ITU-T Recommendations

In the case of earth faults in high or medium voltage AC networks, significant earth potential rise (EPR) can occur in the earthing structure where the current is discharged to the earth; typically this is in the earthing grid of the substation involved in the fault. When the earthing grid is connected metallically to long conductors such as earth wires, neutral conductors, counterpoises, cable sheaths, pipes and rails, the EPR can be transferred over far distances well beyond the zone of influence. Recommendation ITU-T K.104 describes the mechanism of potential transfer to a customer's premise with a special view of the transfer through the neutral conductor of a low-voltage network and the sheath of a telecommunication cable. Calculation techniques are given for the determination of the magnitude of EPR and transferred potential. Mitigation techniques for preventing the transfer of EPR are proposed. Different isolation techniques are proposed as possible mitigation techniques applicable in a telecommunication plant.