Cable is assembly of two or more than two conductor in running side by side or bundled form. It is used in building wiring and used in industry and commercial places to aim of transmit power or signal from one to another, and it is very important to install wire of good quality otherwise it would burn down. It is very careful about selection of cable according to requirement. There are many types of cable that are found in market according to use like there are also communication cable used to transmit low power signal and for uses of electronic signal purposes and Fiber optical cable used for optical data through light source to receiving devices and the cable which is used to transmit electric power is called Power cable.
- Basic parts of power cable: –
Copper and aluminum are used as a conductor material in cable because of higher electrical conductivity solid or number of bare wires either made up of aluminum or copper to make a power cable.
The number of wire strands in conductors are 7, 19,37,61,91 etc. The size of conductor is represented by 7/A, 19/B, 37/C and so on, in which first represent the number of strands and second represent like A, B, C, represent diameter of individual wire in cm or mm.
Most used insulator in cable like insulated like poly vinyl chloride, impregnated paper, butyl rubber, cross linked polythene but paper insulated cable is preferred because of their high current capacity and generally reliable and having a long life.
The insulator must have following properties: –
- It must have high resistance so that it does not allow current flow in it.
- It must have high dielectric strength so that it does not allow any leakage current.
- It has high mechanical strength so that there is less chance of breakdown
- It must be capable of operating at high temperature
- It should have low thermal resistance.
- It should have low power factor.
- Inner Sheath
It basically used for protecting the cable from moisture because moisture evaporate the property of insulation. It made of lead alloy, and these strengths withstand the internal pressure of pressurized cables. The material should have nonmagnetic material in inner sheath. In power cables there is an aluminum sheath is used because it is cheaper, smaller in weight and high mechanical strength than the lead sheath.
When there is an underground cable then protection from corrosion or electrolyte we use material like hessian or PVC.
Armouring is done by galvanized steel wire, or two layer of metal type are applied over sheath for protecting it from mechanical damage. The steel wire nis normally used because it has high longitudinal strength.
It gives the mechanical strength to cables. It protects from all over damage like moisture, corrosion, dirt, dust and so on. The thermoplastic material is used making over sheath.
- Types of Cable
- Ribbon Electric Cable
It consists of multiple insulated wiring running parallel with one another and used for multiple data transmission like this is used to connect the CPU with motherboard. And are generally used for interconnection of networking device.
- Shielded Cables
It consists of one or two insulated which are covered by a woven braided shield or aluminium foil for better signal transmission and removing irregularities in frequency and power and external interference in radio. These cables are also used to transmit high voltage and are protected by shield.
- Coaxial Cable
It consists of solid copper or steel conductor plated with copper which is enclosed in the metallic braid and metallic tape. This is entirely covered by with an insulated protective outer jacket. These types of electric cable are used for computer networking and audio video networking. It is used in telephone trunk line, broadband internet, high speed computer data busses, cable television and connecting radio transmitter.
- Twisted Pair Cables
It has two or more insulated copper wires which are twisted with each other and are colour coded. These are used in telephone cable and resistance to external interference can be measured by number of wires.
- Fiber Optical Cable
These types of cable are used to transport optical data through light source to the receiver. It is assembled similar to electrical cable but containing one or more optical fibre that are used to carry light. These optical fiber elements are typically individual coated with plastic layer and contained in protective tube suitable for environment
- Instrumentation Cable
These are flexible and shielded cables for transmission of signal between equipment in industrial installation. Especially suitable for optimum data transmission with high level of electromagnetic interference.
- Underground Cable
Underground cables are employed to transmit and distribution of electrical power where there is impractical to use overhead transmission line, or this is used in congested area where there is impossible to use overhead transmission line. There are kind of cable used depend upon voltage level and service requirement. Underground cable consists of a central core or more than two or three core made of copper or sometime uses of aluminium and insulated from each other by impregnated paper and metallic sheath is provided to protect insulation from moisture.
Types of cable used in any particular location depend upon its mechanical strength and voltage level.
According to voltage level, there category can be divided.
Types of cable
Low voltage cable
Up to 1KV
High voltage cable
Up to 11KV
Super tension cable
Up to 33KV
Extra high-tension cable
Up to 66KV
Extra super voltage cable
Up to 132KV
- Selection of Cable
For consideration of cable for correct size and for type of application, some factor to be considered such as following:
- System voltage
- Current carrying capacity
- permissible voltage drop
- Short circuit rating