Original General Order 95

Section V

Detailed Construction Requirements for Supply Lines

(Class H, L and T Circuits)

59.3    Conductors

A.    Material

Conductors of common neutral systems shall be of copper, copper-covered steel, bronze, stranded composites of any of the foregoing, aluminum, aluminum cable steel reinforced, or of other corrosion-resisting metal, but shall not be galvanized iron or steel.

Related phase and neutral line conductors shall be of the same material, except that the neutral conductor may be of copper.

B.    Size

In common neutral systems the common neutral line conductor shall have a cross-sectional area approximately 50 percent or more of the area of the largest related primary phase conductor, as set forth in Table No. 14 and in no case shall have less conductivity or mechanical strength than No. 6 AWG medium-hard-drawn copper wire.

This Table is based on the requirement that the common neutral line conductor shall have a minimum area of approximately 50 per cent of the area of the largest related primary phase conductor and that the phase and neutral conductors are of the same material.  Where these are not of the same material, the copper conductance equivalents of the table will be considered as meeting the requirements.

C.    Connections

All electrical connections shall be of suitable electrical and mechanical design.

D.    Neutral Conductors

The arrangement and continuity of common neutral conductors shall conform to the following requirements:

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 or more separate and continuous metallic return conductors to the source of supply.

If two return conductors only are used, each shall have a minimum area of approximately 50 per cent of the area of the primary phase conductor of the largest overhead feeder serving the area.  (See Table No. 14 of Rule 59.3-B for minimum sizes.)

If more than two return conductors are used, the current-carrying capacity of the return system shall be such that a break in any one path shall leave two or more return paths which, combined, shall have a minimum area of approximately 50 per cent of the area of the primary phase conductor of the largest overhead feeder serving the area, thus providing adequate current-carrying capacity for full load current.  (see Table No. 14 of Rule 59.3-B for minimum sizes.)

Primary neutral conductors or secondary neutral conductors, where continuous, may be used as a return loop from a common neutral provided they are of sufficient current-carrying capacity as specified in Rule 59.3-B and provided that they are grounded throughout in accordance with the requirements for common neutral line conductors as specified in Rule 59.4-B. Primary or secondary neutral line conductors so used shall be carried in their normal primary or secondary positions respectively.

E.    Common Neutral Line Conductor Location

(1)    With Primary Circuits: On poles where all circuits are in excess of 750 volts, the common neutral line conductor may be located in a conductor position in the primary space.

(2)    With Secondary Circuits: On poles where all circuits of a common neutral system are of less than 750 volts, the common neutral line conductor shall be located in a secondary conductor position.

(3)    With Primary and Secondary Circuits: On poles where circuits of a common neutral system are of more and less than 750 volts, the common neutral line conductor position; or common neutral line conductors may be located in both primary and secondary positions provided a metallic connection of a size not smaller than the largest neutral line conductor involved is installed between the neutral conductors in accordance with the construction requirements for ground wires on poles at each location where a ground is required, and provided proper designation (see Rule 59.3-F) is made of the common neutral conductor in the primary position.

(4)    In Conduits: Common neutral conductors may be installed in the same conduits with related phase conductors, provided that the insulation of the neutral conductor is not less than that required of the phase wires and, further, that it is treated as a phase wire for the entire run between terminals.  Where the conduit installation is an effectively grounded metal riser pipe, the reference to insulation of the common neutral need not apply, provided the neutral conductor is connected to both ends of the riser pipe and effectively, grounded.

(5)    Under Crossarms: Incidental pole wiring connected to the common neutral conductor may be stapled to the underside of crossarms, provided the installation is such as to offer the least possibility of contact to workmen and such wiring under crossarms in the primary position is covered by a suitable protective covering.

F.    Designation of Common Neutral

In common neutral systems, where the common neutral line conductor is installed in a primary pin position, it shall be designated by an approved noncorrosive metal tag having a minimum diameter of not less than 1 inch upon which shall be permanently imprinted the letters “CN” not less than 5/16 inch in height.  Said tag shall be attached securely to and maintained on the common neutral conductor at each pin position of line arm and buck arm at a distance not more than 12 inches from the face of the crossarm on the climbing side of each pole and so installed as to be clearly visible at all times.