Cutting Edge of Technology?

Electrical construction has always been a dangerous profession, so finding ways to make the work less hazardous is certainly the goal of the National Electrical Code (NEC); Underwriters Laboratories; the Occupational Safety and Health Administration; NFPA 70E, the Standard for Electrical Safety in the Workplace; the National Electrical Manufacturers Association; the National Electrical Contractors Association; and others within the electrical industry.

Sharp edges on metal boxes, panelboard and switchboard enclosures, luminaires and other similar electrical equipment are a concern of all in the electrical industry; however, the UL product standards, rather than the NEC, more appropriately deal with sharp edges on electrical equipment. UL Standards, such as the Standard for Sharpness of Edges on Equipment (UL 1439), addresses these issues at the manufacturer and listing level. A review of this issue may provide some assurances to the electrical industry that sharp edges on electrical equipment are adequately covered, so proposals to the NEC to require panelboards, switchboards, metal boxes and other electrical equipment to comply with sharp-edge requirements are unnecessary.

During the 2008 NEC process, Panel 9 rejected a proposal dealing with sharp edges on metal pull and junction boxes at the proposal stage and then accepted a comment dealing with the same subject but expanded the coverage in new Section 312.10(B) in Article 408 covering switchboard and panelboard enclosure edges as well as metal pull and junction box edges as a new subsection 314.40(D). The suggested new text in the Comment was as follows: “312.10(B) Enclosure Edges. All sharp edges of metal enclosures within the scope of this article that are subject to hand contact during customary installation activity shall, at the time of manufacture, be protected or shall be de-burred and rounded to minimize the risk of injury. This requirement shall take effect January 1, 2011.

“314.40(D) Enclosure Edges. All sharp edges of metal pull and junction boxes over 1,650 cm3 (100 in.3) in size that are subject to hand contact during customary installation activity shall, at the time of manufacture, be protected or shall be de-burred and rounded to minimize the risk of injury. This requirement shall take effect January 1, 2011.”

The NEC Technical Correlating Committee reported this comment as “reject” since the comment text contained unenforceable and vague terminology, such as “during customary installation activity…” and “at the time of manufacture, be protected…” so the proposed text was not included as new text for the 2008 NEC.

The original substantiation for the proposal and the comment accepted at the comment stage of the process for the 2008 NEC provided only anecdotal information that sharp corners and edges on enclosures have “caused thousands of injuries and thousands of hours of lost time” and “could lead to a fatal shock or serious cut due to jerk reaction.”

For the 2011 NEC, a proposal was submitted to again add 312.10(B) with an additional proposal to add 314.40(D), both providing similar language about sharp edges as the text submitted during the 2008 comment stage but without an effective date. The proposals for the 2011 NEC did not have anecdotal information or any technical substantiation to justify adding the text to the NEC.

Both proposals had eight members of the panel voting affirmative and four members voting negative. The affirmative votes on this issue stated, “Although the issues raised in this proposal are frequently reserved for product standards, the NEC does enter this arena if the product standards consistently fail to adequately address a safety concern.” The negative statements noted “requirements exist in the Standards, and members of the Panel were encouraged to participate in the standards process if they believed requirements were in need of revision. As a result of discussions during the last Code cycle, all members were extended an invitation to join Standards Technical Panels and encouraged to file field complaints so problems could be identified and addressed. No field complaints related to this issue were filed.”

During the 2011 NEC comment stage, comments were submitted with substantiation that UL 50, the standard covering enclosures, already contains the following text: “An edge on an enclosure shall not be sufficiently sharp to constitute a risk of injury in normal maintenance or use.” One submitter stated “there has been no comprehensive data or statistics provided to demonstrate exactly what problem is being fixed. Scrapes, scratches and cuts occur for many reasons on a construction site. Even plastic edges can take the skin off a knuckle if hit at the right angle. Interestingly, most electrical contractors we talk to focus on luminaire housings as the most significant source of edges—not cabinets or cutout boxes.”
Changes suggested for sharp edges were rejected, so this issue again will not be covered in the 2011 NEC.

ODE is a staff engineering associate at Underwriters Laboratories Inc., based in Peoria, Ariz. He can be reached at 919.949.2576 and

About the Author

Mark C. Ode

Fire/Life Safety Columnist and Code Contributor
Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and .

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