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pairs, the bunch being encased in a lead sheath about 3 inch thick, as shown in Fig. 89. The pairs are twisted to overcome inductance; and to distinguish between the conductors of a pair the insulation on one of them is usually marked in some peculiar way. Specifications for dry-paper cables call
for a capacity between conductors of not over 0.08 microfarad (see Appendix) per mile; a conductivity of not less than 98 per cent. that of pure copper; an ohmic resistance of not more than 47 ohms per mile at a temperature of 60° F.; and an insulation resistance of each conductor of at least 500 megohms (see Appendix) per mile. Cables
are thus made containing from 5 to 300 pairs of conductors in lengths of 800 and 1,000 feet. A 200-pair cable of No. 19 wires has an outside diameter of only about 2 inches. Iron wires are never formed into telephone cables.
Stringing the Cable is done by first fixing clamps n, Fig. 90, to the sides of the poles a short distance below the cross-arms. A suspension cable c, usually composed of 7 strands of galvanized steel wires, is then run from clamp to clamp and bolted in place as indicated. The cable and reel as received from the manufacturer are next mounted at one end of the line, as shown at m, Fig. 91, and by means of a manila-hemp rope r, Fig. 92, secured to the free end of the cable and led through pulleys a temporarily fastened to the poles just below. the suspension clamps, and terminating in a windlass h mounted at a distance along the line from the reel equal to the length of the cable on the reel, the cable is pulled in position. An iron cap c, Fig. 93, screwed to the end of the cable sheath, facilitates the fastening of the pulley rope. The windlass is operated by horse-power as shown. When all the cable on one reel has been strung, the process is repeated, the next reel being set up at the terminus of the first length. Such a case is illustrated in Fig. 91.
Cable Hangers are attached to the cable as the latter is drawn off the reel, and, as the cable is pulled along, the hangers slide over the suspension cable the end of which is temporarily lowered on
a level with the reel as in Fig. 91. One form of cable hanger is shown in Fig. 94 at a ce. It consists of a hook and one hemisphere a, a vertical
Fig. 93.-A Convenient Device for Fastening the Pulling
Rope to the Cable
extension and hemisphere c, and a steel ring e. The two hemispheres are of galvanized iron; they are placed on each side of the cable n, the ring is
Fig. 94.—A Cable Hanger, and the Tongs Used to Adjust
It in Position
slipped down over the hook, and by means of the tongs m the ring is forced into place,