Difficulties are experienced by telecommunication, protection, and relay engineers in determining the "appropriate" values of power station ground potential rise (GPR) or the longitudinally induced voltages (LI) into wire-line telecommunications facilities (or both) including their probability, waveform, and duration, which are to be used in developing the specifications for systems and component protection. Suitably rated protection devices are required for personnel safety and for the protection and continuity of service for wire-line facilities that either enter electric power stations or that are otherwise exposed to the influence of high-electric power circuits. (See ANSI/IEEE Std 487-1980 [51]) This standard provides guidance for the calculation of these interfering voltages and guidance for their appropriate reduction from worst-case values for use in wire-line telecommunication protection design. Information is also included for the determination of (1) The fault current and earth return current levels; their probability, waveform, and duration; and the impedance to remote earthing points used in these GPR and LI calculations as well as the effective X/R ratio. (2) The zone of influence of the power station GPR. (3) The calculation of the inducing currents, the mutual impedance between (4) The channel time requirements for wire-line telecommunication facilities power and wire-line telecommunication facilities, and shield factors. where noninterruptible channels are required for protective relaying, etc.