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Common methods of grounding resistance tester

time:2021/1/17   source:华天电力  reading:271 time

The measurement methods of the ground resistance tester are generally as follows: two-wire method, three-wire method, four-wire method, single clamp method and double clamp method. Each has its own characteristics. In actual measurement, try to choose the correct method to make the measurement results accurate.


1. Two-wire method

Condition: It is necessary to have a well-known 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 result.

Applicable to: areas where piles cannot be driven, such as dense buildings or concrete floors.

Wiring: E+ES is connected to the measured ground, H+S is connected to the known ground.


Earth Resistance Tester.png


2. Three-line method

Conditions: It is necessary to have two ground rods: an auxiliary ground and an exploration 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 exploration electrode. The measurement results include measuring the resistance of the cable itself.

Applicable to: grounding of foundation, construction site and lightning ball type lightning rod QPZ grounding.

Wiring: S is connected to the exploration electrode, H is connected to the auxiliary ground, and E and ES are connected to the measured ground.


3. 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 results. When measuring, E and ES must be directly connected to the measured ground separately. This method is the most accurate of all ground resistance measurement methods.


4. Single clamp measurement

Condition: Measure the ground resistance of each connection address in the multi-point grounding, and cannot disconnect the ground connection to prevent risks.

Applicable to: multi-point grounding, connection cannot be disconnected, resistance measurement of each connection address.

Wiring: Use a current clamp to monitor the current on the address being tested.


5. Double clamp method

Conditions: Multi-point grounding, no auxiliary ground stakes, measurement of 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 should be greater than 0.25 meters.

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