The National Electrical Safety Code and National Electrical Code are similar in their overall purpose and safe electrical installations. They also overlap in some respects as applied to properties and premises wiring systems. Knowing where requirements of one code end and the other begin is valuable to those performing work in jurisdictions that adopt and apply both the NESC and the NEC.
This article is intended to promote a basic understanding of the two codes, their applicability requirements, specific interests and how the NESC and NEC relate to one another. In the ever-changing electrical landscape, it’s important to understand the intent and application of each code. When it comes to working with electricity, being adequately prepared to protect lives and property could be the difference between a safe or unsafe environment.
About the two codes
The NESC is published and developed by the Institute of Electrical and Electronics Engineers. Introduced in August 1914, it is an invaluable code that is widely relied on throughout the United States.
The NEC, on the other hand, originated in 1897 and is developed and published by the National Fire Protection Association, which has been its sponsor since 1911.
The NEC and NESC are American National Standards Institute (ANSI) codes and must follow the ANSI Essential Requirements for standards development organizations.
Each code contains the minimum requirements for engineering reliable, resilient electrical systems. An important difference is that the NEC is an electrical installation code that is primarily prescriptive, while the NESC is a performance-based installation code and one that includes safe work rules for employees.
The NESC is revised every five years to provide installation requirements, safe work practices and practical guidance for safeguarding installers, operators and maintenance workers of electrical/communication supply lines and equipment employed by utilities, communications providers and railways. It is the U.S. standard for the safe installation, operation and maintenance of electric power and communication utility systems. It covers power substations, power overhead and underground transmission, and distribution power lines.
The NEC is a primarily prescriptive electrical installation code. The NESC is a performance-based installation code with work rules. It’s important to respect the difference.
The NEC is revised every three years and covers the installation of electrical conductors, equipment and raceways; signaling and communications conductors, equipment and raceways; and optical fiber cables and so forth, typically on residential, commercial or industrial properties. The NEC’s purpose is the practical safeguarding of people and property from hazards arising from the use of electricity. It is a minimum standard, and further effort may be needed for an installation to be efficient, convenient or adequate for good service or future expansion.
Neither the NESC nor the NEC are intended as merely design specifications or instruction manuals for untrained people. Industry electrical training programs, such as apprenticeships, include schooling and on-the-job training, which includes applying the electrical codes to installations and systems. Although the NESC and NEC are developed for voluntary use and mandatory adoption, local jurisdictions or utilities could also have notable mandatory code amendments or modifications. It is important for users to understand all national and local electrical codes and standards in effect in their work area. Municipalities, counties, states and local utilities may be responsible for approving installation and inspection work.
The demarcation between the two codes is the service point, differentiating the line side (covered by the NESC) and the load side for premises wiring (covered by the NEC).
The codes compared
It’s important to fully grasp each code’s scope, purpose and applications, including the point of demarcation where one must yield to the other’s jurisdiction.
NESC rules contain the basic provisions, under specified conditions, considered necessary for safeguarding the public, utility workers (employees and contractors) and utility facilities. The NESC also applies to similar electrical/communication infrastructure under the exclusive control of the utility or their authorized representatives. The purpose and scope of the NESC are provided in Sections 010 and 011, respectively.
In comparison, the scope of the NEC—as provided in Section 90.2(A) and (B)—is extensive in describing the covered electrical installations and premises wiring and what the NEC does not cover. It specifically excludes installations under the exclusive control of an electric utility in accordance with specific conditions.
Both documents undergo continuous cyclical revision processes. They are works in progress with the goal of remaining relevant and adoptable.
Service point— a moving target
The two codes do not compete with one another, but they do have some overlap. For example, both codes have requirements for outdoor overhead conductors over 1,000V and service drop clearances. The NEC and NESC also refer to the other code for necessary information. The demarcation between the two codes is the service point, differentiating the line side (covered by the NESC) and the load side for premises wiring (covered by the NEC). The service point is often established by the service utility.
The NEC’s and NESC’s scopes meet at the service point, which serves as the general basis for demarcation and jurisdictional boundary between the two codes. Typically, the service point is the electrical meter, but not always. Often a utility will install metering on the premises wiring side because it’s more adaptable.
As an example, for an across-the-line 200A serving a typical dwelling unit, the meter is often the service point. Similarly, in an underground service, the service lateral may be routed to the meter, which could be considered the service point.
However, in a larger service arrangement with a current transformer (CT) enclosure for metering, with risers that go up the building to weather heads, the service point may be located at the service drop termination to the conductors that exit the weather heads. In another example, remote metering might involve installing a CT on a pole remote from the service equipment. In all three examples, metering or the metering equipment typically influences where the service point is located. Check with the local jurisdiction and utility company to determine the exact location. It is a variable and moving target. Many installation examples can be provided to demonstrate how a service point’s location can move around and often further up the street to the substation or point of generation.
Gaps and opportunities
In some jurisdictions, as the service point moves up the street closer to the generating station, owners sometimes inherit overhead distribution systems that were originally constructed to NESC requirements. This can present significant challenges for facility owners and jurisdictional inspectors that must now occasionally apply the NEC to those systems. There is a need to fill this gap with the recognition of existing medium- and high-voltage systems that were constructed to the applicable NESC requirements but that are now privately owned due to a relocated service point.
Standardized voltage classifications
An opportunity also exists in the NESC and the NEC relative to establishing standardized voltage classes and terminology used among electrical codes. The NESC covers higher voltage systems such as transmission lines, substations and other facilities with an extremely high-voltage electrical output. Currently, the terms low-, medium- and high-voltage are used within these codes.
The NEC generally addresses this by referencing either greater or less than 1,000V, without system voltage classifications. The NESC appears to address voltage classes as low, medium, high and extra high up through 800 kilovolts (kV). ANSI C84. 1-2020, American National Standard for Electric Power Systems and Equipment—Voltage Ratings (60 Hertz), establishes system voltage classes.
This standard provides a better understanding of voltages associated with power systems and equipment use by establishing nominal voltage ratings and operating tolerances for 60-Hertz electric power systems above 100V. The service voltage is usually limited to those voltages the serving utility provides.
Effective use and application of the NESC and NEC can help improve joint-use work between utilities and provide clear guidance for regulators. There are large-scale renewable systems including solar farms, wind generation facilities and energy-storage systems being installed and used within the NESC-NEC jurisdictions on both sides of the service point. Communication and collaboration are essential so that all entities can get it right when it comes to effectively applying these electrical codes.
|Low Voltage||Medium Voltage||High Voltage||Extra-High Voltage||Ultra-High Voltage|
Nominal system voltages 1,000V (1 kV) or less
Nominal system voltages greater than 1 kV but less than 100 kV
Nominal system voltages greater than 100 kV and equal to or less than 230 kV
Nominal system voltages greater than 230 kV and equal to or less than 1,000 kV
Nominal system voltages equal to or greater than 1,000 kV