Abstract :
Section (1) sets out the means to be taken by way of external protection to ensure that mains cables entering a power or distribution station will not be destroyed by an oil fire of short duration or help the spread of an extraneous fire. The means favoured for new installations is the use of a moulded asbestos material which has in the best degree obtainable the thermal characteristics required. To meet the case where cables are run without exterior metal protection, for positions having special fire risks and for such special uses as for switchboard connections, a new type of cable dielectric [described in Section (2)] has been developed which of itself possesses a high degree of fire resistance. The material is of a rubber-like nature, and the dimensions of the cable and the technique of installation are the same as for rubber-insulated cables. Section (3) describes a highly important series of tests made generally under conditions as nearly as possible simulating those obtaining in coal mines?an investigation made in close collaboration with H.M. Electrical Inspector of Mines. The experiments show that, in the great majority of cases, thecables withstand any transient flames such as would arise from an explosion of fire-damp, and generally that it is very difficult to set fire to a cable under conditions held fairly to simulate working conditions in a pit. In the case of trailing cables the tests have been carried through in some cases under conditions much more severe than can occur in practice. These tests have indicated that, to secure the maximum degree of safety from fire due to internal faults, a fire-resisting type of dielectric may be desirable, and that special provision may be necessary as regards both screening of the cable and the provision of earth-leakage protection. Section (4) is a note on the cold-pouring, cold-setting type of compound recently brought into prominence for emergency repairs which may have to be made under conditions both of urgen- cy and of atmosphere that would preclude the use of heaters of the flame type and also would not allow of the ordinary long time for cooling and topping-up on contraction. The main features of the compound are: (a) That certain ingredients mixed immediately before pouring cause the compound to set after a short period from the time of mixing; (b) that there is little or no contraction on setting; (c) that the electrical characteristics, although not so high as those of the best pitch compounds, are sufficiently good for service conditions; and (d) that the compound has proved to have ample stability for emergency joints under all conditions likely to be encountered.
