Chapter 9 Nec Part 3 Mro 2 16 21 602be48040152

National Electrical Code

Chapter 9 of the NEC — Part 3

Feb. 16, 2021

Use Table 5 to help calculate the fill percentage.

Suppose you have a mix of various conductors you intend to pull in one raceway. How can you calculate the fill percentage without getting out a micrometer to determine the thickness of each type of conductor? The good news is that there’s an app for that (several apps, actually).

If your phone battery is dead or you don’t have a raceway fill calculator app, but you have a copy of the NEC, there’s still good news. You can use Table 5 in Chapter 9 to find the dimensions of each type of conductor you plan to use. Once you add up the totals for 6 of X conductor, 3 of Y conductor, and so forth, you have the total fill.

Then, you refer to Table 1 of Chapter 9 and see the maximum fill for more than two conductors is 40%. If you take that earlier total and divide it by 40%, you will have the minimum ID for the type of raceway you intend to use. Now, go to Table 4, find your raceway, and see what size you need.

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.