PVC has been used as cable insulation for over 50 years, and is still used today. These examples are old, as they do not contain an earth conductor.
Although probably still servicable, the lack of an earth conductor means that only double insulated or Class II light fittings and switches can be used.
As many light fittings today require an earth connection, this type of cable is no longer used and should be replaced.
Shown here is a grey outer sheath with stranded copper cores, grey outer with solid tinned copper cores and white outer with tinned copper cores. There is no difference between the white and grey versions other than the colour.
As with the two core examples, only plastic insulated switches can be used with this type of wiring.
This cable was manufactured with red, white and blue cores for a short period.