Wire-line communication facilities serving electric power stations often require special high-voltage protection against the effects of fault-produced ground potential rise or induction voltages, or both. Some of the communication services are used for control and protective relaying purposes which may be called upon to perform critical operations during periods of these faults. This constitutes a major problem in the design of the wireline communications system since power faults usually result in the introduction of interfering voltages and currents into the communication circuit just at the time when the latter is most urgently required to perform its function. It is important to note that special high-voltage protection for the purpose of personnel safety and plant protection may be required even when critical services are not involved. Effective protection of any wire-line communications circuit requires coordinated protection on all circuits.