General Order 95
Detailed Construction Requirements for Supply Lines
(Class H, L and T Circuits)
Conductors of common neutral systems shall be of suitable corrosion–resisting materials, but shall not be of galvanized iron or steel.
Note: Revised January 21, 1992, by Resolution
SU–10; November 6, 1992 by Resolution SU–15.
In common neutral systems, the neutral line conductor shall have a minimum ampacity at each location of not less than one–quarter (25%) that of the largest related primary phase line conductor, provided that the short time ampacity of the neutral conductor is maintained. The short time ampacity of a common neutral conductor is either: the current that a non–insulated conductor can carry for the time which the current flows without annealing, melting or separating under the applied tensions; or the current that an insulated conductor can carry for the time that the current flows without damaging the insulation.
No neutral line conductor need have greater ampacity than either: the phase line conductor which would supply the ground current, or the maximum current which can flow through the neutral line conductor to the ground or electrode of the common neutral grid system. The neutral line conductor shall have a short time ampacity adequate for the fault current which can flow in the neutral line conductor for the operating time of the system protective device. If this value cannot be readily determined, the continuous ampacity of the neutral line conductor shall not be less than the full load continuous current of the system supply transformers or other source of supply. In no case shall the neutral conductor have less ampacity than No. 6 AWG medium–hard–drawn copper wire.
Note: Revised March 29, 1966 by
Decision No. 70489; August 9, 1966 by Decision No. 71094; November 6, 1992
by Resolution SU–15.
All electrical connections shall be of suitable electrical and mechanical design.
D. Arrangement and
The arrangement and continuity of common neutral conductors shall conform to the following requirements:
(1) Continuity: Cross ties of the common neutral conductor shall be
made to form a continuous interconnected grid network.
(2) Minimum Number of Return Paths: There shall not be less than two
separate and continuous metallic return conductor paths from the grid network
to the substation constituting the source of supply thereto.
(3) Two Return Conductor Paths: If only two return common neutral conductors
paths are used, each path shall have a minimum ampacity of not less than one–quarter
(25%) that of the largest related primary phase conductor, provided that
the short time ampacity of the common neutral conductor is maintained.
(4) More Than Two Return Conductor Paths: If more than two return
common neutral conductors paths are used, the ampacity of the return system
shall be such that a break in any one path shall leave two or more return
common neutral paths. These combined paths shall have a minimum ampacity
of not less than one–quarter (25%) that of the largest primary phase conductor
of the overhead feeder serving the area, provided that the short time ampacity
of the common neutral conductor is maintained.
(5) Primary and Secondary Neutral Conductors: Primary neutral
conductors or secondary neutral conductors, where continuous, may be used
as a return loop from a common neutral provided they have sufficient ampacity
as specified in Rule 59.3–B
and are grounded throughout in accordance with the requirements for common
neutral conductors as specified in Rule
. Primary or secondary neutral line conductors so used shall be carried
in the normal primary or secondary positions, respectively.
Note: Revised March 29,1966 by Decision No. 70489; August 19, 1966 by Decision
No. 71094; November 6, 1992 by Resolution SU–15.
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 shall be located in a related secondary 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 Metal Riser Conduits: Common neutral conductors may be
installed in the same metal riser conduits with related phase conductors,
provided that the metal riser conduit is effectively grounded.
Note: Revised November 6, 1992 by Resolution SU–15.
(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 at each pin position with the letters “CN”. A weather and corrosion–resisting material shall be used and the letters shall be clearly legible.
Optional marking methods are:
(1) A 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 a distance not more than 12 inches from
the surface of the conductor support.
(2) Solid letters not less than 3 inches in height or a sign showing the
letters “CN” not less than 3 inches in height, solid or with letters cut
out therefrom. Said letters or signs shall be placed on the face of a crossarm,
suitable for attaching the letters or signs, directly beneath the common
neutral support, or said letters or signs shall be placed on the surface
of the pole beneath the common neutral support.
Note: Revised January 21, 1992, by Resolution SU–10.