Cable construction Outer sheathing

Cables can be considered to be constructed in three parts the conductor, which must be of a suitable cross-section to carry the load current the insulation, which has a colour or number code for identification and the outer sheath, which may contain some means of providing protection from mechanical damage. 

In the past, there were fewer accidents because buried cables were better protected. Most of the supply authorities used paper-insulated, lead-sheathed, single-wire or steel-tape armoured and served cables and very often protected them with cable tiles. For economic reasons cable tiles are seldom used now and many of the mains laid in recent years are unarmoured CNE cables with plastic insulation and sheathing, such as PVC and cross-linked polyethylene (XLPE). The outer concentric conductor, which is the earthed neutral, is copper or aluminium tape and consequently more vulnerable to damage than a steel-wire-armoured cable. Every year more new mains cables of this type are laid so the resultant hazard to excavators is growing and more accidents can be expected to occur unless the construction industry becomes more effective at taking precautions against striking buried cables. 

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