Medium voltage power lines - and sometimes also high voltage power lines - are not equipped with an earth wire. Consequently, replacement by an OPGW is not applicable in these cases. However, to equip such a transmission line with optical fibers, an OPtical Phase Conductor (OPPC) may be used. The optical cable has -like the OPGW -to serve two different functions. It must carry the permanent electrical current and it has to house and protect the optical fibers. Generally, the design of OPPCs follows the same rules as for the OPGW, yet taking into account the specific requirements arising from the electrical properties of the phase conductor to be substituted. Like the OPGW the OPPC has the advantage of no additional load for the towers.
Since in case of the OPPC the optical fibers are installed on high voltage level, the splicing technology is different from that for OPGW. Connections in the line must be carried out in a way that the cable as well as the joint box do not directly touch ground potential. A joint box can either be installed freely hanging between the insulator strings at strong poles or it must be placed on an insulator itself. At both ends of the lines electrical current and optical fibers must be separated. This can be done by special separators consisting of a splice closure placed on top or bottom of an insulator.
