On the straight portions of the line the steel towers are regularly erected 400 feet apart, but on curves the distances are less between towers, so that their total number is about 1,400 for each line. Standard curving along the line requires towers placed 50 feet apart, and a change in the direction of not more than ten degrees at each tower, except at the beginning and end of the curve, where the change in direction is three degrees. When the change in the direction of the line is not more than six degrees, the corresponding spans allowed with each change are as follows:
| Degrees change. | Feet of span. | |
|---|---|---|
| 1⁄2 | 300 | |
| 1 | 286 | |
| 1 | 1⁄2 | 273 |
| 2 | 259 | |
| 2 | 1⁄2 | 246 |
| 3 | 232 | |
| 3 | 1⁄2 | 219 |
| 4 | 205 | |
| 4 | 1⁄2 | 192 |
| 5 | 178 | |
| 5 | 1⁄2 | 165 |
| 6 | 151 | |
At some points along the line conditions require a span between towers of more than 400 feet, the regular distance for straight work. One example of this sort occurs at Twelve-Mile Creek, where the stream has cut a wide, deep gorge in the Erie plateau. At this point the lines make a span of 625 feet between towers.
Fig. 94.—Transposition Tower (Second Tower).
Fig. 95.—Elevations and Plan of Tower.
[Larger elevations and plan] (70 kB)
![[Larger elevations and plan]](#6023310579030268285_illo320lg.png.id-230917846399163047.wrap-0.html.html){kind=link}
The regular steel tower used in this transmission measures 46 feet in vertical height from its foot to the tops of the lower insulators, and 51 feet 3 inches to the tops of the higher insulators. The lower six feet of this tower are embedded in the ground, so that the tops of the insulators measure about 40 feet and 45 feet 3 inches respectively above the earth. At the ground the tower measures 14 feet at right angles to the transmission line and 12 feet parallel with it. The width of each tower at the top is 12 feet at right angles to the line, and the two sides having this width come together at points about 40 feet above the ground. Between the two L bars thus brought nearly together, at each side of a tower a piece of extra heavy 3-inch steel pipe is bolted so as to stand in a vertical position. Each piece of this pipe is about 31⁄2 feet long and carries a steel insulator pin at its upper end. The two pieces of pipe thus fixed on opposite sides of the top of a tower carry the two highest insulators. For the other four insulators of each tower, pins are fixed on a piece of standard 4-inch pipe that serves as a cross-arm, and is bolted in a horizontal position between the two nearly rectangular sides of each tower, at a point two feet below the bolts that hold the vertical 3-inch pipes, already named, in position. Save for the two short vertical and one horizontal pipe, and the pins they support, each tower is made up of L-shaped angle-bars bolted together. Each of the two nearly rectangular sides of a tower consists of two L bars at its two edges, three L bars for cross-braces at right angles to the edges, and four diagonal braces also formed of L bars. The lower halves of the L bars at the edges of each side of a tower have sections of 3″ × 3″ × 1⁄4″, and the upper halves have sections of 3″ × 3″ × 3⁄16″. This last-named cross-brace and the other two cross-braces have a common section of 2″ × 11⁄2″ × 1⁄8″. For the lower set of diagonal braces the common section is 21⁄2″ × 2″ × 1⁄8″, and the upper set has a section of 2″ × 11⁄2″ × 1⁄8″ in each member. At the level of the lowest cross-braces the two rectangular sides of a tower are tied together by one member of 2″ × 11⁄2″ × 1⁄8″ of L section and at right angles to the sides, and by two diagonal braces of 5⁄8″ round rod between the corners of the tower. On each of its two triangular sides a tower has four horizontal braces and three sets of diagonal braces. The two upper horizontal braces are of 2″ × 11⁄2″ × 1⁄8″ L section, and the lowest is the same, but the remaining horizontal brace has a section of 21⁄2″ × 2″ × 1⁄8″. Bars of 2″ × 11⁄2″ × 1⁄8″ L section are used for the two upper sets of diagonal braces, and bars of 21⁄2″ × 2″ × 1⁄8″ for the lower set. In addition to the cross-braces named, each triangular side of a tower near the top of the corner bars has two short cross-pieces with the common L section of 31⁄2″ × 31⁄2″ × 5⁄8″, one just above and the other just below the cross-arm of 4-inch pipe to hold it in place. At the bottom of each of the four corner bars of a tower a foot is formed by riveting a piece of 3″ × 1⁄4″ L section and 15 inches long at right angles to the corner bar. On one corner bar of each tower there are two rows of steel studs for steps, one row being located in each flange of the L section. On the same flange these steps are two feet apart, but taking both flanges they are only one foot apart. Every part of each steel tower is heavily galvanized.
