A seemingly simple change in the 2008 National Electrical Code (NEC)— prompting revisions or deletions of text for municipal, county or state NEC adoption processes relating to the installation of exposed nonmetallic-sheathed (NM) cable in a dwelling unit crawl space—has upset some people in the electrical industry. Others see the additional requirements as a safety consideration and are applauding the change. A possible compromise between the two differing positions on this issue could be achieved by a change for the 2011 NEC. A thorough understanding of the installation requirements and a brief history and intent of the NEC text in the 2005 and previous issues may help prompt a change.
The text in question is located in 334.15(C) and reads as follows (the new text is underlined): “In Unfinished Basements and Crawl Spaces. Where cable is run at angles with joists in unfinished basements and crawl spaces, it shall be permissible to secure cables not smaller than two 6 AWG or three 8 AWG conductors directly to the lower edges of the joists. Smaller cables shall be run either through bored holes in joists or on running boards.” As can be seen, the change involved just adding “and crawl spaces” to the title of the subsection and to the text in the first sentence. As stated previously, this change seems fairly simple in nature and is not very controversial. However, let’s first look at the original text and the reason it was in the NEC.
An unfinished basement is not defined in the NEC, but a basement is defined in the 2003 International Residential Code (IRC) as “that portion of a building that is partly or completely below grade.” Section R305.1 in the 2003 IRC also provides text for minimum ceiling heights for basements as follows: “Habitable rooms, hallways, corridors, bathrooms, toilet rooms, laundry rooms and basements shall have a ceiling height of not less than 7 feet (2134 mm). The required height shall be measured from the finished floor to the lowest projection from the ceiling.” There is an exception to R305.1 that applies to basements as follows: “2. Ceilings in basements without habitable spaces may project to within 6 feet, 8 inches (2032 mm) of the finished floor; and beams, girders, ducts or other obstructions may project to within 6 feet, 4 inches of the finished floor.” Notice that R305.1 does not provide a ceiling height for a crawl space. It also is interesting to note that, throughout the IRC, attics and crawl spaces are referred to within the same sections, implying that they are addressed similarly, but crawl spaces and basements are not.
Scanning older editions of the NEC, NEC handbooks and other Code-related documents where only the basement NM cabling was addressed, a common concern for an unfinished basement was expressed. The concerns seemed to focus around the storage of clothing on hangers in an unfinished basement with the possible damage that could occur to smaller sizes of NM cables directly attached to the bottom of beams, joists and other support structures. The discussion considered NM cables with two 6 AWG or three 8 AWG conductors (but not smaller cables) substantially large enough to withstand possible damage and subsequently to permit attachment of these larger NM cables directly to the bottom of joists. The explanations stated that hanging heavy clothing on smaller NM cables could cause undue strain at the support staples with possible damage to the NM cables’ internal conductors. This damage could result in a fire, so the smaller NM cables should be installed on running boards or through bored holes in the joists.
The addition of “crawl spaces” to 334.15(C) now requires NM cables smaller than two 6 AWG or three 8 AWG conductors within the cable to have running boards for the cables or have bored holes. The proposal requiring crawl spaces to comply with the same open cable rules as unfinished basements did not have any substantiation of a problem but stated “334.15(C) did not give direction as to the requirements for a crawl space and since the same dangers exist in unfinished basements and crawl spaces, this subsection should apply to both locations.” The two locations do not seem to be equal, since no one would hang their clothes in a crawl space. A crawl space would more equate to an attic area and, if protection of the NM cable were necessary, compliance with 334.23 would be more appropriate. Protection of NM cables within 6 feet of the entrance into the crawl space seems more suitable.
ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at firstname.lastname@example.org.