Behaviour of m.v. power-distribution cables when subjected to external damage

Two series of tests have been carried out to compare conventional 4-core paper-insulated lead-sheathed cables with newer cables having combined neutral and earth (c.n.e.), some designs of which have synthetic insulation. In the first tests, resistance to mechanical damage was assessed, and although, in general, the c.n.e. cables are shown to be less robust, the use of synthetic insulation gives somewhat better resistance when the cable is struck by blunt objects. Service experience has also shown that most damage is now caused by mechanical plant, and the impact involved is such that faults will be produced in any of the cable designs. In the second series of tests, indentors were dropped onto live cables, a range of fault levels being used. Cables with synthetic insulation produced less flash, but provided a greater chance of spiking-type tools remaining live.