A New Type of Underground Telephone Wire 



By D. A. QUARLES 



A new type of telephone line is described in which a specially insulated 

 twin wire is plowed into the soil. Problems of wire design, splicing and 

 maintenance are discussed and transmission characteristics are given. 



IN this day of multi-channel transmission on open-wire lines, lead- 

 covered coaxial and multi-wire cables, and of radio and ultra-high- 

 frequency transmission without lines at all, it behooves the develop- 

 ment engineer concerned with line structures to be alert to advanced, 

 even to radical, ideas. Rubber insulated telephone wire placed 

 directly underground is a case in point. 



The urge to put telephone lines underground is only a littler younger 

 than the business itself. In large measure, this has been realized by 

 installing lead-covered cables in underground duct systems. An 

 alternative arrangement used more recently is spoken of as buried 

 cable} This is lead-covered cable, the sheath of which is protected 

 from corrosion by successive layers of paper and jute flooded with 

 asphalts. In addition, as a provision against mechanical injury or 

 interference from outside electrical sources, a steel tape armoring 

 is sometimes used. Where conditions have been favorable, the prac- 

 tice of burying suitably protected cables directly in the ground has 

 been applied both to toll and to large and small exchange area cables 

 and to one and two-pair entrance cables for underground service 

 connections. 



Because, with underground cables in conduits and with buried 

 cables, the costs essentially limit their use to those cases where appear- 

 ance is an important factor or where a considerable number of circuits 

 can be grouped under the same sheath, these methods are not generally 

 applicable to service on one or two circuit routes, such as those extend- 

 ing to remote subscribers, typical of rural distribution. Particularly in 

 the interest of providing a lower cost type of plant and thereby making 

 possible a more extensive development of service in rural communities, 

 it appeared there would be a considerable incentive for the develop- 

 ment of an inexpensive form of buried circuit. Such a circuit would ob- 

 viously require that an economical means of installation be devised 

 and even more important that the material used be serviceable for a 



> C. \V. Mier and B. D. Hull, Bell Telephone Quarterly, Volume 8 (October 1929). 



446 



