Abstract: In a shielded power cable of the type comprising inner and outer conductors separated by cable insulation defining a displacement current path between the conductors for high frequency currents, the cable insulation incorporates one or more coaxial layers of semiconductive material consisting of cable insulation material loaded with a conductive filler, such as carbon fibres or spheres. The semiconductive layer is designed to maximize high frequency losses thereby to facilitate attenuation of high voltage surges caused by lightning or by switching.