Section 9/Grounding Methods for Electric Supply and Communications Facilities
NESC Section 9 (Rules 091 through 099) covers grounding electrodes, grounding conductors, and connection methods for supply stations, overhead lines, and underground systems.
NESC Section 9 establishes grounding requirements for electric supply and communications facilities. Rule 092 specifies where grounding connections must be made, including at each supply station, at intervals along distribution lines, and at equipment housings. Rule 093 covers grounding electrodes: driven ground rods must be at least 8 feet long and driven to their full length, and where a single rod does not achieve 25 ohms resistance, a supplemental electrode must be installed. Rule 094 specifies grounding conductor materials and sizes. Rule 095 addresses grounding conductor current-carrying capacity, which must be adequate for the maximum fault current and fault duration. Rule 096 covers continuity requirements for grounding systems, ensuring connections are permanent and not easily interrupted by physical damage or corrosion.
Why this section exists
Grounding on the utility side of the meter serves different purposes than premises wiring grounding under the NEC. Supply station grounding must handle fault currents that are orders of magnitude larger than building-side faults, limit ground potential rise (GPR) to protect people near the station during faults, and stabilize system voltages across the distribution network. The IEEE 80 grounding grid design procedure is used to implement these NESC requirements at substations, with step and touch voltage limits governing the grid geometry. The 25-ohm electrode resistance threshold ensures adequate fault current return and reliable protective relay operation.
What plan reviewers look for
Plan reviewers check substation grounding plans for electrode locations, conductor sizes, and connection details. They verify that the grounding grid conductor size is adequate for the available fault current and clearing time. They check that all equipment housings, fences, structural steel, and above-grade metallic structures within the station are bonded to the grounding grid. For distribution line grounding, they verify multi-grounded neutral connections at the required intervals. For overhead line designs, they check that pole ground connections are shown where required and that conductor clearances per Rule 23 account for the grounding configuration.