A line tension switch, by the nature of its application, must mechanically support the line and provide high voltage electrical insulation when the switch is in the open position. Almost since the inception of the electrical power industry, the most dependable means of providing these two basic functions has been the porcelain strain insulator. This classic design approach imposes basically compressive stresses in the porcelain shell when the unit is subjected to tensile loads. The conversion of tensile forces to compressive stress comes about through the provision of properly disposed angular surfaces. The metallic surfaces involved are coated with a thin, somewhat resilient coating which allows a slight amount of relative movement producing a wedging action, setting up compressive stress, as opposed to sheer or tensile stress in the porcelain. The porcelain itself has relatively very high compressive strength as opposed to the sheer and tensile strength characteristics.

Another aspect of this classic design is the fact that the mechanically stressed portion of the strain insulator is completely enclosed within a solid metal housing, which is the cap of the strain insulator. This metal cap provides substantial protection for this stressed portion of the insulator. The insulator units used in the Bridges Electric, Inc. line of line tension switches are assembled using high strength, chip resistant, alumina porcelain shells. The units are assembled in special precision jigs. The insulator incorporates the same materials, techniques, production proof tests, and quality control assurances that are used on standard strain insulators. The insulator units are assembled into switch assemblies by means of ¾-10 threaded connections. These joints are pinned with solid ¼” diameter stainless steel drive lock pins.