Abstract: In the manufacture of a cable core comprising a moisture-impermeable multi-wire conductor, the conductor is stranded in a conventional manner and, after a fluid-impermeable layer of plastics material has been extruded over the conductor to form the core, the core is wound around the hub of a cable drum in such a way that each end of the wound core is exposed and accessible. One exposed end of the wound core is sealed and air is evacuated from the conductor interstices by a vacuum pump cemented to the other exposed end of the wound core. A source of semi-conductive moisture-impermeable compound in a liquid or semi-liquid state is then connected to the exposed end of the wound core and moisture-impermeable compound is drawn into and flows along the evacuated conductor interstices until the interstices are filled throughout the length of the core. The moisture-impermeable compound in the interstices is then permitted to solidify or thicken to such an extent that it will not readily flow from the conductor.