Polyethylene Insulated Telephone Cable 



By. A. S. Windeler 



(Manuscript received August 25, 1953) 



The physical properties of polyethylene are such as to make it attractive 

 for many wire insulating applications, particularly in multi-conductor 

 communications cables. This article presents certain factual information 

 relating to new types of multi-conductor cables having extruded polyethylene 

 insulation, and describes briefly their initial installation in working tele- 

 phone plant. The literature is replete with information on the physical and 

 chemical properties and the behavior of polyethylene, so no attempt is 

 made to explore the quality of the material per se. Polyethylene insulation 

 extruded in the form of both solid material and foam to impart certain de- 

 sired electrical properties is discussed. In a brood sense this article may be 

 considered as announcing an important new insulating material for tele- 

 phone cables which may be expected eventually to have very extensive ap- 

 plications in the Bell System plant. 



From almost the beginning of the art, multiconductor telephone 

 cables have been insulated with paper, applied as a helical tape or laid 

 down directly on the conductor in the form of pulp. Solid paper has a 

 dielectric constant in the order of 2.5 to 3.0 but in the case of either 

 ribbon or pulp insulation a considerable amount of air is included in the 

 electric field surrounding the conductor so that the composite effective 

 dielectric constant is of quite low value, usually about 1.5 to 1.6 in a 

 typical design. In recent years, as various plastics and other polymeric 

 materials have become available, these have been studied as competi- 

 tors of paper, and polyethylene in particular now appears to have an 

 important field of application. Polyethylene appears attractive because 

 of its excellent electrical properties including low dielectric constant 

 and power factor, compared ^vith other useable plastics, and high di- 

 electric strength. It is also highly impermeable to water or water vapor 

 and is available in the desired quantities at a reasonable price. Addi- 

 tionally it is considered probable that the long term price trend will be 

 downward. 



1245 



