Code Q&A: Conductors Installed in Parallel

March 8, 2018

NEC requirements for conductors installed in parallel

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Q. What does the Code require for separate raceways or cables that contain parallel conductors?

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This answer is based on the 2017 NEC.

A. Separate raceways or cables containing parallel conductors must have the same electrical characteristics [310.10(H)(3)], as shown in the Figure.

If one set of parallel conductors is installed in a metal raceway and the other conductors are installed in PVC conduit, the conductors in the metal raceway will have an increased opposition to current flow (impedance) as compared to the conductors in the nonmetallic raceway. This results in an unbalanced distribution of current between the parallel conductors.

Parallel conductor sets must have all circuit conductors within the same raceway [Sec. 300.3(B)(1)].

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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.