Electrical Drying of Telephone Cable 



By L. G. WADE 



DRYING equipment has recently been installed at the Kearny 

 Works of the Western Electric Company whereby exchange area 

 telephone cable is heated to a temperature of 270 degrees Fahrenheit 

 by passing direct electric current through the copper wire conductors. 

 Before discussing this installation in detail, however, it might be well 

 first to outline the type of material handled and to review briefly the 

 history of telephone cable drying methods and the reasons for the 

 changes that have occurred. 



Telephone cable consists of a number of individual paper ribbon or 

 pulp insulated wires grouped together and the whole then covered 

 with a serving of wrapping paper before being sheathed in lead. 

 Cables may vary in length from a few feet up to several thousand 

 feet, and in number of pairs from 6 to 2121. The size of the wire 

 ranges from 26 American Wire Gauge to 10 American Wire Gauge, 

 with some of the product often containing as many as two or three 

 different sizes of wire in the same cable. One or more cable lengths 

 are wound on a core truck which may be readily moved from one 

 place to another by means of an electric truck. 



Early cables were textile insulated and then dried by placing the 

 cores in a heated oven, followed by boiling in a tank containing a 

 sealing mixture or impregnant. The impregnant was used to keep 

 the cable relatively dry in the rather imperfect lead sheath developed 

 at that time. However, with the advent of an improved lead sheath 

 extruded directly on the core, which would guarantee the excluding 

 of any water, it was found desirable to go to a dry paper insulated 

 telephone cable. This change in design reduced capacitance to about 

 one-half of the previous values. The paper insulated cable was dried 

 in a brick oven with gas retorts below a grille floor for maintaining the 

 oven temperature between 215 degrees and 250 degrees Fahrenheit. 



This method of drying produced satisfactory results for short-haul 

 cables in use at that time. However, with the possibility of longer lead 

 covered cable circuits replacing open telephone lines, it became neces- 

 sary to obtain a greater degree of dryness in order to meet the new 

 demand for transmission quality. The toll cables, which were for the 

 longer haul, were therefore given an additional drying after the 



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