Historically, grounding and bonding have been regarded as the primary methods of protecting systems, property and personnel from electric shock hazards and fire, while offering significant advantages in system operation. Many have debated whether greater protection is achieved by grounding systems and equipment or by isolating or otherwise not grounding them.

Grounding system

Contrary to the belief of many, grounding performs only some of the protective functions necessary for equipment and systems designed and installed according to the National Electrical Code. While grounding provides the protection described above, the NEC strongly emphasizes the critical role of an effective ground-fault current path in electrical safety systems and how it relates to effective operation of overcurrent protective devices. This path for ground-fault current is essential in grounded systems.

During a ground-fault event, current will return to the source through multiple paths, such as through equipment grounding conductors, the earth, conductive equipment parts, a human body or any combination of ground-fault return paths.

Grounding and bonding circuits are safety circuits for electrical services, feeders and branch circuits in today’s wiring systems. Section 250.4 provides performance language to assist users by describing what grounding and bonding must accomplish for the systems. Performance-based rules in the Code help make many other prescriptive requirements easier to apply and follow.

Grounding stabilizes voltages during normal operation. Electrical equipment is grounded to establish the same or close to the same potential between the equipment and ground (earth).

Electrical systems are grounded to limit potentials (voltages) imposed by lightning, line surges or unintentional contact with higher-voltage lines. Grounding also stabilizes voltages during normal operation. Electrical equipment is grounded to establish the same or close to the same potential between the equipment and ground (earth).

When electrically conductive parts are effectively bonded together, electrical continuity and conductivity are established. An important part of the grounding and bonding scheme is constructing an effective ground-fault current path. Take care to ensure that effective electrical connections are made for all the conductors, including, but not limited to, the service grounding scheme. Section 110.12, “Mechanical Execution of Work,” requires electrical conductors and equipment to be installed in a professional and skillful manner. Any worthy training program must emphasize good workmanship. Good electrical installations generally look good and perform well.

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 (performance language) in electrical wiring. Prior to that, there were only fine-print notes (now informational notes) that explained grounding and bonding performance.

Section 250.4 brought a significant improvement by helping users understand requirements related to this subject. These general provisions explain how grounding and bonding perform in grounded and ungrounded systems, and what is anticipated when grounding and bonding meet the NEC minimum requirements. The performance language must be analyzed closely to develop a strong understanding of what must happen electrically. This helps simplify understanding and improve accurate application of the other prescriptive requirements in Article 250 and throughout the NEC.

In its simplest form, grounding is made up of two concepts: system and equipment grounding. Electrical systems are either grounded or ungrounded. Grounded systems include one conductor of the system (source) that is intentionally connected to the ground. Grounded system conductors and equipment grounding conductors or ground are generally not permitted to be connected other than at the point of grounding for the service or system. A clear differentiation and separation between these two conductors must be made.

Bonding functions

In the simplest form, bonding has two functions: connecting for continuity and conductivity. Bonding must fulfill both functions in grounded and ungrounded systems. Bonding performed correctly results in effective paths for ground-fault current and minimizes potential differences between conductive parts and equipment required to be bonded. 

With a thorough understanding of what grounding and bonding are intended to accomplish, the NEC prescriptive requirements are much more understandable and easier to apply in design and installation.

Whether a system is grounded or not, specific performance requirements apply. Sections 250.4(A) and (B) provide a detailed breakdown of the grounding and bonding performance requirements for grounded and ungrounded electrical systems. If the Code or a specification requires an ungrounded system, other rules such as ground-fault detection systems are triggered.