GO 64-A, Supplement 1

Supplement Number 1

Neutral conductors of supply circuits shall be considered as carrying the same voltage as the current carrying wires.

The grounding of the neutral in single phase or polyphase systems is permitted only for the purpose of stabilizing the neutral of the system, and not for use as a return conductor.

Independent grounds or independent ground connections, the resistance of which does not exceed 25 ohms shall be provided for the following:

The neutral wire of 4 wire, 3 phase systems where the line voltage exceeds 2500.

Neutral conductors of supply circuits other than distribution systems of five thousand (5000) volts or less with common primary and secondary grounded neutrals, shall be considered as carrying the same voltage as the current-carrying wires. Where a common primary and secondary grounded neutral distribution system is installed the neutral conductor may be considered as carrying the same voltage as any of its related system conductors, compliance with the special practices and construction requirements being necessary.

On a common primary and secondary grounded neutral distribution system, the following pro- visions shall apply:

Wherever existing plant permits, cross ties of the neutral conductor shall be made to form a continuous interconnected grid network. From each grid section there shall be two (2) or more separate and continuous metallic return conductors to the source of supply.

If two (2) return conductors only are used, each shall have a minimum area of approximately fifty (50) per cent of the area of the phase conductor of the largest overhead feeder serving the area. (See Table No. 6-A of Rule 49.4-B for minimum sizes.)

If more than two (2) return conductors are used, the current-carrying capacity of the return system shall be such that a break in any one (1) path shall leave two (2) or more return paths which, combined shall have a minimum area of approximately fifty (50) per cent of the area of the phase conductor of the largest overhead feeder serving the area, thus providing adequate current-carrying capacity for full load current. (See Table No. 6-A of Rule 49.4-B for minimum sizes.)

The common neutral grid system shall be grounded at intervals not greater than fifteen hundred (1500) feet. On branch circuits extending from a grid, where return loop paths are not avail- able, the common neutral line conductor shall be grounded at intervals not greater than eight hundred (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 three and one-half (3.5) ohms, on each side of the transformer installation.

The grounding of the neutral in single phase or polyphase systems is permitted only for the purpose of stabilizing the neutral of the system, and not for use as a return conductor.

Independent grounds or independent ground connections, the resistance of which does not exceed twenty- five (25) ohms, shall be provided for the following:

Low voltage power or lighting circuits other than common primary and secondary grounded neutral circuits.

The neutral wire of 4-wire, 3-phase systems where the line voltage exceeds 2500, other than common primary and secondary grounded neutral systems.

Where a common primary and secondary grounded neutral distribution system is used the resistance of the continuous metallic neutral grid to ground shall conform to the following requirement:

(1) The resistance between said grid and ground at any point shall not exceed three and one-half (3.5) ohms at any time.

If, after definite, effort has been made, it is found not practicable to meet the above requirements, the following alternate requirement will be accepted:

(2) The resistance between any point of said grid and the ground connection at the substation shall not exceed one (1.0) ohm, and, furthermore. the resistance of said ground connection at the sub- station either (a) shall not exceed one (1.0) ohm, or (b), if in excess of one (1.0) ohm, shall be lower than that of any individual ground connection on the grid, and in no case in excess of two (2.0) ohms.

Measurement of resistance by any approved method is recognized. In lieu of measurements of resistance of the neutral conductor under (2) above, approved joints and demonstrable calculations will be accepted.

In common primary and secondary grounded neutral systems, ground electrodes shall conform to the following minimum specifications:

(a) One-piece corrosion-resisting metal rod or pipe (or equivalent in physical and electrical qualities) five-eighths (5/8) inch diameter by eight (8) feet in length and driven to a mini- mum depth of eight (8) feet below the surface of the ground.

(b) Water pipe systems: Where ground wires are attached directly to a water pipe system, they shall be connected on the main line side of any water metering equipment.

The driven ground rod, pipe or equivalent shall be located not less than two (2) feet from the surface of the pole. Where two or more are installed, they shall be located at not less than six (6) foot centers. The separation required from the surface of the pole shall not apply to a connection to the water pipe system or to the connection between two or more driven rods or pipes.