed and marked for the purpose, and this proposal wal rejected with a comment that makes it clear that the panel intends that the wire fill rules for wireways be applied to the wireway space in a panel for the purposes of this rule.
Don

Ah! This sounds promising. Is there any chance that you could e-mail both of those ROPs to me along with the panel comments?

(e-mail address removed bo moderator)

I'd sure appreciate it.

Thanks.

- Jim K