Affecting Wire & Cable Products
Raceways and wet locations, NEC Sections 300.5(B) and 300.9
The inside of a conduit installed in a wet location is to be considered a wet location. This sounds redundant but many people believe the inside of a conduit should be considered a dry environment. The 2008 NEC Section 300.5(B) now clearly states that underground raceways are considered a wet location that require conductors rated for wet locations. The NEC has also added new wording to this section that helps to clarify that cables installed under a building shall be in a raceway, even if they are rated for direct burial.
Section 300.9 also addresses raceways. It states that where raceways are installed in wet locations above ground, the interior of the raceway shall also be considered a wet location, again requiring conductors listed for wet locations.
Conduits installed on rooftops, NEC Section 310.15(B)(2)(c)
Rooftop de-rating adjustment temperatures for conduits installed on rooftops exposed to sunlight are now required to be derated in addition to the ambient air temperature above the roof. Due to solar radiation, the inside of the conduit gets much hotter than the surrounding air temperature. The actual temperature rise was shown in a report published by the Copper Development Association (CDA) after extensive field studies. Information on this study can be found at www.copper.org under building wire applications.
Service and feeder conductors for dwellings, NEC Table 310.15(B)(6)
Services and feeders for dwellings are allowed to use smaller service and feeder conductors than industrial and commercial loads due to single phase dwelling loads being much smaller than the rating of the panel board.. The table can no longer be used for feeders to multiple subpanels. The table is now only be used for the main power service or feeder that supplies either by the branch circuits, or feeders or both, all loads that are associated with the dwelling unit.
Type MC Cable in wet locations, NEC Section 330.10(A)
Type MC Cables with interlocked armor are now required to include a jacket when used in wet locations. NEC Section 330.10(A) requires that interlocked armored cables used in wet locations have conductors listed for wet locations and a jacket over the armor. This has long been recommended by manufacturers and is now a Code requirement. Type FMC (Flexible Metal Conduit) is another product that no longer is allowed in wet locations. NEC Section 348.12 clearly states that FMC shall not be used in wet locations.
Type NM-B cable, NEC Section 334.80
Type NM-B cable is required to be derated when more than two cables are installed bundled together. NEC Section 334.80 specifically states that Type NM-B cable’s ampacity shall be derated when more than two NM-B cables are installed in thermal insulation without maintained spacing between the cables. This change was based on CDA studies of NM-B cable installed in walls with various thermal insulations. The study showed that without spacing the conductors, temperatures exceeded the maximum operating temperature of NM-B cable. This requirement is in addition to the 2005 NEC requirement for the derating of more than two cables installed through a draft stopped hole.
Type SEU and SER cables, NEC Section 338.12
Type SEU and SER Cables are not allowed to be installed underground. This 2008 NEC change supports the uses stated in the UL Guide Information for Electrical Equipment. NEC Section 338.12 now clearly states that Type SE Cables (SEU and SER) are not to be used underground with or without a raceway. Only, Type USE cable should be used for these types of installations.
It should be noted that there was much debate on the allowance for 5 kV non-shielded cables that were removed from the 2005 NEC. The 2008 NEC continues to have the 2,400 volts as maximum voltage for non-shielded cables. Industrial’s need to confirm that equipment operating over 2,400 volts has enough room to terminate shielded cable.
Most standard wiring practices are unchanged. This flyer is simply an overview of items that directly impact wire and cable. This article does not cover all changes because many of the new changes only clarify rules that are already a part of the Code.
By Dave Mercier, Director, Codes & Standards/Technical Support, has been serving on various Code Making Panels with fellow industry professionals for over ten years. He is currently serving on Code Making Panel 7 which is responsible for NEC articles that cover the use of electrical cables for general wiring.