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How do I know if a switchboard or panelboard is Listed for top or bottom feed or both?

Posted By Underwriters Laboratories, Saturday, March 01, 2008
Updated: Friday, February 08, 2013

Question: Switchboard

How do I know if a switchboard or panelboard is Listed for top or bottom feed or both?

Answer

Switchboards are Listed under the category Deadfront Switchboards (WEVZ), located on page 325 in the 2007 UL White Book. This information can also be located using UL’s Online Certification Directory at http://www.ul.com/database by entering "WEVZ” at the UL Category Code Search. The Deadfront Switchboard Marking Guide, located in Appendix A of the 2007 UL White Book, provides additional details regarding conduit entry/exit points. Specifically, on page 17 of the marking guide, under the heading "Conduit Entry,” the publication states, "UL evaluates switchboards to determine compliance for the clearance of conductors and conduit entering into the bottom of a switchboard, per NEC 408.5. Acceptability of other conduit entry/exit points can only be determined at the time of installation.” As also noted in this section of the marking guide, other entry points have been evaluated by UL "…if instructions and drawings showing the intended conduit or raceway locations are (1) supplied with the switchboard section or enclosure or (2) contained in the manufacturer’s catalog (identified by the catalog number or other designation that appears on the switchboard).

Panelboards, including "Enclosed Panelboards”, are Listed under the product category Panelboards (QEUY), located on page 251 in the 2007 UL White Book. This information can also be located using UL’s Online Certification Directory atwww.ul.com/databaseby entering "QEUY” at the UL Category Code Search. As noted in the guide information: "Only panelboards marked to indicate that they are for use in specific enclosures (identified by either catalog number or specific dimensional information) and panelboards labeled as "Enclosed Panelboards” have been investigated to determine that wiring space is adequate.” With respect to this statement, it should be noted that wire-bending space for Listed "Enclosed Panelboards” is evaluated to ensure compliance withNEC408.55. ThisCodesection defines the required top, bottom, and side wire-bending space for the enclosure of a panelboard. All enclosed panelboards, including those without a factory provided hole or knockout (or other provision for connection of a wiring system), would be required to comply with these basic requirements.

Conduit entry and exit points, such as holes, knockouts, or other provisions for connection of a wiring system, in panelboard enclosures have only been evaluated by UL where they are factory-supplied. Any field punched knockouts have to be evaluated by the AHJ in the field for suitability of wire bending space, maintenance of an environmental rating on the enclosure, spacings to live parts, etc. If a product is factory supplied with knockouts on the bottom or the side for a bottom or side entry and the installer punches a hole for conduits in the top, it is up to the AHJ to evaluate the suitability of that modification to the enclosure.

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Tags:  March-April 2008  UL Question Corner 

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