Twin and earth is a name for a type of mains electricity cable. It comprises two sheathed current carrying conductors and an unsheathed protective conductor. Line and neutral are individually insulated, the earth conductor is bare.
There is an overall sheath of grey PVC (BS 6004), or white for low smoke compound (BS 7211)
This cable has long been used for unprotected outdoor use, but is no longer considered suitable because the outer sheath materials are prone to eventual degadation by ultraviolet. A coating of dark paint has sometimes been used to avoid the possibility of deterioration.
4mm², 6mm², 10mm², 16mm² and higher have stranded conductors