Previous Code

Next Code


General Order 64-A


Section V


Detailed Construction Requirements For Supply Lines

(Class H, L and T Circuits)


58.4    Transformers.


A.    Location.

Transformers shall be so located that the case, hanger and other normally Unenergized metal parts clear the 0-750 volt conductor level by not less than 10 inches vertically and clear the 750-7500 volt conductor level of other circuits by not less than 12 inches vertically.

Excepted from the above is the clearance of the top of the case or hanger of the transformer installed on combination cross arms, in which case a clearance of not less than 3 inches from the 0-750 volt conductor level shall be maintained.
  Transformer heel arms shall not be utilized as conductor supports except:


Where necessary to clear the transformer leads from the transformer case or other conductors.


Where conductors so supported are of 0-750 volts and clear the transformer case not less than 18 inches horizontally and are at least 18 inches vertically below the plane of the “drip loop” of the transformer primary lead wire, a single service drop may be installed.


Where more than one transformer is installed on a pole, all transformers shall be hung on the same side of the pole, in order to give free access to all equipment on the pole.


B.    Grounding of Windings.

Transformer windings not exceeding 250 volts to ground (except those used exclusively for energizing signal and track circuits) shall be grounded as follows:


Single Phase Systems:  In 2 wire (nominal 110 volt) systems one wire shall be grounded; 2 wire (nominal 220 volts) systems or 3 wire (nominal 110-220 volt) systems the neutral point of the winding shall be grounded.  (see App. G, Fig. 59.)

Two Phase Systems:
  In 3 wire systems the neutral point of one transformer winding shall be grounded; in 4 wire independent systems the neutral point of each winding shall be grounded independently.  (See App. G, Fig. 60.)

Three Phase Systems:
  In 3 wire delta systems the neutral point of one transformer winding shall be grounded; in 3 wire star and 3 wire T or Scott system the common point shall be grounded.  (See App. G, Fig. 61.)


C.    Grounds.

Transformer grounds of a conductivity not less than No. 6 A.W.G. copper wire shall be provided at any one of the following locations:


At the transformer pole.


At a pole adjacent to the transformer pole.


At load end of each service supplied from the transformer, separate from the usual house ground except that where three or more services are supplied from one transformer or bank of transformers, grounds at the two services nearest the transformer pole and one ground at services at approximately 500 foot intervals will suffice.


D.    Lead Wires.

Vertical leads between the circuit conductors and the transformers shall be installed in compliance with Rule 54.6-A, or where vertical leads are of open wire construction they shall comply with clearances required in Table 1, Cases 7, 8, and 9, and Table 2, Case 15 and where the distance between levels is in excess of 10 feet, additional supports shall be installed equidistant between the levels involved.  (See Rule 58.5-A.)


E.    Cut-Outs.

Cut-outs may be located on the side of the cross arm opposite the transformers so that they extend their full dimension into the working space, but shall not impair the climbing space.


F.    Ground Clearances.

Where it is necessary to locate transformers, such as large size street lighting or power installations, on poles or structures with bottom of the cases a minimum distance of 17 feet above the level of the ground, the lead wires carrying voltages in excess of 750 from line to transformers, other than those accessible to pedestrians only, shall be suitably insulated and installed in conduit.  All exposed energized parts shall be protected and guarded so as to afford the least possibility of contact.  Under no condition shall the lead wires be maintained at less than 20 feet above the ground.


Note    This Rule was modified by Supplement 1.  To see the changes made by supplement 1 click here.  This page contains the wording of the rule prior to Supplement 1.