Hint: Close call
If the screw penetrating the roof was just one inch to the left, it could have created a shocking situation. This electrical metallic tubing (EMT) is installed too close to the metal roof decking. The reason Sec. 300.4(E) was added to the Code was to prevent wire damage from happening in situations just like this. Section 300.4(E) requires raceways, cables, and boxes to be spaced at least 1½ in. from the lowest portion of the metal-corrugated sheet roof decking. Roofers tend to use extra-long screws when making repairs to the roof. These self-tapping screws can easily penetrate wiring methods installed too close to the roof. Exception No. 1 in Sec. 300.4(E) permits rigid metal conduit (RMC) or intermediate metal conduit (IMC) to be installed without the 1½ in. spacing. For the 2023 Code, Exception No. 2 was added to remove the 1½ in. spacing for roof decking where a concrete slab of 2 in. or more in thickness is installed on top of the roof. Section 410.10(F) has very similar rules for luminaires installed under roof decking.
About the Author
Russ 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.