An insulator for installation in an HV switching plant has a body (4) of hardened resin and at least one moulded metal armature 91) subject to high voltage and at least one electrode (10) cast into the body with connecting parts (12). The electrode(s) is/are made of a cast material containing at least one coarse and at least one fine electrically conducting filling agent. For the former, nickel flakes or small balls are used and for the latter, powdered rust is used. The nickel flakes or balls have a size between two and a hundred microns, the majority being about thirty microns in size. The rust particles have a size of 5 nanometres up to one micron.
