Why should HT cables have problems if they are properly sized and the joints are properly done? Overheating would occur if the cable is not sized according to load requirements-just like any other cable. Further I have witnessed the installation of 18 joints on a 36 kV cable-real surgical work by a Swiss Vendor-really professional-back breaking work done very clean. By the way it was done and the materials used-the joint seems to be stronger than the cable!!