|
A. All metallic sheaths, armors, and conduits enclosing power conductors shall be electrically continuous throughout and shall be grounded effectively. B. Metallic frames, casing, and other enclosures of stationary electric equipment that can become "alive" through failure of insulation or by contact with energized parts shall be grounded effectively, or equivalent protection shall be provided. C. Three-phase alternating current circuits used underground shall contain either a direct or derived neutral which shall be grounded through a suitable resistor at the power center, and a grounding circuit, originating at the grounded side of the grounding resistor, shall extend with the power conductors and serve as the grounding conductor for the frames of all the electrical equipment supplied power from that circuit. Grounding resistors that are manufactured to meet the extended time rating as set forth in IEEE Standard 32-1972, formerly AIEE Standard 32, are deemed to meet the requirements of this section. High-voltage circuits extending underground shall be supplied with a grounding resistor of a proper Ohmic value located on the surface to limit the voltage drop in the grounding circuit external to the resistor to not more than 100 volts under fault conditions. The grounding resistor shall be rated for maximum fault current continuously and insulated from ground for a voltage equal to the phase-to-phase voltage of the system. All resistance-grounded alternating circuits used underground shall include a fail-safe ground check circuit to monitor continuously the grounding circuit to assure the continuity of the ground conductor. 1966, c. 594, § 45.1-79; 1994, c. 28 ; 1999, c. 28 ; 2011, cc. 28 , 28 .
|
