Original General Order 128

Section III

Requirements For Supply Systems

36.5    Grounding and Bonding of Conductors and Equipment

A.    General

Supply conductors and equipment of the following types shall be bonded in manholes and at other locations where conductors and equipment are accessible and in proximity to one another, and shall be grounded in accordance with Rule 36.5-C:

(1)    Transformer Windings: Transformer windings not exceeding 250 volts (except those used exclusively for energizing street lighting circuits and those used exclusively for energizing signal and track circuits) shall be effectively grounded at the points specified in the following:

a)    Single Phase Systems:

2-wire 120 volt: one conductor.

2-wire 240 volt: intermediate point or, if not available, one conductor.

3-wire 120/240 volt: mid point.

b)    Two Phase Systems:

3-wire 240 volt: point common to both windings.

4-wire 120/240 volt: mid point on one phase.

4-wire 240 volt  mid points of both windings connected together.

5-wire 120/240 volt mid points of both windings connected together.

c)    Three Phase Systems:

3-wire Delta 120 or 240 volt: mid point of one winding or, if not available, a point common to two windings.
3-wire and 4-wire Star 120, 208, 240, or 120/208 volt, and 3-wire T or Scott 240 volt: point common to all windings or, if not available, one conductor.

(2)    Supply Circuits 0-750 Volts: Neutral conductors of 0-750 volt supply circuits.

(3)    Supply Circuits More than 750 Volts: Neutral conductors of supply circuits of more than 750 volts.

(4)    Metal Sheaths, Shields and Pipes: Metal sheaths and shields of supply cables and metal pipes and conduits enclosing supply cables, except as provided by Rule 36.5-B.

(5)    Metal Cases Supply Equipment: Metal cases of transformers, switches, and other supply equipment.

(6)    Above-Ground Metal Enclosures: Above-ground metal enclosures in which supply conductors are terminated.

(7)    Lightning Arresters.

B.    Exception

Metal sheaths and shields of cables and pipes of pipe-type cables may be sectionalized, and/or not bonded to other grounded equipment and conductors in commonly accessible locations as required by Rule 36.5-A, in order to mitigate corrosion or to limit induced circulating currents; provided that each run of such sheath, shield, or pipe is effectively grounded and the induced voltage thereon does not exceed 25 volts to ground under normal operating conditions.

C.    Grounding Methods

Conductors and equipment required by Rule 36.5-A to be grounded shall be effectively grounded by one or more of the following methods:

(1)    Burial in Earth: Bare neutral conductors, metallic cable sheaths and shields, metal pipes and metal conduits may be grounded by burying them directly in the earth.

(2)    Grounding Electrodes: Conductors and equipment may be grounded by connections at one or more locations to driven ground rods or other suitable grounding electrodes.

(3)    Bonding: Conductors and equipment may be grounded by bonding at one or more locations to conductors or equipment grounded in accordance with Rule 36.5-C(1) or Rule 36.5-C(2).

D.    Grounding And Bonding Conductors

(1)    Material: Conductors used for bonding and grounding connections shall be of copper or other corrosion resistant material, or shall be suitably protected against corrosion.

(2)    Conductivity: Conductors used for bonding and grounding connections shall have sufficient conductivity to carry the fault currents that may be imposed upon them by the associated system, and in no case less than the conductivity equivalent of No.6 AWG Copper.

(3)    Method of Attachment: Grounding and bonding conductors shall be attached by means of suitable lugs, pressure connectors, clamps, welds, or other suitable means. Clamps shall not be used for direct attachment to lead sheaths of cables.