Just as you would expect, there is a multitude of cable types available. For domestic work, however, we need only concern ourselves with a few.
Single core cable is mostly used for industrial applications where it is run in conduits.
In domestic wiring, it is usually only used for certain situations. Here they consist of stranded conductors twisted together and housed in a PVC covering. 6 mm sq. single core, colour coded green and yellow, is used for supplementary earth bonding. 10mm sq (minimum) single core colour coded green and yellow is used for the main earth bonding conductors between the earth terminal block in the consumer unit and incoming metal water, gas and oil service pipes. 16 mm sq. single core colour coded green and yellow is used for connecting the earth terminal on the consumer unit to the Company’s earth connection. 16 mm sq. single core which is insulated and sheathed, colour coded brown (old cable colour = red) for live or blue (old cable colour = black) for neutral, is used for the connection of the consumer unit to the meter.
Two core and earth
Often referred to as ‘twin and earth’ these may have solid conductors or separate strands twisted together to provide flexibility for larger cables. The live and neutral are colour code insulated. The earth is not insulated. All three are then sheathed in a protective layer. Insulation must be provided for the earth conductor when it is exposed to make connections. This is done using green and yellow sleeving available from merchants.
Three core and earth
This is similar to two core but has three conductors, colour coded brown, grey and black (old cable colours = red, yellow, blue) as well as an earth. It is used where two way lighting is needed. It provides the necessary additional conductor between the two switches operating the same light fitting. These colours are for identification purposes only as any, or all may be live depending on how the circuit is wired