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National Electrical Code

The NEC and Art. 725: Circuits — Part 3

Oct. 20, 2020

Highlights of Part III that covers Class 2 and Class 3 circuits

Part III of Art. 725 covers Class 2 and Class 3 circuits. Each is that portion of the circuit between a Class 2 or Class 3 power source and the connected load. What are these power sources?

A listed Class 2 or Class 3 transformer.
A listed Class 2 or Class 3 power supply.
Other listed equipment marked to identify the Class 2 or Class 3 power source.

You can look at the power source characteristics in Chapter 9. Table 11(A) is for AC circuits, and Table 11(B) is for DC circuits. These tables and their associated notes take up a full page.

Highlights include:

You can’t parallel the outputs of Class 2 or Class 3 power sources unless they are listed for that interconnection [725.121(B)].
Install supply-side conductors per the applicable requirements of Chapters 1 through 4 [725.127].
Choose load-side conductors that meet the application, as laid out in 725.179 and Table 725.179(J). For example, use CL2P for Class 2 plenum applications and CL3R for Class 3 riser applications [725.130(B)].

About the Author

Mark Lamendola

Mark is an expert in maintenance management, having racked up an impressive track record during his time working in the field. He also has extensive knowledge of, and practical expertise with, the National Electrical Code (NEC). Through his consulting business, he provides articles and training materials on electrical topics, specializing in making difficult subjects easy to understand and focusing on the practical aspects of electrical work.

Prior to starting his own business, Mark served as the Technical Editor on EC&M for six years, worked three years in nuclear maintenance, six years as a contract project engineer/project manager, three years as a systems engineer, and three years in plant maintenance management.

Mark earned an AAS degree from Rock Valley College, a BSEET from Columbia Pacific University, and an MBA from Lake Erie College. He’s also completed several related certifications over the years and even was formerly licensed as a Master Electrician. He is a Senior Member of the IEEE and past Chairman of the Kansas City Chapters of both the IEEE and the IEEE Computer Society. Mark also served as the program director for, a board member of, and webmaster of, the Midwest Chapter of the 7x24 Exchange. He has also held memberships with the following organizations: NETA, NFPA, International Association of Webmasters, and Institute of Certified Professional Managers.