PolytheneWhat is polythene? It is thermoplastic material used as insulator, and for many other purposes in communication industry. Polythene is mostly used in cases where a chemically-resistant plastic material is needed. It is a well-known fact that cables are classified as belonging to the main parts in the modern communication systems. Cables used for communication purposes differ in length, construction, properties, and, naturally, in their cost. Polythene cables belong to the type of cables widely used in transmitting electrical energy from area to area, since polythene is the popular and highly useful insulating material of today. Polythene cables are comparatively new devices. Their industrial production started only after World War II. Since that period they have been widely used in different spheres of energy transmission throughout the world. Polythene cables are known to have a number of advantages: they may be used for both a conductor insulation and a sheath, which makes them one of the most usable substance in industry. There exist two main types of polythene cables: the one having polythene insulation for the conductors, and the other having paper insulation. To these belong lead-sheathed paper-core cables. The number of pairs in different cables is also different. Of them the cables including 100 pairs and more have natural polythene sheaths. Unlike lead-covered cables, polythene ones can be laid directly in the ground without ducts since they are corrosion-proof, while lead-sheathed cables are usually laid in asbestos-cement ducts since they can be easily corroded. Another advantage of polythene cables is that they can be used in much longer length than lead-covered ones. The process of laying cables is known as "long-length cabling".
Ответьте на вопросы по тексту • What is polythene? • What do cables differ in? • What are the advantages of polythene cables compared with lead-sheathed ones? • Why can polythene cables be laid directly in the ground?
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