Code Q&A: Conductor Limitations in Wireways

Nov. 20, 2018

Check your knowledge of wireway and the National Electrical Code.

Q. What is the NEC limit on the number of conductors and cables that can be installed in a wireway?

See the answer below.

This answer is based on the 2017 NEC. Underline text indicates a Code change.

A. The maximum number of conductors or cables permitted in a wireway is limited to 20% of the cross‑sectional area of the wireway [Sec. 376.22(A)].

Splices and taps must not fill more than 75% of the wiring space at any cross section [Sec. 376.56].

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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.