Maximum allowable working voltages in cables

IN recent years there has been a marked tendency, temporarily interrupted by the war, to operate electric power cable at increasingly higher voltages. For these higher voltage cables, the electric stress, or voltage per unit thickness of insulation is much higher than for the lower voltage cables, because the limiting overall dimensions have necessitated a reduction in the factor of safety, partly compensated for by improvement in the qualities of the insulating materials. When cables of still higher voltages are manufactured, the voltage stresses in the insulation will undoubtedly be proportionally higher again.