Ecmweb 8423 Thinkstockphotos 543468258
Ecmweb 8423 Thinkstockphotos 543468258
Ecmweb 8423 Thinkstockphotos 543468258
Ecmweb 8423 Thinkstockphotos 543468258
Ecmweb 8423 Thinkstockphotos 543468258

Tip of the Week: Calculating Loads for a Store Building Using Annex D in NFPA 70 (NEC)

Sept. 6, 2016
Example D3 of this annex may be used as a guide for just about any commercial installation. 

What can you learn from the NEC’s Annex D, Example D3? The title of the example is “Store Building,” and that means it’s for a commercial installation (rather than industrial or residential).

You may use this example as a guide for just about any commercial installation. Your application may not have this example’s show window lighting load or outside sign circuit, but it may have other loads you can replace those with. Or take your typical office load; it’s basically lights and receptacles, and you can use this example as a guide (of course, you don’t need the show window lighting).

The first step shown in all of the Annex D examples is to characterize the loads. In this example, we see two simple lists:

1. Noncontinuous loads. These are classified as loads that run three hours or less.

2. Continuous loads. These are classified as loads that run more than three hours.

In each list, the load name and value are shown as a line entry. Adding those loads gives you the total for each list.

Article 220 provides the requirements for calculating branch-circuit, feeder, and service loads. Part II of that Article is for branch-circuits. In Part II, Sec. 220.12 refers us to Table 220.12. That Table lists general lighting loads by occupancy. This occupancy is a store, and thus is listed in this Table. The unit load is 3VA per square foot.

Going back to our example, there’s an asterisked note below the two lists of loads. That note explains why, with these load values, you must use the value from Table 220.12.

Now if you had just sat down to do this job and you hadn’t done one like it previously, you might have missed that requirement to use the value from Table 220.12. For at least the first few times you do a particular application, walking through the Annex D example is a good way to avoid making mistakes.

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.

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