Discover professional instruments for measuring earth resistance and soil resistivity in this specialised electronic instrumentation category.
Earth testers or tellurometers: essential instruments for electrical safety
Earth resistance testers, also known as earth testers or tellurometers, are indispensable instruments for ensuring the safety and efficiency of electrical installations. These devices accurately measure earth resistance and soil resistivity, two key parameters that protect people and equipment against electric faults, leakage currents and lightning strikes. A proper earthing system provides a low-resistance path to safely dissipate fault currents into the ground. For this reason, owning a reliable soil resistivity meter is essential in residential, commercial, industrial and telecommunications environments.
Why it is important to measure earth resistance and soil resistivity
An effective earthing system ensures that electrical faults are safely diverted to the ground, preventing damage to installations and reducing the risk of electric shock. Using an earth tester allows engineers and electricians to verify compliance with safety standards such as BS 7671 (IET Wiring Regulations) and IEC 60364. The soil resistivity determines how easily the ground conducts electricity and is therefore crucial when designing new earthing systems. A soil resistivity meter provides the necessary data to determine the number, length and placement of ground rods to achieve an optimal resistance value.
Measurement methods using test spikes: 2, 3 and 4-point techniques
Earth resistance measuring instruments employ different test methods depending on the number of spikes or electrodes inserted into the ground. Each technique offers advantages based on the site conditions, level of accuracy required and the type of installation under test.
Two-point method
The simplest technique, the two-point method, uses the existing earthing system and one auxiliary test spike. The tester injects a current between these two points and measures the voltage drop. While less accurate, this quick-check method is suitable for routine maintenance or situations where it is not practical to install additional test spikes.
Three-point or fall-of-potential method
The three-point method, also known as the fall-of-potential test, is the most widely used and internationally recognised. It involves three spikes: one connected to the earth system under test, one for current injection and one for potential measurement. The earth resistance tester applies a current between the current electrode and the system under test, then measures the potential difference between the potential electrode and the earth. From these readings, the resistance value is calculated. This method provides high accuracy and is ideal for electrical installations, substations and lightning protection systems.
Four-point or Wenner method
The four-point (Wenner) method is primarily used to measure soil resistivity. Four equally spaced electrodes are driven into the ground in a straight line. The soil resistivity meter injects current through the two outer spikes and measures the voltage between the inner pair. The resistivity (ρ) is then calculated using the Wenner formula (ρ = 2πaR), where “a” is the spacing between electrodes and “R” the measured resistance. This method is essential for engineers designing complex earthing systems, allowing them to evaluate ground conditions before installation.
Clamp-on or spike-less method
Modern digital earth testers can perform measurements without test spikes, using a clamp to measure induced current on the earth conductor. This technique is extremely fast and does not require disconnecting the system. It is ideal for installations where multiple earthing systems are interconnected, such as office buildings or data centres. However, it is not suitable for isolated systems without a return path for current.
Applications of earth testers and soil resistivity meters
Earth resistance testers and soil resistivity meters are widely used across multiple sectors. In residential and commercial buildings, they verify that earthing systems comply with safety regulations. In industrial maintenance, they are used to check transformers, switchboards and heavy machinery. In telecommunications, proper earthing minimises interference and prevents equipment damage from static discharge. They are also critical in renewable energy installations such as wind farms and photovoltaic plants, ensuring reliable grounding of turbines and inverters. In addition, these instruments are frequently used by test laboratories, inspection bodies and electrical engineering firms.
Choosing the right tellurometer or earth resistance tester
When selecting a tellurometer or earth resistance tester, several factors must be considered: measurement range, accuracy, supported methods (2, 3 or 4-point testing), ease of use and robustness. Professional instruments include features such as backlit displays, internal memory, USB or Bluetooth connectivity, and software for data logging and reporting. The tester should be regularly calibrated and comply with international safety standards. A high-quality earth tester provides stable, repeatable results even in high-resistance soils or challenging environmental conditions.
Best practices for accurate and reliable measurements
For consistent and accurate readings, measurements should be taken under stable environmental conditions, preferably when the soil is slightly moist. Test spikes should be driven 30–50 cm into the ground, aligned in a straight line and spaced sufficiently apart, typically 5 to 10 metres. Repeating the measurement at slightly different positions helps verify consistency. It is also important to inspect test leads and connectors regularly and ensure that the instrument remains properly calibrated. Following these best practices ensures reliable data and helps detect early signs of deterioration in earthing systems.
Electrónica Embajadores: your specialist in measurement instrumentation
At Electrónica Embajadores, we offer an extensive selection of earth resistance testers, ground resistance meters and soil resistivity meters from leading international brands. Our catalogue includes portable, multifunctional and professional models, as well as accessories such as test spikes, cables and carrying cases. We provide expert technical advice to help you choose the most suitable instrument according to the type of soil, installation and applicable standards.
