What’s Wrong Here? Hint: A Close Call Indeed
Hint: A close call indeed
Scroll down to see the answer
Whew! That was a really close call. The roofer almost drove that screw right through the electrical metallic tubing (EMT). Fortunately, it only nicked the side of it.
This is what can happen when repairs are made to metal-corrugated sheet roof decking. This is also why Sec. 300.4(E) requires cables, raceways and boxes installed under these types of roof decks, to be spaced down from the deck at least 1½ in. from the lowest portion of the roof decking. An exception allows rigid metal conduit (RMC) and intermediate metal conduit (IMC) to be installed closer since the heavier walls of those conduits are less likely to be penetrated by roofing screws. Section 410.10(F) requires the same 1½ in. separation for luminaires installed under this type of roof decking. I’ve personally seen many SER feeder cables, branch circuit metal-clad (MC) cables and even MC cables used for fire alarm circuits that have gotten damaged by these screws during roofing repairs where the wiring methods were installed too close to the roof. Presently, Sec. 300.4(E) does not apply to fire alarm circuits since Art. 760 and particularly Sec. 760.3 makes no reference to Sec. 300.4(E). However, that may change in the 2020 Edition of the NEC. But until it becomes official, I would still heed the spacing requirements of Sec. 300.4(E).
About the Author
Russ LeBlancRuss LeBlanc
Owner
Russ started in the electrical trade as an apprentice in 1985. He worked his way up to become a Journeyman Electrician and then eventually became a Master Electrician and Licensed Construction Supervisor. In 1999 Russ become an Electrical Instructor for The Peterson School of Engineering in Massachusetts where he developed his passion for teaching, and quickly became Department Head of Electrical Instruction. Russ has taught thousands of apprentices, electricians, engineers, inspectors, and other electrical professionals during his career as an instructor. He continues to provide electrical professionals with Electrical Code seminars, Arc-Flash Awareness training seminars and educational material through his LeBlanc Consulting Services in North Reading, MA whose specialty is educating electricians. He has been an active member of the NFPA Electrical Section and has authored hundreds of National Electrical Code proposals and comments which have become Code rules to improve the safety for the electrical industry. Russ is also an IAEI certified Electrical Inspector.
Please visit www.russleblanc.net for more information.
