National Electrical Code

Chapter 9 of the NEC — Part 7

April 19, 2021

Tables at the end of Chapter 9 help when working with Art. 760.

Chapter 9 of the National Electrical Code (NEC) ends with a series of related tables:

11(A). Class 2 and Class 3 Alternating Current Power Source Limitations.
11(B). Class 2 and Class 3 Direct Current Power Source Limitations.
12(A). Power Limited Fire Alarm (PLFA) Alternating Current Power Source Limitations.
12(B). Power Limited Fire Alarm (PLFA) Direct Current Power Source Limitations.

When working with Art. 760, Part III, these are often helpful.

Inherently limited power supplies do not need overcurrent protection; that is often a reason to choose them. Suppose you have a 24VAC power supply inherently limited to 8A and its nameplate rating is 90A. Can you use it for your application that calls for a PLFA source? From Table 12(A), the answer is yes. What if your application calls for a Class 3 power supply? No, because Table 11(A) requires one over 30V.

In some cells, you see a figure such as 100/V_MAX.. To know the quantity this represents, divide the numerator (top number) by the maximum voltage of the power supply. If the power supply maximum voltage is 50V, then 100/V_MAX is 2.

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.