Soil resistance is the reaction of the earth when it can pass an electric current. The grounding measurement should be made with precision using a ground resistance tester (Earth Meger). How to measure the grounding resistance? What are the factors affecting soil resistance?

Grounding Resistance (earth resistance) is the reaction of the ground when it can pass electric current. Earth is actually a weaker conductor than normal conductors such as copper. However, if the field is large enough for the current, the resistance will be low and earth can become a good conductor. For this reason, there is a resistance that must exist between the conductors and the ground in our system. Before the facility is established, these measurements are made, and after the necessary calculations and preparation, the installation is carried out.

Resistivity of Soil (Specific Resistivity) is the resistance of 1 m3 soil. Its value depends on the structure of the soil and the water content in it. The resistance of an electrode to earth depends on the resistivity of the soil. The insulation of each conductor against the earth is measured with a soil resistance tester (earth meger) and the insulation of the conductors against each other is measured with an "insulation tester" (insulation meger). In short, all insulation resistance measuring devices (megers) are specially produced portable ohmmeters.

Factors Affecting Soil Resistance

► Vegetative structures or other electrical installations can expand the size. Different grounding electrodes may be needed for such changes.

► Possible situations such as adding more sensitive modern computer-controlled equipment to facilities magnify electrical noise. Old equipment can cause this electrical noise due to incompatibility with these new equipment.

► Systems such as non-metallic pipes and ducts laid underground can threaten safety in terms of low ground resistance.

► One of the other important factors affecting soil resistance is the humidity of the soil.

Theoretical Principle of Grounding Measurement

The first theoretical measurement logic and calculations of measurements made with soil meger were provided by Dr. Frank Wenner did it in 1915. Classic type earth meggers have three electrodes: E, P, C. E: Earth Electrode C: Current Electrode P: Potential Electrode We, as the user, obtain the potential difference between E and P by applying constant current to the E and C electrodes. With the V/I calculation, the instrument gives us the ground resistance R.

How to Measure Grounding Resistance (Earth Resistance)?

The most common method is the measurement with 2 stakes (3 probes). The P and C electrodes are driven deeply into the ground. The distance between these electrodes should be 5-10 m. We connect the green wire to the grounding busbar. It is absolutely necessary to separate the busbar. We connect the yellow wire to the potential electrode (P), and the red wire to the current electrode (C). The moist soil on which the electrodes are driven makes our work easier. It enables the piles to be driven easily and the soil resistance to be lower. If the soil is dry, moistening can be achieved by pouring water.

How to Measure Soil Resistivity (Specific Resistivity)?

The lower the resistance of the ground itself, the lower the resistance of the grounding. The specific resistance can be measured with the help of 4 stakes using the Wenner method. The piles are driven at an equal distance and the measurement is performed.