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what does "for this purpose" mean?

what does "for this purpose" mean?

New postby Jerry Peck - Codeman on Tue Feb 17, 2009 3:26 pm

From an e-mail question.

Codeman,

I'm also looking for an opinion on the following, You know how some guys will feed an a/c disconnect with two sets of feeders and then nipple over to another a/c disconnect thereby using the first one as a pull box. I've always felt that 312.8 prohibited this practice but am now questioning the the part in 312.8 that says ...."unless adequate space for this purpose is provided".

I've always felt this means that the disconnect must be listed "for this purpose" (allowing the pass through of conductors). Sooo,
if the disconnect is not listed for this purpose it is not ok. If it is listed for this purpose and meets the other requirements stated in 312.8 then it would be ok.

I'm I off base on this ?
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Re: what does "for this purpose" mean?

New postby Jerry Peck - Codeman on Tue Feb 17, 2009 4:03 pm

The Simple Answer to your question is that you are correct - No, space is not provided for that purpose.

The following is the long answer and will hopefully answer your question in greater detail.

From the 2008 NEC. (bold and underlining are mine).
- 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.

Many people read the first sentence and then ignore it (or they simply do not read it), going on to the second sentence which defines the limitations of use of "space provided for this purpose".

You are correct as the first and foremost statement in that section is: "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, ... ".

The next thing that section gives is an exception (while not stated in the normal exception manner, it is nonetheless an exception to the preceding part of the statement). That exception is: "unless adequate space for this purpose is provided."

I called and talked to several UL Senior Engineers years ago asking about this very question and asking for clarification of what the Standard to which these are listed states. I was told that the UL Standard 67 for panelboards, etc. (enclosures for overcurrent devices), shall not be used as junction boxes, auxiliary gutters, etc., as stated in the NEC, and that there are no enclosures listed which provide space for that purpose, and, that there is not even a standard which can be used to test, list or label the enclosures to.

They said that if a manufacturer wanted to list their enclosures for panelboards, etc. (enclosures for overcurrent devices), for that purpose, that UL would be more than happy to work with the manufacturer to establish parameters for such testing, listing and labeling.

They stated that the standard would need state the maximum number of conductors, the limitations of size of the conductors, and the maximum current allowed through those conductors before any standard could be developed. An example would be allowing a 150 amp rated panelboard to have conductors running through it to another 200 amp panelboard, what would be the detrimental effects of temperature rise, as one condition, on the panelboard being used as a raceway? Would they have to limit the amperage of the conductors running through the panelboard to, for example, 100 amps for a 150 amp rated panelboard to maintain staying within the heat rise limitations allowed.

There were a lot of variables which would need to be addressed in developing such a standard, and that standard would be very specific on what was allowed to run through the panelboard.

Then, at that point, the last part of that code sections would come into effecting the installation: "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."

The above last section is one regarding working space and accessibility of and to the conductors. The new standard which would need to be developed would need to cover all other aspects of those conductors filling that space.

As yet, no manufacturer has requested UL work with them to develop a standard for that use, thus there are no standards for which an enclosure can be tested, listed, and labeled for that use, thus, there are no enclosures available in which "space for this purpose is provided".

Therefore, we end back at the beginning: The Simple Answer: "Simple Answer to your question is that you are correct - No, space is not provided for that purpose."

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