All About Electrical Cables and Wires Tutorials

A cable is a length of single conductor, generally with several wires stranded together, or two or more conductors, each provided with its own insulation and laid up together. The insulated conductors may or may not be provided with an over all protective converging. The conductor with its insulation but without mechanical protection is known as the core of the cable.
A cable consist of the following three parts.
1. Conductor: It provides conducting path of electric current.
2. Insulation: An electrical insulating medium that prevents direct contact or unsafe proximity between the conductor and other objects.
3. External protection: Protects against mechanical damage, chemical or electromechanical attact, free or any other deleterious external influences. Copper used on overhead lines is generally hard drawn for providing adequate mechanical  strength. However in case of cables, copper in annealed condition is used. Aluminum being lighter is extensively used in cables, However, joining of aluminum conductors calls for the use of special techniques and expertise.The size of conductor depends on the current rating of the conductor.Classification of Cables based on Insulation:On the basis of insulation, the cables are classified as under: Paper insulated cables:  In these cables paper is wound on the conductor in successive layers to achieve the needed dielectric strength. Such cables are manufactured in various sizes from 5 mm squared to 500 mm squared cross-section of conductor and voltage ratings up to 33kv.The cable are provided with steel armour made up of galvanised steel wires or shielding tap. The outer sheath on the cable provides protection against external forces on the cable. The metallic shielding around the conductor is used to control the electrostatic voltage stress, reduce corona effect and to decrease the thermal resistance. Metallic shielding in only 3 to 5 mm thick. Lesser thickness reduces circulating currents and power loss.