An equipment grounding conductor (EGC) installed with a branch circuit or feeder circuit performs three important functions in the electrical safety system. EGCs provide a path that connects equipment to ground, thereby performing grounding functions. The EGC extends the ground connection to various points in the electrical system because it is generally installed with feeders or branch circuits.
The role of grounding is to place a conductive object (equipment) at or as close to earth (ground) potential as possible. The EGC limits voltages above ground potential on conductors and equipment enclosures during normal operation and conditions such as ground faults or short circuits.
Bonding is another important function EGCs perform. The definition uses the words “connect” and “together.” The act of connecting conductive parts together is a bonding function. For example, when an EGC is installed from one metallic outlet box to another and is connected to the metal box at both ends, the boxes become grounded and are bonded electrically together.
The third important role the EGC has is to serve as an effective current path during abnormal events such as ground faults.
The conductor must carry the maximum available fault current for the time it takes the overcurrent protective device to open and clear the event from the circuit. Section 250.4(A)(5) provides the performance requirements and criteria for an effective ground-fault current path. Ideally there will not be a ground fault on the circuit, but insulation breakdown or failure can occur, resulting in the undesirable ground fault. Insulation can be in the form of a dielectric material or air space, such as the space between busbars in a switchboard or panelboard. Ground faults are typically unintentional. In addition to wire insulation failure, a ground fault can result from human error or accidents such as the dropping of a conductive tool in an electrical enclosure during work on energized equipment. During those events, the EGC must withstand the higher level of current to perform its all-important safety function. EGCs provide grounding for equipment, perform bonding functions and facilitate overcurrent device operation, making them an important component of the electrical-safety system.
Section 250.118 provides the conductive materials and wiring methods that can be used as EGCs with feeders and branch circuits. List item 1 in Section 250.118 states EGCs can be made of copper, aluminum or copper-clad aluminum material. These conductor materials can be in the form of a wire (stranded or solid) or busbar of any shape, and they can be insulated, covered or bare.
Section 110.12 requires electrical conductors and equipment to be installed in a neat and workmanlike manner. This also applies to EGCs installed with feeders and branch circuits. Where the wiring method—such as rigid metal conduit or electrical metallic tubing—is installed and serves as the required EGC, the installation must conform to the provisions in Section 110.12. This includes, but is not limited to, sufficient support and methods of securing the wiring method. If the conduit or tubing is secured properly, it should not be subject to movement that could compromise its performance as an effective ground-fault current path due to loosening of fittings.
All connections and joints must be tightened using suitable tools. This is another basic workmanship requirement in Section 110.12. It is important to tighten fittings because of the functions they are expected to perform both in normal operation and during abnormal conditions such as ground faults. Loose electrical fittings, such as set-screw couplings, connectors and locknuts, introduce impedance into the ground-fault current path and could affect quick operation of overcurrent devices.
Chapter 3 also includes requirements for effectively securing and supporting conduit and other raceways that must perform as an effective ground-fault current path. The integrity of the effective ground-fault current path established by the wiring method itself depends on effective, NEC-compliant support and securing of the raceway system. (NECA publishes several standards that address good workmanship in electrical construction. For more information, visit www.neca-neis.org.)
Section 250.120 provides installation requirements for EGCs of all types. Essentially, whatever EGC is installed, the applicable provisions must be met. If a cable tray is the EGC, it must meet the applicable requirements in Articles 250, 300 and 392 relative to cable trays performing as EGCs. If a raceway such as electrical metallic tubing (EMT) is installed, it is required to meet the applicable installation requirements in Articles 250, 300 and 358. The fittings and terminations used with the chosen wiring method must be suitable for use with the type of installed wiring method. For example, Section 358.6 requires fittings (connectors, couplings and locknuts, for example) used with EMT to be listed for use with EMT.
About The Author
JOHNSTON is NECA’s executive director of codes and standards. He is a member of the NEC Correlating Committee, NFPA Standards Council, IBEW, UL Electrical Council and NFPA’s Electrical Section. Reach him at [email protected].