The copper cables were so strung as to have a minimum distance from the ground of 25 feet at the lowest points of the spans. In order to do this the standard steel towers that hold the lower cables 40 feet above the ground level at the insulators are spaced at varying distances apart, according to the nature of the ground between them. At each tower the upper cable of each circuit is 5 feet 3 inches higher than the two lower cables, and this distance between the elevations of the upper and the lower cables is maintained whatever the amount of sag at the centre of each span. If there is a depression between two standard towers on a straight portion of the line, the sag in the centre of a span 400 feet long may be as much as 18 feet. Where a rise and fall in the ground between towers make it necessary to limit the sag to 14 feet in order to keep the lowest cables 25 feet above the highest point of earth, the length of span is limited to 350 feet. If the rise and fall of ground level between towers allow a sag of only 11 feet with the lowest cable 25 feet above the earth, the length of span with 40-foot towers is reduced to 300 feet; and if for a like reason the sag is limited to 8 feet, the span may only be 250 feet.

Fig. 105.—Take-up Arrangement on Terminal Tower.

At each terminal tower, where the cables are secured before they pass into a terminal-station, the three insulators for each cable are in a straight line with their centres, 30 inches apart. When a line cable reaches the first insulator of the three to which it is to be attached on one of these towers, it is passed around the neck of this insulator and then secured on itself by means of two clamps that are tightened with bolts and nuts. See [Fig. 105]. The cable thus secured turns up and back over the tops of the three insulators and goes to the terminal-station. Around the neck of the insulator to which the line cable has been secured in the way just outlined a short detached length of the regular copper cable with the parts of a turnbuckle at each end is passed, and this same piece of cable also passes around the neck of the next insulator in the series of three. By joining the ends of the turnbuckle and tightening it, a part of the strain of the line cable in question is transferred from the first to the second insulator of the series. In the same way a part of the strain of this same line cable is transferred from the second insulator of the series to the third, or one nearest to the terminal-station.


INDEX.


Transcriber’s Notes