Current through Register Vol. 54, No. 50, December 14, 2024
Section 39.65 - Ground conductor(a)Material and continuity. The ground conductor shall be of copper or of other metal which will not corrode excessively under the existing conditions and, if practicable, shall be continuous. Joints shall be made and maintained so as to conform to the resistance and current-carrying capacity requirements of § 39.69 (relating to ground resistance). Ground connections from circuits should not be made to jointed piping within buildings, except that water piping outside of meters and beyond any point which is liable to disconnection, may be used. Reference should also be made to § 39.68 (relating to methods of ground connection). No automatic cutout shall be inserted in the ground conductor or connection except in a ground connection from equipment where its operation will immediately result in the automatic disconnection from all sources or energy of the equipment so grounded; no switch shall be so inserted except in plain sight, provided with distinctive marking and effectively isolated from unqualified persons. Reference should also be made to § 39.67 (relating to attachment of ground conductor).(b)Size and number. The size and number of ground conductors shall be as follows: (1) For grounding circuits the ground conductors shall have a combined cross section and current capacity sufficient to insure the continuity of the ground connection and its continued compliance with § 39.69, under conditions of excess current caused by accidental grounding of any normally ungrounded conductor of the circuit. No individual ground conductor for electrical circuits shall have less current capacity than that of a No. 6 copper wire, except that for additional grounds after the first on any circuit, smaller ground wires may be used, provided that they are in no case smaller than the conductor to which they are attached nor smaller than No. 10 copper.(2) For lightning arrester ground connections the ground conductor or conductors shall have a current carrying capacity sufficient to insure continuity of the ground connection under conditions of excess current caused by or following discharge of the arrester. No individual ground conductor shall be smaller than a No. 6 wire.(3) Electrical equipment shall conform to the following:(i) For electrical equipment the current-carrying capacity of a ground conductor shall be not less than that provided by a copper wire of the size indicated in the following table: | Capacity of Nearest Automatic Cutouts (in amperes) | Required Size of Ground Conductor A.W.G. |
| 200-500 | 4 |
| 100-200 | 6 |
| 30-100 | 10 |
| 10-30 | 14 |
(ii) If there is no cutout protecting the equipment, the size of ground conductor shall be determined by the design and operating conditions of the circuit.(iii) In the portable cord to portable equipment protected by fuses not greater than 10-ampere capacity, a No. 18 ground wire may be used.(c)Mechanical protection and guarding against contact. Mechanical protection and guarding against contact shall be provided as follows:(1) If exposed to possible mechanical injury the ground conductor shall be protected by substantial conduit or other guard.(2) Guards for the ground conductors of the lightning arresters should be of nonmagnetic material unless the ground conductor is electrically connected to both ends of the guard.(3) If resistance of the ground connection is in excess of the values in § 39.69, for water pipe grounds, the ground conductor, except in rural districts, shall be protected and guarded by being enclosed in insulating conduit or molding to protect persons from injury by coming into contact with it. A high resistance may exist where artificial grounds are necessarily permitted in lieu of the preferable grounds to buried metallic water piping systems.(4) Mechanical protection and insulating guards should extend for a distance of not less than 8 feet above any ground, platform, or floor from which ground conductors are accessible to the public, however, the following precautions are recommended:(i) Insulating mechanical protection is advisable for single arrester grounds, even when the connection is made to a water piping system, and has therefore a low resistance, since a single connection is liable to be accidentally broken.(ii) Even where ground connections have a resistance not exceeding that specified in § 39.69, and no guard is therefore provided, or, as an additional protection to persons even where guards are used artificial grounds may be arranged to minimize the potential gradient along the surface of the earth by use of radial connecting wires underneath the earth surface or by other suitable means.(5) A circuit ground conductor shall be guarded as required for current-carrying conductors of the circuit, unless the ground conductor is entirely outside buildings, has strength and current capacity not less than that of No. 6 copper wire, and the circuit is elsewhere grounded by other ground conductors, except that in stations substantial bare ground busses may be used.(d)Underground conductors. Wires used for ground conductors, if laid underground shall, unless otherwise mechanically protected, be laid slack to prevent their being readily broken, and shall have joints carefully painted or othewise protected against corrosion. This section cited in 34 Pa. Code § 39.61 (relating to applicability); 34 Pa. Code § 39.62 (relating to scope); 34 Pa. Code § 39.63 (relating to modification or waiver of provisions); 34 Pa. Code § 39.66 (relating to nature of ground connection); 34 Pa. Code § 39.68 (relating to methods of ground connection); 34 Pa Code § 39.103 (relating to protective grounding); 34 Pa. Code § 39.183 (relating to ground wires); 34 Pa. Code § 39.197 (relating to grounding); 34 Pa. Code § 39.219 (relating to grounding or isolating service conduits); 34 Pa. Code § 39.292 (relating to grounding noncurrent-carrying parts); and 34 Pa. Code § 39.304 (relating to grounding of arresters for signaling systems).