National Electrical Code

The NEC Zone System

April 17, 2018

If you are new to the Zone system, know the applicable protection methods and definitions

Articles 501, 502, and 503 of the National Electrical Code (NEC) provide the requirements for Class I, Class II, Class III locations, respectively. The Location is further identified as Division 1 (combustibles present under normal conditions) or Division 2 (combustibles present only during abnormal conditions).

The Zone system is an alternative to the Division system for Class I and II locations (Art. 505) and Class III locations (Art. 506). While the Division system has two divisions, the Zone system has three zones (0, 1, and 2 for gases or liquids; 20, 21, 22 for fibers/flyings).

The Zone system accounts for the properties of the flammable or combustible materials [Sec. 505.5(A) and Sec. 506.1(A)] and the method(s) of protection. This “customized” approach can provide an advantage for both safety and cost.

Depending upon the installation, to correctly apply the Zone system you may need to use the several standards listed in the Informational Notes identified in the first few Sections of Articles 505 or 506.

If you are new to the Zone system, know the applicable protection methods. Also, spend some time becoming familiar with the definitions before diving into the requirements.

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.