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Monday, December 11, 2017
Question:
Re: CQD answer published Thursday, November 30, 2017 -Cabinets Used as Junction Boxes
1) Great service you and NECA provide the electrical industry. I have dealt with the issue of using an old panel enclosure as a junction box. I was asked to replace an old Square D Type MO panel with a Square D Type QO panel by mounting it to the front to the MO enclosure and using the MO interior as a junction box. The issue here revolves around the listing of the enclosure. Is a panel enclosure listed as a junction box after the interior is removed? The electrical inspector in Dallas only allows this in residential, single family locations. I solved this access issue many years ago when replacing an old Square D, 3-phase, 208Y/120 volt Type MO, 200 amp panel with a Square D type QO panel. The QO interior fit inside the MO enclosure and the top studs in the MO enclosure matched the mounting holes in the QO interior. The issue was the QO interior was 5-inches too short to connect to the MO studs. I bolted the bottom mounting holes to the enclosure and welded a blank to the bottom of the trim. Interestingly, the MO trim fit perfectly with the QO breakers. I was still working as an electrician and did not consider the UL listing issue. As an engineer, I am able to apply my electrical experience as an electrician working for NECA contractors in Houston, Texas to my engineering designs. Thanks, Rodney Welch
2) While I completely agree with your answer, there is a way to install a new panel over an existing panel and make the installation Code-compliant. We have designed an installation where a new panel is surface-mounted in front of a recessed panel, but is offset in one direction to allow access to the splices contained in the old panel. As an example, the new panel is offset to the right, such that it covers approximately 1/3 of the existing panel. Holes with bushings are provided in the back of the new panel to allow wires to pass into the old panel and then be routed into the existing conduits or be spliced with the existing wiring. A new cover is then fabricated to cover the remaining 2/3 of the existing panel. To be Code-compliant, the metal thickness of the existing panel and of the new cover must meet the minimum thickness required in Section 314 of the NEC (2014). The new cover must be constructed from the same material as the metal box or it must be lined with 1/32" thick insulating material. The volume of the existing panel must be checked to ensure it is sufficient to house the size/number of wires and splices to be contained in it. Note that fabricating a new cover for the existing panel voids the NRTL listing of that enclosure, however, Section 314.40 (2014) does not require the metal box to be listed, it only requires it to meet the minimum metal thickness. Section 314.41 (2014) requires the covers for metal boxes to meet the metal thickness OR be listed. Thus, the installation is Code-compliant by meeting the required metal thickness for both. Robert Venvertloh, PE
A
Answer:
Hey Rodney and Robert thanks for your additional comments. You have some good points and it is up to the AHJ to determine if the installation is acceptable.