PVC

Cable insulated with PVC often has a thicker PVC sheath over the insulation and is then described as PVC insulated PVC sheathred cable or , simply , PVC/PVC . More than one insulated conductor can be embedded in the same sheath , so that one can have single , twin  , three , or four-core PVC/PVC cables , if one of the conductors is intended as a circuit protective conductor , it requires no insulation , although it must be sleeved at terminals and connections , up to a cross-sectional area of 6mm square , and may be enclosed directly in the sheath . Figure 2.6 showns a cable known as twin and earth PVC/PVC . It has two PVC insulated conductors and one unisulated conductor all embedded in the same PVC sheath .

Rubber
Butyl rubber and silicone rubber cables are usually sheathed with thick butyl and silicone rubber respectively .