The Design of Submersible Electrode of a Branching Unit for an Optical Submarine Cable System

In optical fiber submarine cables, it has been planned to branch the cables through a branching unit. For the purpose of power feeding for the repeaters in the branched cable, a sea earth is arranged near the branching unit. The electrical potential field around the branching unit depends upon the distance between the sea earth and the branching unit. If the electrical potential gradient around the branching unit exceeds some level, there seems to be afraid of stray current that corrodes the branching unit housing (housing). In this paper, we describe the analytical electrical potential field around the branching unit and then show the designing guideline of the safety distance between the housing and the sea earth, that assures the non stray current corrosion of the branching unit for the life time of 25 years. In addition to analytical study, the results of sea experiments of the stray current corrosion are presented.