The grounding resistance measurement methods generally have the following methods: two-wire method, three-wire method, four-wire method, single-clamp method, and double-clamp method. Each has its own characteristics. When actually measuring, try to choose the correct way to make the measurement results accurate.
(Take the 8986 and 9066 grounding tester of BEHA in Germany as an example)
Two-line method
Condition: There must be a ground that is known to be well grounded, such as PEN, etc. The measured result is the measured ground and the known resistance. If it is known to be much smaller than the resistance of the ground, the measurement can be used as a result of the measured ground.
Applicable to: areas where the building is dense or cemented, etc., which cannot seal the pile.
Wiring: E+ES is connected to the ground and H+S is connected to the known ground.
2. Three-line method
Condition: There must be two ground rods: an auxiliary ground and a probe electrode.
The distance between each ground electrode is not less than 20 meters.
The principle is to apply current between the auxiliary ground and the measured ground.
The voltage drop between the ground and the probe electrode is measured. The measurement results include measuring the resistance of the cable itself.
Suitable for: grounding of foundations, grounding of construction sites and lightning protection.
Wiring: S is connected to the detector electrode, H is connected to the auxiliary ground, and E and ES are connected to the ground. .
3. Four-wire method
Basically, the same three-wire method replaces the three-wire method when measuring low-ground resistance and eliminating the influence of measuring cable resistance on the measurement result. When measuring, E and ES must be directly connected to the measured ground. This method is the most accurate of all grounding resistance measurement methods.
4. Single clamp measurement
Measure the grounding resistance of each grounding point in the multi-point grounding, and do not disconnect the grounding connection to prevent danger.
Applicable to: multi-point grounding, can not disconnect, measure the resistance of each grounding point.
Wiring: Use current clamps to monitor the current at the ground point being tested.
5. Double clamp method
Condition: Multi-point grounding, no auxiliary grounding pile, measuring a single grounding.
Wiring: Use the current clamp specified by the manufacturer to connect to the corresponding socket, and clamp the two clamps on the grounding conductor. The distance between the two clamps is greater than 0.25 m.
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