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Code Q&A: Conduit Fill Limitations

Oct. 9, 2019
Test your NEC knowledge.

Q. What is the maximum number of conductors allowed by the Code to be installed in rigid metal conduit (RMC)?

See the answer below.

A. Raceways must be large enough to permit the installation and removal of conductors without damaging the conductor’s insulation. When all conductors within a raceway are the same size and insulation, the number of conductors permitted can be found in Annex C for the raceway type [Sec. 344.22].

Example: How many 8 THHN conductors can be installed in trade size 1½ in. RMC?

Answer: 22 conductors [Annex C, Table C.9]

Cables can be installed in RMC, if the number of cables doesn’t exceed the allowable percentage fill specified in Table 1, Chapter 9.

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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