Code Q&A

Feb. 17, 2011

Q. Can I install 120V conductors in the same space with 277V conductors? If the answer is yes, what restrictions apply?

A. Power conductors of AC and DC systems rated 600V or less can occupy the same raceway, cable, or enclosure if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)]. Control, signal, and communications wiring must be separated from power and lighting circuits so the higher-voltage conductors do not accidentally energize the control, signal, or communications wiring.

See the following applicable sections of the Code:

CATV coaxial cable [820.133(A)]
Class 1, Class 2, and Class 3 control circuits [725.48 and 725.136(A)]
Communications circuits [800.133(A)(1)(c)]
Fire alarm circuits [760.136(A)]
Instrumentation tray cable [727.5]
Sound circuits [640.9(C)]

Class 1 circuits of Class 2 and Class 3 circuits that have been reclassified as a Class 1 circuit [725.130(A), Ex 2] can be run with associated power conductors [725.48(B)(1)] if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)].

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.