Electrical cable. Cutaway end of a three-core and earth electrical cable. This cable has three insulated solid copper conductors and a bare solid copper earth wire. This type of cable is used in lighting circuits where a light can be turned on or off at either of two switches. These cabling colours (red is L1, yellow is L2, and blue is L3) were used in the UK up until April 2004, when they were changed to harmonise them with the rest of Europe. For the new colours, see T194/697.