Original General Order
Detailed Construction Requirements for Supply Lines
(Class H, L
and T Circuits)
54.9 Low Voltage Racks, 0-750 Volts
Conductors of not more than 750 volts may be attached to poles by means of vertical racks of insulators or individual supports in rack configuration and, where so attached, the following rules shall apply.
B. Pole Arrangement and Clearance
(1) Clearance From Poles: Conductors of 0-750 volts in rack construction may have clearances less than 15 inches from center line and 3 inches from surfaces of pole, as specified in Table 1, Column D, Cases 8 and 9, respectively, but shall have a clearance of not less than 2 ½ inches from the surface of pole. (For interpretation of this 2 ½-inch clearances see Appendix G, Figure 60.)
Arrangement: Not more than 7 conductors of not more than 2 circuits shall be
attached to any pole in a continuous rack group. In a rack group the conductors shall be of one ownership and the
vertical separation between line conductors attachments shall be uniform.
Conductors, both line and service drop, in rack configuration shall not be attached to more than 2 sides (there being 2 sides) of any pole at the level of any one rack group. Climbing space in conjunction with these attachments shall be maintained as specified in Rule 54.9-F.
C. Conductor Material
All conductors of a rack group in the same vertical plane shall be of the same material.
(1) Urban Districts: Conductors in rack construction in urban districts shall have a crossing not less than the equivalent of double braid weather-resistant covering.
(2) Rural Districts: Line conductors in rack construction in rural districts may be bare conductors provided the vertical separation between conductors is not less than 12 inches and conforms to the requirements of Rule 54.9-D where greater separation is specified.
D. Conductor Spacing and Span Length
The vertical separation between conductors supported as a group in rack construction shall be not less than the following for span lengths as indicated:
Length of span (feet)
Vertical separation (inches)
150 or less
200 or less but more than 150
330 or less, but more than 200
More than 330
E. Vertical Clearance Between Conductor Levels
A vertical clearance of not less than 6 feet shall be maintained between the top conductor supported in rack construction at one level and conductors supported on the same pole at the next level above except as provided in Rule 54.4-C6 for lead wires and as modified:
(1) With Guard Arm Below Conductors of 750-20,000 Volts: The vertical clearance between the top conductor in a rack group and conductors of 750-20,000 volts at the next conductor level above, may be less than 6 feet but shall be not less than 4 feet. If a clearance of less than 6 feet is used, all of the following requirements:
A wood guard arm not less than 48 inches long shall be installed directly above and parallel to the top line conductor of such a rack group;
Conductors in such a rack group, which are so guarded, shall not be attached to more than one side (there being four sides) of any pole; and
No service drop conductors supported on such rack shall pass between the surface of pole and the vertical plane of the line conductors. Any service drop conductors attached to and supported by the line conductors shall have a clearance of not less than 15 inches from surface of pole. (See App. G, Fig 43.)
Each guard arm and its pole attachments are required by Rule 46 to withstand a vertical load of 200 pounds at either end.
(2) With Guard Arm Below Conductors of 0-750 Volts: The vertical clearance between the top conductor in a rack group and conductors of 0-750 volts at the next conductor level above may be less then 6 feet but shall be not less than 4 feet. If a clearance of less than 6 but shall be not less than 4 feet. If clearance of less than 6 feet is used, a wood guard arm not less than 48 inches long shall be installed directly above and parallel to top line conductor of such a rack group.
(3) Under a Transformer: No guard arm will be required over line or service drop conductors attached in rack construction to the surface of a pole directly below a transformer installation provided that at that level all attachments to the pole shall be approximately in the vertical plane through the center lines of pole transformer installation and no conductor so attached makes an angle greater than 60degrees with that plane. The top conductor so supported shall have a vertical clearance of not less than 48 inches below the level of conductors on the hanger arm; a vertical clearance not less than as specified in Rule 54.4-C6 below the lowest point of the drip loop of primary leads to the transformer; and a vertical clearance of not less than 10inches below the lowest part of the transformer case hangers. (See App. G. Fig. 33.)
(4) In Rural Districts: In rural districts (see definition, Rule 21.0-B) where one circuit only of 7500-20,000 volts is supported on the poles above conductors in rack construction, the vertical clearance between the top conductor in rack construction and the nearest 7500-20,000 volt conductor level may be less than 6 feet but not less than 4 feet and no guard arm is required.
(5) Related Rack and Crossarm: Where conductors supported in rack construction are connected to conductors supported on a crossarm on the same pole, the vertical clearance between the level of conductors of 0-750 volts on the crossarm and the nearest conductor in rack construction shall be no less than 2 feet and climbing space shall be maintained in the same quadrant or on the same side of pole through both conductor levels in accordance with climbing space requirements in Rule 54.7 and 54.9-F. This provision is not applicable where the crossarm is a combination arm.
F. Climbing Space in Rack Construction (See App. G, Fig 32)
A climbing space shall be maintained through the levels of conductors supported in rack construction and for a vertical distance of not less than 4 feet above the top conductor and not less than 4 feet below the bottom conductor so supported.
The width of the climbing space measured horizontally through the center line of pole shall be not less than 5 inches plus the diameter of the pole ant the extremities of such width shall be equidistant from the center line of pole. The depth of the climbing space shall be not less than 30 inches measured perpendicularly to this climbing space boundary through the center line of pole. The width of the climbing space, perpendicular to and at the extremity of this 30-inch depth dimension, shall be not less than 38 inches and neither of the other two side boundaries shall make an angle of less than 90 degrees with the boundary through the center line of pole. (See App. G, Fig. 32)
The position of the climbing space through the levels of conductors in rack construction shall be related to climbing spaces through the levels of conductors on crossarms in accordance with the requirements of Rule 54.7-A. The climbing spaces through the levels of conductors of two or more rack groups which are separated less than 6 feet shall be maintained in the same quadrant or on the same side of pole.
Guys vertical conductors attached to the surfaces of poles, and terminals, which are listed in Rule 54.7-A4 as allowable climbing space obstructions, are not permitted in climbing spaces through conductors in rack construction.