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Common methods for testing ground resistance

time:2021/2/22   source:华天电力  reading:257 time

The grounding resistance tester is not only powerful, but also capable of coping with various complex situations on site, such as effectively eliminating interference, automatically tracking appropriate test conditions, and promptly prompting various problems, etc. It is an ideal instrument for testing the quality of grounding devices .


Common test methods of grounding resistance testers include: two-wire method, three-wire method, four-wire method, single clamp method and double clamp method. These five methods have their own characteristics. In actual measurement, try to choose the appropriate test method. In order to make the test results accurate.


One, two-wire method


Condition: There must be a known well grounded ground, such as PEN, etc. The measured result is the sum of the resistance of the measured ground and the known ground. If the known ground is much smaller than the resistance of the measured ground, the measurement result can be used as the measured ground result.


Applicable to: dense buildings or cement ground and other sealed areas that cannot be piled. Wiring: E+ES is connected to the measured ground, H+S is connected to the known ground.


Earth Resistance Tester.png


The second, three-wire method


Condition: There must be two ground rods: an auxiliary ground and a detection electrode. The distance between each ground electrode is not less than 20 meters. The principle is to add a current between the auxiliary ground and the measured ground to measure the voltage drop between the measured ground and the probe electrode. The measurement result includes the resistance of the cable itself.


Applicable to: foundation grounding, construction site grounding and lightning protection grounding. Wiring: S is connected to the detection electrode, H is connected to the auxiliary ground, and E and ES are connected to the ground to be measured.


The third, four-wire method


Basically the same as the three-wire method, it replaces the three-wire method when measuring low ground resistance and eliminating the influence of the measurement cable resistance on the measurement result. E and ES must be directly connected to the measured ground separately during measurement. This method has high accuracy among all ground resistance measurement methods.


Fourth, single clamp measurement


Measure the grounding resistance of each grounding point in the multi-point grounding, and can not disconnect the grounding connection to prevent danger.


Applicable to: multi-point grounding without disconnection, measuring the resistance of each grounding point. Wiring: Use a current clamp to monitor the current on the ground point under test.


Fifth, double clamp method


Conditions: Multi-point grounding, no auxiliary ground piles, and single grounding measurement. Wiring: Use the manufacturer's current clamp to connect to the corresponding socket, and clamp the two clamps on the grounding conductor. The distance between the two clamps should be greater than 0.25 meters.

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