a. During the test with the double clamp method, an effective closed loop must be established. The solution is to find an auxiliary grounding electrode, connect the grounding body under test with a well-grounded auxiliary ground (such as a water pipe) using a connecting wire, and clamp the two clamps onto the connecting wire (as shown in the figure): with a distance of about 30cm between them, press the "Double Clamp" key to enter the double clamp measurement interface, then press the "Test" key to directly display the measurement result. Different testing methods can be adopted according to different situations when measuring the grounding resistance of an independent grounding body.
b. When the computer room is on a low floor (first or second floor), the ground stake testing method can be used to directly measure the grounding resistance.
c. When the computer room is on a higher floor (above the second floor), the "independent grounding body" testing method can be used. This method is based on the theoretical assumption that the grounding resistance of the water pipe network is zero ohms, but in reality it has a resistance value. The test is divided into two steps: first, measure RA using the "independent grounding body" testing method; second, separately measure RB on the first floor using the "ground stake" testing method for the grounding resistance of the water pipe (at this time, the water pipe is regarded as an independent grounding body). (RA - RB) is the actual grounding resistance of the computer room grounding device.
d. When measuring resistance with the double clamp method, if the measured value shows overflow, it indicates that the resistance under test exceeds the measurement range of this instrument, or that the clamps are not clamped around any metal conductor or the grounding wire under test.
