The TL-5 earth resistance meter is a digital instrument controlled by a microprocessor. It has been designed to take earth resistance and resistivity measurements, with the use of the Wenner method. The TL-5 unit is fully automatic and easy to use. Before taking a reading, the unit controls the installation's conditions to check that they are within the adequate limits, notifying the user of any abnormal situation (very high interference voltages, very low intensity of the test current, etc.). The TL-5 can be used to select two frequencies to generate the test current (270 Hz or 1470 Hz), in order to optimise the earthing test. The instrument has 4 ranges to measure resistances, covering the range that goes from 0.01 Ω to 20 kΩ. This instrument has been specially designed to monitor earthing systems in substations, industries, energy distribution grids, etc. in accordance with IEC 61557-5. It is also very useful to measure the specific earth resistivity, with the purpose of optimising the earthing system projects.