Flex, like many other things, can become frayed and worn with continual use. Accidental damage can also occur to the sheath, which may dangerously expose the live cores. If this happens, a temporary repair can be easily made by wrapping a length of insulating tape around the flex, although new flex will need to be fitted as soon as possible.
Firstly, the correct type of flex for the job will have to be selected. In the case of a standard or table lamp, the commonest type in use is round PVC-sheathed flex, which has three cores where the lamp has metal parts or two cores if it is entirely made of plastic. Except in the case of unusually powerful fittings, 0.5 mm square size is adequate, and 0.7 mm should be used for lamps containing high-wattage bulbs. Enough flex should be bought to allow the nearest wall socket to be easily reached without causing any danger.
The first step in fitting new flex is to unplug the fitting or appliance, and the cover should always be screwed firmly back in place when the work has been completed and before plugging back in the fitting or appliance.