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Code Q&A: Protection Options for Type NM Cable

July 18, 2018
What does the Code require when installing Type NM cable for exposed work?

Q. What does the Code require when installing Type NM cable for exposed work?

 See the answer below.

This answer is based on the 2017 NEC.

A. Exposed Type NM cable must closely follow the surface of the building [Sec. 334.15(A)]. Nonmetallic-sheathed cable must be protected from physical damage by rigid metal conduit (RMC), intermediate metal conduit (IMC), Schedule 80 PVC conduit, Type RTRC-XW conduit, electrical metallic tubing (EMT), guard strips, or other means approved by the authority having jurisdiction (AHJ) [334.15(B)].

When installed within a raceway, the cable must be protected from abrasion by a fitting installed on the end of the raceway [Sec. 300.15(C)].

Type NMC cable installed in shallow chases in masonry, concrete, or adobe, must be protected against nails or screws by a steel plate not less than 1⁄16 in. thick [Sec. 300.4(F)] and covered with plaster, adobe, or similar finish.

If Type NM cable is installed in a metal raceway, the raceway isn’t required to be connected to an equipment grounding conductor (EGC) [Sec. 250.86, Exception No. 2 and Sec. 300.12, Exception].

If Type NM cable is installed at angles with joists in unfinished basements and crawl spaces, it’s permissible to secure cables containing conductors not smaller than two 6 AWG or three 8 AWG conductors directly to the lower edges of the joists. Smaller cables must be installed through bored holes in joists or on running boards.

Type NM cable installed on a wall of an unfinished basement or crawl space subject to physical damage must be protected in accordance with Sec. 300.4, or be installed within a raceway with a nonmetallic bushing or adapter at the point where the cable enters the raceway, and the NM cable must be secured within 12 in. of the point where the cable enters the raceway.

These materials are provided to us by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visit www.mikeholt.com/code.

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.

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