EM-4055 earth resistance tester is a digital tester that allows to measure the earth resistance and ground resistivity (using Wenner´s method), as well as to detect parasitic voltages present in the ground. This earth resistance tester is suitable to measure earth systems in power substations, industries, distribution networks, etc., according to IEC 61557-5. Earth resistance tester is also suitable for soil resistivity measurements, in order to optimize the earth systems project. This tester is a fully automatic and easy-to-operate equipment. Before starting each measurement, the equipment will check that conditions are within appropriate limits and will notify the operator in case any abnormality turns up (too high interference voltage, too much resistance in test spikes, very low test current, etc). Then, the earth resistance tester will look for the most suitable range and show measurement results in an alphanumeric display. In order to conveniently test the earth system, EM-4055 allows to perform measurements using the test current which frequency may be operator-selected (270 Hz or 1470 Hz). On one hand, the lowest frequency will allow to analyze the earth system behavior related to fault currents of industrial frequency, while on the other hand, the measurement performed with the highest frequency will best show the behavior in connection with electrical currents caused by lightning and will offer a very high immunity related to interference voltages that are usually present in soils, specially near substations.