Conductor is a current carrying element made up of Aluminium or Copper with a specific cross section for the assigned rating, having resistance / km within certain specified limits.
Electrical Insulation (dielectric)
Insulation is provided over the conductors to electrically isolate them from one another. Various types of insulating materials used are : PVC, XLPE (Cross Linked Polyethylene), Rubber, etc.
An insulated conductor is termed as Core. A cable may have one or more cores. In a multiple core cable , the cores are helically stranded together. In twin, three & multi-core cables, the cores are laid up together with a suitable lay; the outer most layer has right-hand lay and the successive layers are laid with opposite lay direction.
Inner sheath (bedding)
Cables with stranded cores are provided with Inner Sheath applied either by extrusion or by wrapping. It is ensured that the shape is as circular as possible. Inner Sheath is so applied that it fits closely on the laid up cores & it should be possible to remove it without damage to the insulation. Thickness of Inner Sheath is specified in relevant standard and is based on calculated diameter over laid-up cores.
A wire, strip or a tape applied helically over the cable, to protect the cable from penetration by sharp objects, crushing forces, and damage from rodents or boring insects, is termed as Armour.
Armour is applied over the insulation in case of single core cables & over inner sheath in case of twin, three & multi core cables.
Outer sheath /Jacket is usually an extruded plastic cover over the laid-up or armoured core. PVC is a common sheathing material. Outer sheath provides mechanical, thermal, chemical and environmental protection. No electrical function is assigned to Outer sheath. The colour of outer sheath is normally black.