Causes and Handling Methods of Inaccurate Ground Resistance Testing in Lightning Protection Detection
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In lightning protection detection, there are many factors that cause inaccurate ground resistance readings. Generally, the reasons can be summarized as follows.
1. When testing high-rise buildings, using excessively long or thick wires increases wire resistance and induced voltage, causing measurement errors. In this case, wires with lower resistance should be used to minimize measurement errors.
2. The depth of the iron probe insertion should be greater than 1/4 of its length; otherwise, test errors will occur. Therefore, during testing, the iron probe should be driven as deep as possible.
3. When the tested grounding electrode is in a "common ground" situation, poor insulation or short circuits in equipment can cause a certain ground voltage on the grounding device, leading to unstable readings during measurement. In this case, power should be cut off for testing, or testing should be done at a place with a disconnecting card to avoid the influence of ground voltage.
4. Poor contact. If the tested object is rusty or the test wire is broken, intermittent connection or high resistance may be observed during testing. In this case, rust should be removed first; if the problem persists, use the resistance range of a multimeter to check the continuity of the test wire.
5. Since the ground resistance tester emits and receives current through iron probes to test the ground resistance of the grounding body, if the distance between the two probes and between the probes and the grounding body is too close, mutual interference will occur, causing errors. Therefore, during measurement, the grounding body, voltage probe, and current probe should be arranged in a straight line, with each pair 20 meters apart.
6. When the testing site has materials such as fill soil or gravel, measurement errors may occur due to different soil resistivity between the upper and lower layers. In this case, the iron probe should be driven deeper to make full contact with the soil beneath the fill layer or to avoid the fill layer, thereby reducing measurement errors.
7. When the tested grounding device and metal pipes or other metal objects are buried in a complex manner, the current direction of the measuring instrument's electrodes may be altered, causing poor or unstable measurement. In this case, the layout of the grounding body and metal pipes should be understood first, and a location with relatively less influence should be chosen for measurement.
8. Inaccurate measurement may be caused by potential differences on the ground surface or strong magnetic fields. In this case, try to stay away from areas with large potential differences or strong magnetic fields; if unavoidable, shorten the test wires relatively to reduce measurement errors.
9. Operator errors, such as not following the instruction manual, not repairing faulty instruments in a timely manner, using inaccurate instruments, or long-term lack of calibration, can also cause measurement errors.
Note: The above information and technical parameters are compiled and published by Yangzhou Darui Electrical Co., Ltd.
