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 result accurate.
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 the 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: one auxiliary ground and one probe 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, and measure the voltage drop between the ground and the detecting electrode. The measurement results include measuring the resistance of the cable itself.
Applicable to: grounding of the foundation, grounding of the construction site and lightning protection ball lightning rod QPZ grounding.
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
Condition: 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.