This column marks the start of the second year for “Current Affairs.” In reviewing covered material and subjects for the next year’s worth of columns, I realized that we failed to cover one topic that is fundamental to facility electrical systems: the National Electrical Code, or NEC. While I know hvacr engineers are aware of the NEC as a standard for electrical work, its proper role may not always be fully understood.

A National Standard

The NEC is produced and distributed by the National Fire Protection Association (NFPA). Like all NFPA codes, it is a consensus standard, meaning that it is developed, interpreted, and updated by committees of individuals representing all interest groups. Representation on code-making panels includes manufacturers, contractors, insurers, engineers, and enforcement officials.

The NEC is adopted as law by most jurisdictions, as perhaps the most universally applied building code in the nation, and is adopted by OSHA as applicable to all employee workplaces. It applies to installation of electrical conductors and equipment in or on almost all public and private buildings and structures. It is easier to list the few categories that are outside its scope than to comprehensively describe its jurisdiction. Ships, automobiles, aircraft, and other transportation vehicles; railroads; mines; and facilities of electric and communications utilities are exempt from the requirements of the NEC (although all are covered by other safety standards).

Safety First and Last

Article 90, the introduction to the NEC, states, “The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.” This is the sole purpose of the NEC; compliance should result in a hazard-free installation, but not necessarily efficient, convenient, or adequate electrical service.

The safety of an electrical installation involves not only the initial conditions of the installation, but the maintenance and future use of it as well. The construction of an electrical system must clearly protect persons from accidental contact with energized parts and reduce the risk of fire from overheated or failed components. However, it must also be capable of being maintained to keep it in proper, safe operating condition, without exposure of maintenance personnel to undue hazards. Finally, if the system does not provide some margin for future growth in electrical usage within the facility, it is likely to become overloaded and present a fire hazard.

Not a Design Manual

To address these multiple aspects of safety, the NEC includes not only construction requirements, but also design-related requirements including conductor ratings, equipment sizing criteria, fuse and circuit breaker selection criteria, and requirements for maintenance access to electrical equipment. This wealth of detailed data frequently leads people to assume that the code contains all the information necessary to design an electrical system, or that a system that “meets the code” is all they need for their facility.

This is not the case. While admittedly complex and detailed, the intent of all the information in the code remains safety. Many aspects of electrical system design that impact efficiency, reliability, and quality of electrical service are not addressed, and while a good design must always comply with the code, compliance does not ensure a good design. The NEC should always be considered a set of minimum requirements that may need to be exceeded to meet the design objective.

Unfortunately, ill-informed owners attempting to “value-engineer” cost out of projects are not alone in this misconception. In too many cases, electrical contractors who should understand the proper application and limits of the NEC propose design changes or material substitutions with the justification: “That’s all the code requires.” I’ve even had cases in which field observation of an installed project turned up deviations from the design for which the contractor explained he had received approval from the electrical inspector. This results in a careful explanation (that should be unnecessary) that while the inspector has the authority to interpret and enforce the code, the design intent may be to go beyond the requirements of the code and cannot be changed without the engineer’s authorization.

The “Utility” Exemption

Most utility facilities are outside of the scope of the NEC, but the actual language of this exemption is important. The NEC does not cover “installations … under the exclusive control of electric utilities for the purpose of communications, metering, generation, control, transformation, transmission, or distribution of electric energy.” The important issues are control of the facilities and their use. The intent is to exempt only those facilities that are designed, operated, and maintained by qualified personnel under the requirements of the utility safety standard, the National Electrical Safety Code (NESC).

Consequently, a generation plant and substation that is part of a co-generation installation on a college campus or in a medical center, although used for utility-type generation and distribution of electric energy, must comply with the NEC unless it is actually run by the utility company. Similarly, the NEC covers an administrative office building even though it is owned and maintained by the utility. ES