Зображення сторінки
PDF
ePub

TELEPHONE LINE WIRING

The Route to be taken by the telephone lines is governed by the location of the stations to be connected, and by the streets, roads, or alleys along which rights of way can be obtained. The shorter the line and the straighter its course, the better. Rights of way must generally be secured by dealing individually with each property owner on whose land poles are to be placed. The agreements thus made should be in writing and should state with reference to a sketch the number and location of poles to be erected, braced or guyed, and the extent to which tree-trimming can be carried. These matters should be settled definitely before beginning the construction of the pole line.

The Pole Line consists of poles set in line along the route chosen. Each pole carries one or more cross-arms or brackets near its top, and each crossarm usually carries from 6 to 10 glass insulators supported on wooden pins. The line wires are tied to the insulators and run parallel with each other from pole to pole. When the line consists of less than 6 wires, brackets fastened to the sides of the poles are generally used in place of crossarms for supporting the insulators. When the

line consists of more than 15 complete circuits, that is, more than 3 10-pin cross-arms can carry, a 50-pair cable is suspended between the poles, and the cross-arms are used for further growth.

The Location of the Poles according to the rightof-way agreements should at first be indicated by stakes driven in the ground at uniformly equal distances of 130 feet. This spacing will require 40 poles per mile of line. At curves and at railway and stream crossings, however, the spacing may have to vary so as to conform to the existing conditions and afford the proper strength and alignment. Along railway lines the poles should not be set within 7 feet of the edge of the rails, and the line wire must be at least 22 feet above the top of the rails. In crossing roads, streets, or highways the vertical distance between ground and wire should be at least 18 feet, and the crossing should be made at an angle of 45 degrees.

In crossing hilly country the shortest poles should be used on high ground and the longest poles in the valleys, as in Fig. 63. The intermediate poles should be of such lengths that the difference in height between adjacent ones will not tend to lift any of the insulators off their pins; in Fig. 64 such a tendency exists at a. The smoothest and best proportioned poles should be reserved for use in front of residences, and the heaviest poles for the corners and curves.

Telephone Poles.-Chestnut, southern cedar, and Norway pine are the woods now chiefly used for

telephone poles. The timber should be cut in the winter months, from December to February, when the sap has left the trees and growth is temporarily suspended. The presence of sap in a

FIG. 63.-Proper Distribution of Poles in Hilly Country

pole causes it to rot quickly. Each pole should have not more than one bend nor a sweep of over 12 inches; it should be closely grained, free from large knots, and its heart must be sound and firm. The bark and branches should be removed and the pole cut to the required length as soon after it has been felled as possible. The required length depends upon the number of cross-arms it must

a

FIG. 64. When Poles All of the Same Lengths are Used in Hilly Country, Some of the Insulators May be Lifted Off their Pins

carry and the obstacles to be cleared by the wires. With cross-arm, the pole must be at least 15 feet above ground and at least 5 feet in the earth, so 20-foot poles are the shortest ones practica

ble. Longer poles usually vary by 5 feet upward to 70 feet and are buried from 6 to 8 feet in the earth. The circumference at the top of the pole and at 6 feet from the butt must be considered in selecting poles. These dimensions should be proportional to the length of the pole and should approximate those given in the following table for poles from 20 to 70 feet long:

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

The top of each pole should be slightly pointed as in Fig. 65 and then painted to enable it to shed water. A number of gains n should be cut in the pole, corresponding to the number of cross-arms to be used. The center of the first gain should be 10 inches from the top of the pole, and the center of each subsequent cut should be 24 inches below that of the preceding one. The gains should each be 3 inches wide and inch deep, true and square with the axis of the pole so that the

cross-arms when fitted in them will be at right angles to the pole in all directions. Each gain should be bored for one §-inch bolt, directly through the center of the pole and at right angles to the gain, and should be painted to protect it from moisture. A paint well adapted for the top and gains of a pole is Prince's metallic paint, mixed in the proportion of 7 pounds of the dry paint to

[merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][ocr errors][ocr errors][ocr errors][merged small][merged small][merged small][merged small][merged small]

FIG. 65.-Telephone Pole Top Equipped with Cross Arms, Braces, Pins, and Insulators

I gallon of linseed oil. Two thick coats of this paint should be applied.

In Setting Poles a hole for each one is dug in the ground to a depth of 5 to 8 feet, depending on the height of the pole and the condition of the ground. When the ground is of normal consistency, the depths noted in the table just given are considered proper for straight lines; on corners

« НазадПродовжити »