Fig. 955.—One form of "come along." The wire is inserted between jaws and is held fast when tension is applied to the ring.
Fig. 956.—An improved form of "come along" or wire stretcher. The jaws which grip the wire are smooth and remain parallel in closing, thus the wire is not scratched or indented, as with circular jaws having teeth.
Ques. How much tension must be put upon the wires?
Ans. In applying tension to the wires as they are strung on the poles, it is the rule to allow some sag. The amount of sag to be allowed varies with different line hangers.
A typical case quoted by one or two authorities gives a sag of four inches at the center of each 130 foot span for a given size of wire, at a given temperature. A more general rule is to make the tension on a wire as it is drawn up between each pair of poles equal to one-third of its breaking weight. Thus No. 10 B.& S. gauge, would be drawn to about 163 pounds, and No. 12 to about 102 pounds. The temperature at the time of stringing and the distance between the poles are, however, important considerations in applying tension and allowing for sag. Thus, one construction company specifies a dip of 10 inches in summer and 8 inches in winter for spans of 130 feet, or 40 poles to the mile. Several authorities specify figures about as given in the above table for No. 14 iron or copper wire.
