Students - Frequently Asked Questions
Cables and the supply of electricity can seem like a complicated topic to understand. The ins and outs of how electricity is generated and works to provide us with the conveniences we are all accustomed to and the role cables play in this can be found below.
A traditional cable has three main components.
- Conductors – a conductor is used to carry the current (the flow of electricity) through the cable. Conductors are made of copper or aluminium and a number of conductors may be required in the one cable (multicore cables). The size of the conductor used reflects the amount of power, or current, the cable is capable of carrying.
- Insulation – the insulation in a cable is designed to cater for the voltage level of the cable, ie. the higher the voltage of the cable, the thicker the insulation needs to be. All conductors in the one cable are insulated with the same material. The insulation material can be constructed from a wide range of materials, including PVC (Polyvinyl Chloride), PE (Polyethylene), XLPE (Cross-linked polyethylene), EPR (Ethylene Propylene Rubber), CPE (Chlorinated Polyethylene) Paper.
- Protection – the cable requires protection from the environment in which it is to operate. This can take the form of a metallic shield such as Lead or Steel Wire Armour, or a polymeric such as PVC, HDPE (High Density Polyethylene) or Rubber.
Cable manufacturing these days is a far more automated process than in the past. Below is an outline of the manufacturing process for standard building wire cables.
The process begins with the conductor, which is usually copper. The copper wire will go through a process called drawing, where the copper strands which form the cable are made thinner. The wires are stranded and then taken to extrusion for insulation.
Depending on the cable design being manufactured, the insulated cores are layed-up and than again taken to extrusion for sheathing. Some cables will have additional layers added, such as nylon for termite protection, or armouring for mechanical protection.
The completed cable is tested for electrical performance, and then sent to packaging. In the case of small flat cables they are automatically wound onto spools, palletised and despatched. Larger cables are wound onto drums of varying sizes.
For a diagrammatic explanation of the cable making process, please refer to the PDFs below.
Electricity is one of the cleanest forms of power and an essential part of our lives. In order to generate electricity, other energy sources are used, for example:
- Coal, gas, oil, waster and nuclear fusion are converted into steam and then into electricity via conventional rotating plants.
- Water, wind and tidal energy are directly converted to electricity via rotating plants.
- Sunlight is converted directly to electricity via solar panels.
Distribution of electricity
The initial stage in the distribution of power is to transfer the electricity from the power station to a distribution centre. Due to the large amount of power that is to be transferred, the cables required need to operate at extra high voltage (66-275,000 volts). The cheapest form of transfer of extra high voltage power is through the use of overhead lines, in which the air is the insulation. Therefore, in most case, power is transferred from the power station to a distribution centre (also called a substation) by bare wires supported by massive steel towers.
The power is then transferred from the substation to local suburbs. This is usually done at a lower voltage (11-33,000 volts), however this is still higher than normal usage, and is therefore transferred either by overhead lines or specially designed underground cables. The power is distributed from the substation to a transformer located either within a factory or close to houses in residential areas.
The transformer converts the electricity from its current high voltage to low voltage (600 – 1,000 volts) for use within the home, office or factory. The electricity is supplied to the buildings via insulated aerial bundled cables or underground cables.
Within the house, factory or office, insulated cables are used for power points and connection to electrical equipment. There may also be cables for communications and data which operate at even lower voltages