This recommendation applies to coupling devices for power line carrier (PLC) systems which are connected between the coupling capacitor(s) and the carrier-frequency connection to the PLC terminal (or to a similar coupling device, directly or via additional equipment, in the case of retransmission). The coupling device, in conjunction with the coupling capacitor(s) ensures: a) the efficient transmission of carrier-frequency signals between the carrier-frequency connection and the power line; b) the safety of personnel and the protection of the low-voltage parts of the installation against the effects of the power-frequency voltage and transient overvoltages. This recommendation also applies to coupling devices used in conjunction with PLC systems which are required to operate over power cables.