Code Calculations

Art. 340 covers the use, installation, and construction specifications of service-entrance cable (Types SE and USE). Type SE cable has a flame-retardant, moisture-resistant covering. Type USE cable, identified for underground use, has a ...

Mike Holt

Aug. 9, 2004

When using Type SE service-entrance cable for interior branch circuits and feeders, you must comply with the installation requirements of Parts I and II for NM cable, but not the 60°C conductor ampacity limitations noted in 334.80. The Code does not allow you to use Type USE cable for interior installations because it is not listed for this application.

The requirements of 424.3(B) requires the branch-circuit conductor for electric space heating equipment to have an ampacity of not less than 125% of the total heating load. A 10kW heater with a 3A blower motor must be wired with a conductor that has an ampacity of at least 56A. See the calculation noted in the Figure. You could use 4 AWG NM cable or 6 AWG SE cable to serve this load.

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.