Code Q&A: Conductor Size for Class 1 Circuits

Your most pressing National Electrical Code (NEC) questions answered

Dec. 19, 2013

Q. What is the smallest conductor allowed by the NEC for Class 1 control and signal circuits?

A. Conductors of sizes 18 AWG and 16 AWG installed in a raceway, enclosure, or listed cable are permitted for Class 1 circuit conductors if they don’t supply a load that exceeds the ampacities specified in Table 402.5. Conductors of 14 AWG and larger must not supply loads greater than the ampacities given in 310.15 [725.49(A)]. In addition, Class 1 circuit conductors must have a 600V insulation rating and comply with Table 310.104. Conductor insulation for sizes 18 AWG and 16 AWG must comply with Table 402.3 [725.49(B)].

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.