Measurement of ground resistance is a mandatory requirement for the installation and operation of electrical appliances, provided for by the operating rules and fire safety instructions.
There are several different methods for performing earth resistance measurements, depending on several factors, such as the nature and conditions of measurement, the magnitude of the resistance to be measured, the relative accuracy and speed of measurements.
Measurement of ground resistance is carried out to examine its condition. The process of taking measurements is carried out in several stages:
- The visible part of the grounding is examined, namely: the ground loop is checked, the reliability of the connection of grounding devices to the electrical network. The joints of wires and grounding parts are carefully examined. Cracks in the welding seams of the joints and loosening of the fastening bolts are not allowed, and the compliance of the inspected grounding with the installation rules is checked.
- Preparatory work for the measurement is in progress. These include the creation of an artificial current circuit, for which an auxiliary ground electrode is installed at least 40 meters from the grounding device, connected by a wire to the measuring device. The second electrode, called potential, is installed similarly to the auxiliary one at least 20 meters away, and is also connected to the measuring device with a wire.
- The final step is to measure the resistance of the grounding devices, for which the wire is connected to the measuring device and the ground electrode, and after that the resistance of the loop is directly measured.
Ground resistance is measured using special instruments that use the principle of potential drop created by alternating current between electrodes, one of which is called potential, the second - auxiliary. Based on the results of the measurements of the grounding device, a protocol is drawn up, on the basis of which a conclusion is made about its serviceability and the admission of the electrical installation to operation.
It has been observed that only in dry weather with minimal air humidity, soils have the highest resistivity values, and that is why it is recommended to use such weather conditions when planning a ground resistance measurement. Of course, such work is carried out in any weather and at different times of the year, for which there are standard seasonal coefficients that take into account the weather factor in the calculations.resistance. If we talk about the timing of their implementation, then annual checks of the grounding resistance of electrical installations are provided, and after repair work or reconstruction of the grounding.
These works involve specialists who have undergone special training, who know how to check the grounding and have the appropriate electrical safety approval.
