National Electrical Code

The NEC and Branch-Circuit Ratings — Part 2

Dec. 21, 2021

Overcurrent devices must comply with these rating requirements.

Once you know the ampacity of the branch-circuit conductors [210.19] that the overcurrent device (OCPD) is protecting, you can determine the size of the OCPD [210.20]. The rating or setting of the OCPD must comply with these four requirements:

If the circuit supplies any continuous load(s), the rating of the OCPD must be at least the sum of two quantities (notice, “or setting” is not included here). The first quantity is the total non-continuous load. The second quantity is the total continuous load times 1.25 [221.20(A)]. The exception note to this requirement allows the OCPD rating to be less than that sum if the assembly, including the branch OCPD, is listed for operation at 100% of its rating. You must protect flexible cords and fixtures per 240.5.
The conductors must be protected per 240.4 [221.20(B)]. That’s an extensive text that includes a reference to 310.14 and a table of specific conductor applications. When you turn to 310.14, you read that you can use the tables in 310.15 to determine the conductor ampacity. This isn’t as “bounce me around” as it might seem. If your load is X and your conductor is Y, find the table with your conductor and then find the lowest ampacity that exceeds your load.
The rating or setting of the OCPD cannot exceed what’s specified in the applicable article referenced in Table 240.3 for equipment [221.20(C)]. The list of equipment covered by that table is long. It includes receptacles, x-ray machines, fire pumps, and busways, just to name a few.
The rating or setting of the OCPD cannot exceed what’s specified in 210.21 for outlet devices [221.20(D)]. Outlet devices are categorized as either lamp holders [210.21(A)] or receptacles [210.21(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.