Insulation of Telephone Wire with Paper Pulp* 



By J. S. LITTLE 



A method has been developed for economically manufacturing in- 

 sulated wire for telephone exchange area cable by making the paper 

 on the wire. Further, this method his made it possible to increase the 

 number of wires in a full sized cable by 175% over the number in use in 

 1914. Developments now under way indicate that suitable insulation 

 can be made to replace certain textiles in some classes of wire and 

 that the use of this process may therefore be still further extended in 

 the not so distant future. 



Introduction 



IN 1887 the leading telephone engineers attempted to standardize tele- 

 phone 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 West- 

 ern 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. 2). The increasing number of wires demanded thinner and 

 thinner and better and better paper. As the cable demand increased, 

 increased insulating speeds were necessary to aid in keeping down the cost 

 * Reprinted, with minor changes, from Wire and Wire Products, October 1939. 



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