All references are based on the 2020 edition of the NEC.
Installed in Harm’s Way
Securing electrical metallic tubing (EMT) raceways directly to the bottom of metal-corrugated sheet roof decking is a violation of Sec. 300.4(E). Raceways, cables, and boxes installed beneath this type of roof decking must be installed and supported in a manner that provides at least 1½ in. of space between the lowest surface of the roof decking and the top of the raceway, cable, or box. Section 410.10(F) additionally requires luminaires installed beneath this type of roof decking to be installed and supported so there is at least 1½ in. between the lowest surface of the roof decking and the top of the luminaire. This 1½ in. spacing is needed to reduce the likelihood of damage to the wiring methods and equipment, which can be caused by the long screws roofers use to make repairs to this type of roofing. I have seen many instances where those long roofing screws have penetrated directly into raceways or cables, causing massive damage to the wiring. Rigid metal conduit (RMC) and intermediate metal conduit (IMC) are two wiring methods that are permitted to be installed without the 1½ in. spacing from the roof decking.
A Scary Discovery in the Attic
I spotted this scary wiring while I was crawling around in a customer’s attic trying to snake some cables down to the basement. I was hoping to find some space for snaking my cables near the chimney. Instead, I discovered this mess of NM cables strewn everywhere. For NM cables installed in accessible attics, Sec. 334.23 requires compliance with Sec. 320.23. Where cables are run across the top of floor joists or within 7 ft of the floor joists across the face of rafters or studding, guard strips at least as high as the cable must be installed to protect the cables. For attics accessible only by portable ladders or stairs (rather than permanently installed ladders or stairs) this protection is only required within 6 ft of the nearest edge of the scuttle hole or attic entrance. We may be able to debate whether these sections of the Code are applicable here because these cables are run on top of the flooring rather than on top of the floor joists, but I don’t think there’s any questioning the applicability of Sec. 300.4, which requires these cables to be protected where subject to physical damage. Where NM cable is run exposed, Sec. 334.15(B) requires RMC, IMC, RTRC-XW, Schedule 80 PVC conduit, EMT, or other approved means of protection for the NM cables (where necessary). The lack of any securing and supporting of the NM cables is a violation of Sec. 334.30.
