go 95 rule 59.4

Detailed Construction Requirements for Supply Lines
(Class H, L and T Circuits)

(1) Grounding Conductors: The grounding conductors of the common neutral system shall conform to each of the following requirements:

a) The grounding conductor from each ground rod to the base of the pole shall not be less than 1 foot below the surface of the ground.

b) The grounding conductor from each ground rod to the base of the pole shall not have less ampacity and mechanical strength than the grounding conductor from the base of the pole to the common neutral conductor.

c) The grounding conductor from the ground rod to the common neutral conductor shall be continuous, unless suitable electrical compression connections are used.

d) The grounding conductor shall have a minimum ampacity equivalent to No. 4 AWG copper.

(2) Ground Rods (Ground Electrodes): Ground rods on common neutral systems shall conform to each of the following requirements:

a) Ground rods shall be one–piece corrosion–resisting metal rods or pipes (or equivalent in physical and electrical properties).

c) Ground rods shall be driven into the ground so that one end of the ground rod is at a minimum depth of 8 feet below the surface of the ground.

d) Pole–butt plates or wrappings shall not be used either in lieu of the aforesaid ground rods, pipes, or as electrodes supplementary thereto.

e) On branch circuits extending from the grid, where return metallic paths are not available, the driven ground rod(s), pipe(s), or equivalent shall be located 24 inches or more from the surface of the pole. This 24 inches clearance does not apply to the grounding conductor between ground rods.

f) Where two or more such rods are installed, they shall be located at not less than 6 foot centers.

(1) Locations: The common neutral grid system shall be grounded at intervals not greater than 1,000 feet. On branch circuits extending from a grid, where return loop paths are not available, the common neutral conductor shall be grounded at intervals not greater than 500 feet. For each transformer installed on a branch circuit without a loop return, the transformer shall be so located that there will be one or more grounds, of a combined resistance not greater than 3.5 ohms.

(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 3.5 ohms at any time.

EXCEPTION: If, after a 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 the continuous metallic neutral grid and the ground connection at the substation shall normally not exceed 1 ohm. However, if the resistance exceeds 1 ohm, it shall be lower than that of any individual ground connection on the grid, but in no case shall it be greater than 2 ohms.

(3) Measurement of Resistance: Measurement of resistance by any suitable method is recognized.

Note: Under the requirements of Rule 59.4–B2, when the resistance exceeds 1 ohm but is to be less than 2 ohms, suitable ground rod connections (joints) and demonstrable calculations, instead of neutral conductor resistance measurements, 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 with transformers installed on a branch circuit without a common neutral loop return, each transformer shall be so located that there will be one or more grounds of a combined resistance not greater than 3.5 ohms.

A transformer installation located on a grid section of a common neutral system requires no independent ground provided there is a ground connection, having a resistance not in excess of 3.5 ohms, to the common neutral conductor either at the transformer pole or at an adjacent pole.