The fixed wiring in a house or flat supplying the various circuits is usually flat, twin-core and earth PVC sheathed with some sections of a lighting circuit such as 2-way switching being wired in flat 3-core and earth PVC sheathed cable. The sheath is either grey or white. Within the sheath of twin-core and earth cable are two PVC insulated, current-carrying, copper conductors: one red, one black and an uninsulated copper conductor positioned between them.
The red conductor is normally used as the live and the black as the neutral, but the return wire from a switch to the light of a lighting circuit although live when the switch is’ON’is a black wire which needs a red sleeve slipped over each end. The uninsulated wire is the earth conductor and its bare end within a switch or any other accessory must be enclosed in a green yellow PVC sleeve, so that it does not make contact with a current carrying terminal. Core colours of a 3-core and earth cable are red, yellow and blue, and when used in a switch circuit the,ends of the blue and yellow conductors must be enclosed in red sleeving. Sizes of cables used in home wiring are 1.0mm2, 1.5mm2, 2.5mm2, 4mm2, 6mm2 and 10mm2.