Interconnected systems have increased considerably in recent years, and the large possible earth-fault currents resulting require further thought being given to earth system design, especially in areas of high soil resistivity. The paper discusses the special practical problems of the design, construction and testing of earth electrode systems for stations with possible earth-fault currents in excess of 3 kA. The basic components are reviewed, and principles of design are suggested for power station and large substation earthing installations. Several examples are considered in detail and brief notes are given of a number of other stations. The measurement of the dissipation resistance of large earth electrodes is discussed, and new techniques of resistance measurement which have been specially developed for use with large installations are described.