ITU-T Recommendations

Telecommunication systems are vulnerable to the earth potential rise (EPR) that can occur in power systems, and they are also vulnerable to the transfer of EPR outside the zone of influence (ZOI), which should also be considered. A quick estimate of the earth potential rise is obtained from the product (Ie × Re) of the current Ie flowing through an earth electrode and the resistance Re to earth of that earth electrode.

In this Recommendation methods of different complexity are given for measuring the resistance to earth of earth electrodes or even complex earthing systems. The described methods provide simple methods and more sophisticated measurements through the use of computer-based earthing multimeters. Guidance is given on the relevance of each of the different methods for different purposes.

Techniques are also given for the elimination of interference and disturbance voltages for earthing measurements.

In practice it may be necessary to determine or at least estimate the impedance to earth of a power system installation already in the design phase. For these purposes, techniques of calculating the resistance/impedance to earth of isolated, as well as interconnected, earthing systems are also included.