My last article provided a history and background on Article 400, dealing with flexible cords and cables. This month, I delve further into whether flexible cords and cables could or should be installed in concealed locations. Does the National Electrical Code (NEC) already permit concealed installations, and, if so, why are these applications acceptable while others are not? Is it time to relax the rules on concealment of flexible cords and flexible cables, or should the NEC maintain these restrictions? These questions are not easy to answer and may require further study on a national level; however, I can help you understand the issues.
Let’s first look at the NEC requirements for restricting flexible cords and flexible cables. Section 400.8(1) does not permit flexible cords and cables to be used as a substitute for permanent wiring of a structure. Staples can damage flexible cords and fastenings, so 400.8(4) does not permit these cables or cords to be attached to building surfaces. The outside jacket of the cord or cable—and thus the interior insulated conductors in the cable or cord, unless constructed as hard or extra-hard usage cables—can be damaged by sharp edges of holes drilled in 2-by-4 wooden studs or by metal framing members. For that reason, 400.8(2) does not permit flexible cords and cables to be installed through holes in walls, structural ceilings, suspended ceilings, dropped ceilings or floors. Wiring methods in Chapter 3 of the NEC are much more appropriate for use as building-wiring methods because they are tested while listed for that use; flexible cords and cables are not.
Flexible cords and cables cannot be used where concealed by walls, floors or ceilings or where located above suspended or dropped ceilings based on the limitations provided in 400.8(5). The purpose of this requirement is to limit the indiscriminate use and undetermined length of flexible cords and cables in these concealed locations. The limitations for flexible cords and cables concealed in dropped and suspended ceilings were inserted by Proposal 6-128 and Comment 6-75 in the 1999 NEC process. The substantiation in the proposal, which was accepted by Code-Making Panel 6 for restricting this application, was the possibility that damage or fatigue to the cable could not be readily detected since the cable would be located out of sight behind the ceiling tiles. Of course, if the dropped ceiling was constructed of metal and drywall and did not permit accessibility, the issue would be irrelevant since 400.8(1) would not permit flexible cords and cables to be used as a substitute for fixed wiring.
Another issue is why flexible cords and cables cannot be installed in raceways, unless permitted elsewhere in the NEC. Research indicates a proposal submitted for the 1999 NEC would have permitted flexible cords “to be installed in raceways where its calculated ampacity has been further derated by a factor of 0.8 or where its ampacity has been calculated under Section 310.15(b).” The Code-Making Panel 6 statement of rejection for this concept was that “conductors of flexible cords are not anticipated to be permanently installed in raceways. The requirements for portable cords are generally less stringent than for permanent wiring because portable cords are not expected to have the same life or duty cycle compared to permanent wiring which is expected to last a comparative longer time. The submitter of the proposal also did not provide any substantiation for the 0.8 that was in the recommendation.”
The last restriction for flexible cords and cables is located in 400.8(7) and does not permit installation of flexible cords and cables where subject to physical damage. Some flexible cords and cables are listed for hard usage or extra-hard usage and are tested to determine if the flexible cords and cables can withstand more physical abuse or damage. The problem is in determining how much abuse and damage is acceptable for these cords and cables, and it becomes more of a judgment call for the installer, user or authority having jurisdiction.
Even where flexible cords are permitted to be installed behind appliances, such as in 422.16(B)(2)(2) for dishwashers, these flexible cords are not subject to physical damage and are sized based on the manufacturer’s installation instructions and the rated ampacity provided on the nameplate. Obviously, more study is needed to determine if changes should be made.