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.
This was at a IAEI meeting and posted online - Enjoy !
Question 1. The practice of using switch disconnect enclosures as wiring gutters or splice boxes could be circumvented if the wording of 110.59 [NEC 2002] could be inserted for installation of equipment of less than 600 volts. I will have to use convoluted reasoning to arrive at the result, unless the Code has a forthright statement, such as 110.59, to ease the task. ? W.H.
Answer 1. If I understand the question, the reader is asking that the words ?unless special designs are used to provide adequate space? should be added for switch enclosures under 600 volts. Switch disconnect enclosures are covered by Article 404. Section 404.3(B) states, ?Enclosures shall not be used as junction boxes, auxiliary gutters, or raceways for conductors ? unless the enclosure complies with 312.8.?
Section 312.8 allows enclosures to be used in this manner when the conductors do not fill the wiring space at any cross-sectional area to more than 40 percent of its cross-sectional area of the space and 75 percent if splices and taps are present. Enclosures are generally intended to accommodate only those conductors that will be connected to the switches and overcurrent devices; but additional conductors passing through the enclosure can meet the present Code. If the suggested language were added to 312.8, this would limit the use of the disconnect switch enclosures. A testing laboratory would need to list special design enclosures to the size of the conductors and the location where the space is adequate for the conductors to be installed. Keep in mind that the language in 110.59 is very limited. It covers only switch enclosures over 600 volts in tunnels. The present language allows the installer more options in designing the installation. One needs to have the knowledge to calculate the cross-sectional area and fill to assure the rules of this article are complied with. I believe the Code is very clear and workable to the installers at present. ? Don Offerdahl, CMP-9
Here is also the question answered by Mike Holt himself:
Q13 Where there are two service disconnects installed on one side of the meter, can I run the service conductors through one disconnect to feed the second disconnect?
A13 Yes if adequate space is provided in the first disconnect [312.8]. As long as you can meet the requirements of 312.8 you should be fine.
