Vulcanized Rubber insulated electric cables (v.r.i electric cables) Vulcanized rubber insulated cables: atural rubber is the coagulated latex of certain species of tress. Vulcanized rubber is posse's high insulating qualities, but the material absorbs moisture and deteriorates by rapidly oxidizing into a resinous substance. Therefore 3 to 5 % amount of sulphur is incorporated with the rubber; as a result, it becomes a imprevious to water, flexible and of high resistivity. This whole process is known s vulcanization and the product which is obtained is known as vulcanization rubber. This process is performed at 149 degree c and which is above the melting point of sulphur. It has a good mechanical strength, dependent upon its degree of vulcanization. When we use this type of cable in which place, where the heat and day light are not present, and the vulcanized rubber retains its physical properties for a long period. It is found that, it has a high specific insulation resistance and elastic, which is not present as high as that of pure rubber. The pure rubber is become soft when we use at high temperature, as a result in winter season it is hard and break down. Rubber has negative effects on copper conductor, therefore the copper conductors are tinned and then vulcanized rubber insulation is used. To prevent the weather affects a cover is used on the cable insulation. This is known as braiding. The braiding is affected by passing the cable through a machine, which makes a very tight and neat covering. The braiding may be of cotton, jute, glace cotton, silk or even of steel, copper, or phosphor bronze wire. The v.r.i cables are mostly use in surface and underground wiring system for domestic and industrial installation. The is composed of either natural or synthetic rubber mixed with modifying agents to gave it the desired mechanical and electrical properties.
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