Concepts of the NEC: Safety and Efficient Design


Concepts of the NEC: Safety & Efficient Design

11.Blurb 11_Alabama

Concepts of the NEC is one of our topics at next month's Engineering Societies of Alabama and Mississippi's summer meeting on June 10-12th in Biloxi, Mississippi.

The NEC has dual purposes of safety and cost/resource effective design. To summarize: (1) safety concerns (avoid underdesign) and (2) efficient design concerns (avoid overdesign).

Underdesign. As electrical professionals, we are familiar with safety concerns...don't underdesign a power distribution system due to concerns over potential electrical fires. Public safety is always our first concern.

Overdesign. But the second concept, overdesign is also a key part of the NEC. For the most part, this concept is overlooked in today's electrical design. It is simply too difficult to do all of the necessary calculations to implement efficient design. Why - time constraints, looming deadlines and lack of knowledge about the NEC's requirements.

Despite our difficulty in avoiding overdesign, it is a primary concept behind all the NEC articles put together over the years since the first article was written. Right up there with the concept of safety.

To avoid overdesign and right size design a power distribution system, the NEC breaks the demand load into resistive, motor (inductive) and lighting loads. Breaking the demand load into types of loads allows for the design of an optimum power distribution system.

By just adding all the loads (kVAs) up, the demand factors offered by the NEC cannot be applied. Loads must be tracked by load type in order to reduce the connected load sum by the relevant demand load. This process is outlined in NEC Article 220 Branch Circuit, Feeder and Service Calculations. Unless this process is followed, the total load cannot be reduced so the power distribution system is overdesigned.

A threshold issue when we put together PowerCalc, was to track demand loads incorporating the NEC's demand factors as a default in the automatic calculations. The user can always override these factors, but the NEC baseline is always recognized.

What's the result of not paying attention to this mandate of the NEC?  Electrical professionals have over coppered facilities causing developers, owners and clients to get some big bills for overdesigned power distribution systems (specifying too much or oversized electrical equipment).

Electrical equipment is expensive, and clients and the world appreciate money and resources saved by not specifying unnecessary equipment. The savings are always substantial when overdesign is avoided.

So, back to Biloxi, we've touched on a few issues, but there are a lot more. For engineers who design facilities, we promise a compelling discussion. Hope to meet our colleagues and will work on a video to share with those who cannot attend.

Biloxi is an incredible place and these Engineering Societies put together a great program and have a lot of fun.

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About The Author

James Khalil, P.E. is President, Co-founder and Inventor of PowerCalc. He has 30+ years of experience at his MEP firm in Delray Beach, FL and with Carter Burgess (now Jacobs) in Fort Worth, TX; Mason & Hanger (now Zimmerman) in Lexington, KY; and Gee & Jenson (now CH2M) in West Palm Beach, FL. He received his B.S. in Electrical Engineering from the University of Texas. His experience includes projects for Saudi Arabia and Qatar; the US Departments of Energy, State, and Defense; and universities, schools, health facilities, and arts centers.