What is the difference between a traditional grounding resistance meter and a clamp-on grounding resistance meter

The measurement of grounding resistance testers is becoming more widespread and important. At present, there are two main methods for measuring grounding resistance: the traditional grounding resistance meter and the new clamp-on grounding resistance meter. The application of the two ground resistance measurement methods is analyzed below.

1. Operation method:

The grounding resistance meter must trip the grounding wire and hit the auxiliary grounding pin. The ground electrode to be measured is to be separated from the grounding system, and the voltage electrode and current electrode must be driven into the soil at a specified distance as an auxiliary electrode for measurement. The operation is more complicated and laborious.

The clamp-type grounding resistance meter is a non-contact measurement. You only need to clamp the jaw of the clamp meter to the ground wire to be tested, and the ground resistance value can be read from the LCD screen of the clamp meter. The operation is very simple.

2. Accuracy of measurement:

The accuracy of the grounding resistance meter depends on the position between the auxiliary electrodes and the relative position between them and the grounding electrode. If the position of the auxiliary electrode is restricted and cannot meet the calculated value, it will cause the so-called distribution error. For the same ground electrode, different auxiliary electrode positions may cause the measurement results to have a certain degree of dispersion. And this dispersion will reduce the credibility of the measurement results.

The Clamp-on Earth Resistance Tester does not need auxiliary electrodes, and there is no error in the arrangement of the poles. When repeated tests, the results have good consistency.

3. Test environment:

The grounding resistance meter adopts the voltage-current method, and two auxiliary grounding electrodes with relative position requirements must be inserted. Therefore, there must be soil that meets the position requirements near the test point.

The clamp ground resistance tester measures the loop resistance value, so the ground electrode to be tested must form a loop, and it cannot be directly measured for single-point grounding.

4. Other applications of clamp ground resistance tester:

In many environments (such as computer rooms in basements or floors, lightning rods, elevators, gas stations, grounding bodies covered by concrete, and grounding bodies that cannot be separated from the system, etc.), use traditional grounding resistance meters to measure grounding resistance is very difficult. Although they are also single-point grounding, if there is a grounding body clamp meter available on site, their grounding resistance can be measured, and there is no need to disconnect the grounding electrode from the system during the test (see the instruction manual). The Fluke Clamp Ground Resistance Tester can measure ground faults that cannot be measured by traditional methods. For example, in a grounding system, the grounding resistance value of their grounding electrode is qualified, but the connecting wire between the grounding electrode and the lightning protection belt or the grounding overhead line may be used for a long time, and the contact resistance may be too large or even open. The grounding resistance of the pole is qualified, but the grounding system is unqualified.

5. For the same ground electrode, when the measurement results of the two instruments are quite different, please pay attention to the following issues:

1) When testing with a traditional grounding resistance meter, whether the ground down conductor is tripped (that is, whether the tested ground electrode is separated from the grounding system). If it is not tripped, the resistance value measured by the shaker is the parallel value of all grounding resistances of the grounding system. This parallel value is much smaller than the grounding resistance of the grounding electrode, and it is meaningless.

2) The national standard GL/T621-1997 "Grounding of AC Electrical Devices" stipulates: "The sum of the ground resistance of the grounding electrode or natural grounding electrode and the resistance of the grounding wire is called the grounding resistance of the grounding device." Generally, traditional grounding The resistance meter can only measure the resistance of the ground electrode to the ground, but cannot measure the resistance of the ground wire. The ground resistance measured by the clamp meter is the sum of the ground resistance of the ground electrode and the ground wire resistance, which fully meets the requirements of the national standard.

3) If the grounding system has only a few grounding electrodes, there will be some errors in the measurement with a clamp meter, which are generally larger. If you want to get an accurate grounding resistance value, you can use the "Solution Program for Finite Point Grounding System" to solve it.

In summary, the two measuring methods of universal grounding resistance are conditionally restricted, and each has advantages and disadvantages that cannot be replaced by each other. The user should determine the measurement method according to the system structure and environment of the ground electrode to be tested in order to obtain credible measurement results.