Insulation of Telephone Wire With Paper Pulp

I N 1887 the leading telephone engineers attempted to standardize telephone cables and specifications, finally deciding upon # 18 B & S gauge wire covered with two wrappings of cotton and twisted into pairs. A maximum cable size of 52 pairs in a two-inch diameter cable sheath 97% lead, 3% tin, and thick was permitted under the specifications. The grounded capacity of such cable was 0.20 mf. per mile. In 1891 the Western Electric Company had made successful application of manila rope paper as insulating material for dry core cable and by drying this paper immediately before covering with lead by the newly developed extrusion process the core could be kept dry without the old impregnation with hot paraffin. A great improvement in electrical properties resulted from this change, the electrostatic capacity dropping to approximately one-half its former value. The use of manila paper made from old rope from this time on grew in use for insulating purposes (Fig. 1). The telephone demand was increasing all the time, and since the supply of old rope depended in a large measure on maritime sources of supply the price began to increase. Improvements in telephone instruments, together with increased demand for telephones, permitted the use with economy of more and more pairs of finer and finer wires in a given diameter of cable. This trend can be readily seen if we follow the change in maximum number of pairs used at different dates. In 1888--50 pairs of 18-gauge wire were used, 1896--180 pairs 19-gauge, 1912--909 pairs 22-gauge, 1914--1212 pairs 24-gauge, 1928-- 1818 pairs 26-gauge, and in 1939--1515 pairs 24-gauge and 2121 pairs 26-gauge (Fig.