High voltage transmission lines are also used for transmitting carrier signals between 30 kHz and 500 kHz for remote control, voice communication, remote metering and protection and other applications, and are often referred to as PLC systems.

Line traps prevent transmission of these high-frequency signals to unwanted directions without loss of energy at power frequency. Line traps are series-connected to the transmission lines and are designed to withstand the rated power frequency current and the short circuit current to which the lines are subjected. OSD and MCD technology are available.