Prescriptive Versus Performance Rules: Where the NEC Comes In

Good workmanship

The National Electrical Code (NEC) is primarily a prescriptive-based code, meaning it indicates requirements and not what must happen electrically. Performance rules, on the other hand, clarify what must be accomplished electrically.

For example, a prescriptive requirement in the Code could convey that a certain type of protection is required, such as Section 210.8(B), which mandates ground-fault circuit-interrupter protection for 125-volt (V), 15- and 20-ampere (A) receptacles in locations or facilities other than dwelling units. In Article 100, the informational note to the definition of “ground-fault circuit-interrupter” provides performance language that indicates the level of milliamperes at which the protection must operate.

Grounding and bonding are essential processes for electrical system installation safety. In today’s wiring systems, electrical grounding and bonding connections typically are present at electrical services and installed with feeders and branch circuits. Electrical grounding and bonding are performance functions. In Section 250.4, the NEC provides performance language that describes what grounding and bonding must accomplish. Performance-based rules in the NEC make many other prescriptive requirements easier to follow.

When an electrical system or electrical equipment is grounded, a connection to earth is implied. Without such a connection, there is no grounding (Article 100 defines “grounded” and “ground”). When electrically conductive parts are effectively bonded together, electrical continuity and conductivity are established.

Constructing an effective ground-fault current path is an important part of a grounding and bonding scheme because it is directly related to facilitating overcurrent device operation during ground-fault events, which is a performance function. Care must be taken to ensure good electrical connections are made for all of the conductors including, but not limited to, the service grounding scheme. In addition, Section 110.12 requires electrical conductors and equipment to be installed in a workmanlike manner. Any worthy training program must include strong emphasis on craftsmanship and training people in a way that results in a skilled and confident workforce.

Part I of Article 250 provides general requirements for grounding and bonding. In the 1999 NEC, Article 250 was revised in a unique fashion to include text on what grounding and bonding must accomplish in electrical wiring. Prior to that edition, there were only fine-print notes (now informational notes) that explained grounding and bonding performance. Section 250.4 was a huge step in improving the understanding of the NEC requirements related to this subject. These general provisions tell users how grounding and bonding perform in grounded systems and ungrounded systems. In other words, these provisions explain what is anticipated when grounding and bonding meet the other prescriptive requirements in the NEC.

Analyze the performance language closely to develop a strong understanding of what must happen electrically. This will simplify an electrician’s understanding of the other prescriptive requirements in Article 250 and throughout the NEC. In its simplest form, grounding is made up of two concepts: system grounding and equipment grounding.

Systems are either grounded or ungrounded. Grounded systems include one conductor intentionally connected to the ground. Other than at the system’s point of grounding, grounded system conductors and equipment grounding conductors are generally kept separate from each other. A clear differentiation between these two conductors must be made.

In the simplest form, bonding is made up of two concepts: connecting together for continuity and connecting together for conductivity. Bonding must fulfill both functions. When done correctly, bonding results in effective paths for ground-fault current and minimizes potential differences between conductive parts and equipment that is required to be bonded.

Workers must realize the performance aspects of grounding and bonding together as electrical systems are constructed in the field. With a thorough understanding of what grounding and bonding are intended to accomplish for electrical systems and equipment, the NEC prescriptive requirements are much more understandable and easily applied in electrical system design and installation. Refer to NEC Section 250.4 and the definitions of grounding and bonding in Article 100.

About the Author

Michael Johnston

Executive Director of Standards and Safety, NECA
Michael Johnston is NECA’s executive director of standards and safety. He is chair of the NEC Technical Correlating Committee. He served as a principal representative on NEC CMP-5 representing IAEI for the 2002, 2005, and 2008 cycles and is currently...

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