Polyethylene Insulated Telephone Cable

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 telephone 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 desired. electrical properties is discussed. In a broad sense this article may be considered, as announcing an important new insulating material for telephone cables which may be expected eventually to have very extensive applications 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 b u t in the case of either ribbon or pulp insulation a considerable amount of air is included in the electric field surrounding the conductor so t h a t 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 competitors of paper, and polyethylene in particular now appears to have an important field of application.