Original General Order
Detailed Construction Requirements for Supply Lines
(Class H, L
and T Circuits)
A. Material and Size
(1) Grounding Conductors: The grounding conductor from each ground electrode to the base of pole shall be not less than 1 foot below the surface of the ground and shall have not less conductivity and mechanical strength than No. 1 AWG medium-hard-drawn stranded copper. From the No. 1 AWG or larger conductor to the common neutral line conductor, the grounding conductor shall be continuous without splices and shall be not less than No. 4 AWG copper.
(2) Grounding Electrodes: Ground electrodes on common neutral systems shall conform to the following specifications as a minimum:
Not part of a water
system: Ground electrodes which are not part of a water system shall be
one-piece corrosion-resisting metal rods or pipes (or equivalent in physical
and electrical qualities) 5/8 inch in diameter by 8 feet in length and driven
to a minimum depth of 8 feet below the surface of the ground.
The driven ground rod, pipe, or equivalent shall be located not less than 2 feet from the surface of the pole. Where two or more such rods are installed, they shall be located at not less than 6-foot centers and separation required from the surface of the pole shall not be held to apply to the connection between rods.
b) Part of a water system: Where ground conductors are attached directly to a water pipe system, they shall be connected on the main line side of any water metering equipment.
B. Neutral Conductors
(1) Location: The common neutral grid system shall be grounded at intervals not greater than 1500 feet. On branch circuits extending from a grid, where return loop paths are not available, the common neutral line conductor shall be grounded at intervals not greater than 800 feet. Each transformer installation on a branch circuit without a loop return shall be so located that there will be one or more metallic water pipe system grounds, each of a resistance not greater than 3 ½ ohms, on each side of the transformer installation.
(2) Resistance: Where a common neutral system is used the resistance of the continuous metallic neutral grid to ground at any point shall not exceed 3 ½ ohms at any time.
If, after definite effort has been made, it is found not practicable to meet the above requirement, the following alternate requirement will be accepted:
The resistance between any point of said grid and the ground connection at the substation shall not exceed 1 ohm, and furthermore, the resistance of the ground connection at the substation either shall not exceed 1 ohm or, if in excess of 1 ohm, shall be lower that that of any individual ground connection on the grid and in no case in excess of 2 ohms.
Measurement of resistance by any approved method is recognized. In lieu of measurements of resistance of the neutral conductor under the second alternative prescribed above, approved joints and demonstrable calculations will be accepted.
Ground conductors of Transformers on common neutral systems shall conform to the requirements of Rule 59.4-A1.
On common neutral systems, each transformer installation on a branch circuit without a loop return shall be so located that there will be one or more metallic water pipe systems grounds of a resistance not greater than 3 ½ ohms on each side of the transformers installation.
A transformer installation located on a grid section of a common neutral system requires no independent ground provided that there is a ground connection, having a resistance not in excess of 3 ½ ohms, to the common neutral line conductor either at the transformer pole or at an adjacent pole.