The electrical insulator includes a laminated tube serving as a support for a covering of elastomer material constituting a plurality of annular fins which project from the tube. Two circular grooves and a helical groove are formed in the outside wall of the tube for receiving the optical waveguide. The circular grooves are parts of bearing surfaces which are formed at the ends of the tube and to which end fittings of the insulator are secured. The optical waveguide is embedded in the elastomer material and at the bottoms of the grooves.