In order to achieve an effective lightning protection system, soil resistivity is a crucial factor when considering any electrical grounding design – it describes the degree to which the soil will resist the flow of electricity and must always be taken into account when designing systems reliant on the current passing through the surface of the earth.
Testing is a vital part of the system installation, as soil quality varies from place to place. Factors affecting the soil resistivity include temperature, moisture and chemical content. The geology of the particular area also plays a part, as significantly different soil conditions may exist only a short distance away from each other.
The process of soil resistivity testing comprises measuring an amount of soil to ascertain its conductivity, using the relevant equipment. To provide maximum protection, the resulting data is recorded and used as a basis to create the most appropriate system.
From simple electrical designs, to dedicated low-resistance grounding systems, including the more complex ground potential rise issues, the importance of soil resistivity testing is the same when creating every kind of lightning protection system. A good soil model is the basis of all grounding designs.
Our experienced team will carry out a detailed study to measure the ground’s capacity in relation to an electrical current, analysing our findings for new earthing systems. Electrical resistivity is expressed in ohm-metres. The test comprises placing probes into the soil to measure the resistivity.
Using computer software, the raw data is then processed to calculate the actual resistivity of the soil. The testing is carried out as close to the planned grounding system as possible. It is important that electrical interference doesn’t cause unwanted signal noise to enter the meter.
Care must also be taken to ensure no metallic objects are “short-cutting” the electrical path between the probes. This is achieved by ensuring the relevant distance is maintained between the pins and any buried metallic structures.
Once the soil resistivity measurements have been determined, the design of the new lightning protection system can begin. The earthing system plays a crucial role: it safely dissipates the lightning currents to the ground and is fundamental in the effective operation of the surge protection devices. Hence the importance of soil resistivity testing cannot be over-emphasised.