A method of welding together cable insulations of cables having cores insulated by sheaths of polymeric insulation material capable of at least softening when heated, the method including electrically connecting the cores of the cables to be joined; heating the cable insulations by passing a current through the cores of the electrically connected cables effective to provide Joule heating sufficient to cause the cable insulations to at least soften; and pressing the heated cable insulations together with a pressure sufficient to cause the heated cable insulations to weld together.