mechanically continuous metal conduit and sheathing or of tile, concrete, or similar material. In all cases the interior and all outlets must be smooth. In damp locations where conductors are not moisture proof metal sheathed, runways shall be waterproof and provided with drainage for condensation. Conductors carrying over 750 volts must always be provided with metal sheathing and be run in conduit unless separately supported and isolated, or otherwise guarded. Multiple conductors, if in conduit, shall have potheads or equivalent outlets to protect against moisture or electrical strains. (153, 154, 313, and 314.) 33. Temporary wiring, when not installed to conform to these rules, must be under constant supervision and guarded by suitable barriers and warning signs. (156 and 319.) Grades of Construction for Overhead Lines. For convenience in connection with these rules electrical lines are divided into the following classes: Grade A. Includes supply lines over important railways, constant-potential alternating-current supply lines of over 7,500 volts, constant-current circuits exceeding 10 amperes, direct-current grounded trolley circuits of over 750 volts where at higher levels and crossing over or conflicting with, or on common supports with signal lines. Grade B. Includes (1) supply lines over unimportant railways, (2) constant-potential alternating-current supply lines of between 5,000 and 7,500 volts, or constant-current circuits between 7.5 and 10 amperes, where at higher levels and crossing over or conflicting with, or on common supports with signal lines, (3) in general circuits over 7,500 volts in urban districts involved in crossings with other supply circuits. Grade C. Includes (1) constant-potential alternating-current supply lines between 750 and 5,000 volts, or constant-current circuits not over 7.5 amperes, where at higher levels and crossing over or conflicting with or on common supports with signal lines, and (2) in general circuits between 750 and 7,500 volts in urban districts involved in crossings with other supply circuits, and in general (3) supply lines above 7,500 volts in rural districts at higher levels and crossing over, or conflicting with, or on common poles with supply lines not exceeding 750 volts. Grade D. Signal lines over important railways. Grade E. Signal lines over unimportant railways. Strength of Line Conductors. 34. In any case where two or more of the above conditions exist, the grade of construction shall be the highest called for under any condition applying. Where lines of different classification cross each other, or are in conflict, or are on the same supports, the higher voltage circuits shall be carried at the higher levels, or the circuits at higher levels made to conform to the strength requirements of the higher voltage classification. (210, 214, 280.) 35. All supply conductors shall be of material which will not corrode excessively. Aluminum or steel reinforced conductors shall be stranded. No wire smaller than No. 6 if soft copper, No. 8 if hard or medium copper, or less than No. 9 (steel wire gage) if steel, shall be used in urban districts on spans not exceeding 150 feet, except as noted herein. Larger sizes are required for longer spans. Services shall not be less than No. 10 if soft copper, No. 12 if hard or medium copper, or less than No. 12 (steel wire gage) if steel. is permitted for grades A, B, C, and D, and No. 12 for grade E when the sags are not less than 12 inches for spans not exceeding 100 feet and when the sags are not less than 18 inches for spans not exceeding 125 feet. No. 9 for steel is permitted and No. 8 for hard or medium copper for grades A, B, C, and D, and No. 10 for grade E when the sags are not less than 27 inches for spans not exceeding 150 feet. In urban districts supply service leads shall also conform to these requirements. (221, 273, 280.) No. 10 hard copper or steel 36. Conductors and supports shall be designed to withstand the resultant loading at 0° F., due to the weight of the conductor plus the added weight of a layer of ice inch in radial thickness, combined with a transverse horizontal wind pressure of 8 lbs. per square foot on the projected diameter of the ice-covered conductor. (222.) 37. In general, copper conductors shall have norinal sags as Learly as practicable to the following: FOR GRADES A, B, AND C. Sags at 60° F. for Medium and Hard-Drawn Covered Copper Wires. FOR GRADES A, B, AND C. Sags at 60° F. for Soft-Drawn Covered Copper Wires. FOR GRADES A, B, AND C. Sags at 60' F for Medium and Hard-Drawn Bare Copper Wires. 38. Poles and towers shall be designed with a factor of safety of 2 (except for 8 inch or larger tops where a factor of 1 is allowed) to withstand, in addition to the loaded conductors, the horizontal wind pressure at right angles to the direction of the line, of 12 lb. per square foot of projected area for grade A, 7 lb. for grade B, and 4lb. for grade C. For grades A and B wooden poles must be replaced or reinforced when their strength decreases to two thirds the above, and for grade C when one half the above. Wooden poles must be free from defects and at least 7 inches in diameter at the top for grades A, and 6 inches for grades B and C. Additional strength shall, when desirable, be provided by guys or braces. (230, 235, and 251.) 39. Crossarms for grades A, B, or C construction shall be the equivalent of yellow pine or fir, with the following minimum dimensions: A and B, 2 or 4 pin, 3x4 inches; 6 or 8 pin, 31x41 inches; C, 2 or 4 pin 24 by 33 inches; 6 or 8 pin, 3x4 inches. In all such grades of construction the crossarms must have sufficient strength and bracing to withstand, without change of po sition, all stresses to which they are normally subjected including linemen on them, with a limit of unbalanced tension where conductor pulls are normally balanced, of 700 lb. at the outer pin. Pins, ties, and other fastenings shall have sufficient strength to withstand 700 lb. per pin or fastening. Crossarms for grade D shall have a minimum section of 24 x 32 inches for 6 foot arms or shorter and 3x4 inches for longer arms, and shall be double on the crossing poles. For grade E single arms 3x4 inches are permitted, smaller arms must be double: Wood pins for grades D and E shall be sound and straight grain, with a minimum diameter of shank of 14 inches and a maximum length of 84 inches. (231, 280, and 281.) Signal Lines Over Railroad. 40. Signal lines crossing railroads shall have the crossing span as short as practicable, preferably not exceeding the normal span of the line. No crossing span should exceed 150 feet in length, if this can be avoided. Whenever practicable, the difference in elevation of the wire supports at the crossing poles and the poles adjacent shall not be greater than 5 feet. The poles supporting the crossing span shall be head-guyed away from the crossing span and side-guyed in each direction. The number and size of guys for signal lines shall be not less than given in the following table, and for spans longer than 150 feet shall be proportionately increased. Number of Wires in 1 to 10 11 to 20 21 to 40 41 to 60 61 to 80 Head and Side Guys Required (in Each Direction). One 10,000-pound cable. One 6,000-pound cable It is recommended that head guys should be anchored at a distance from the pole not less than the height of the attachment. Side guys should be anchored at not less than one third this dis tance. 41. The following table gives the minimum sizes for grade D construction galvanized steel strand messenger cable to be used for supporting different sizes of signal cable: |