1 Road Safety And Automobile Association Patrol In Great Britain

TRANSFERRING ELECTRICITY: ELECTRIC CABLES


When electricity has been generated it then has to be taken to the place where it will be used. A complete round circuit is needed. The circuit goes from the source, which might be a battery or a generator or a transformer, to the place of use and back to the source again. The electric current travels along a conductor.
The two most widely used materials for making conductors are the metals copper and aluminum.
The current must be kept traveling along its conductors, and must not escape, so a conductor is surrounded by insulation. The materials, which are most commonly used as insulation, are air, synthetic, rubber, and the plastics PVC (polyvinylchloride) and PE (polyethylene). An insulator is a substance, which is such a bad conductor, that it hardly allows any current to pass through it.
Where there is plenty of space, air can be used as insulation.
This is done in the electricity grid system. The power lines on the pylons are bare aluminum wires. At the pylons they are supported by glass or porcelain insulators, but along their lengths they are insulated from each other by the air between them.
Where a person might touch the conductor, or where the conductor might touch the ground or metalwork, air is not suitable insulation. In these cases some solid insulation, like PVC or PE, must be placed closely around each conductor.
If the insulation is to be exposed to the weather over a long period, or is to be buried in the ground, or is to be dragged over the ground or across concrete, then it will need extra protection. It will need an outer cover. This outer cover is a protection against water and against mechanical damage.
So in an electric cable there are three main parts: a metal conductor, insulation, and an outer cover. The metal conductor and its insulation are together known as the core of the cable. A cable may have one core, two cores, four cores, or many cores, all within the outer cover.
The conductor carries the current; the insulation keeps the current in the conductor; and the outer cover protects the insulation.
Topic # 12