Some grounding resistance measuring instruments require disconnection for measurement, while others do not, mainly due to the following considerations. If they are not disconnected, the following situations will occur:

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1. If the grounding resistance of the electrode under test is very large or the wire is broken underground, the current source or generator in the measuring instrument will be open, and then the open circuit voltage will be conducted to the casing of the internal instrument and equipment through the internal grounding system. The open-circuit voltage of the hand-cranked generator is generally above 100V, and the open-circuit voltage of the battery-powered current source is generally below 50V.
2. If the internal electrical equipment leaks current, the current will be injected from the tested electrode to the ground, and a voltage drop will be generated on the surrounding ground, which is called ground voltage. If the ground voltage is small, it will affect the measurement result, and if the ground voltage is large, it will threaten the safety of personnel or damage the grounding resistance. surface.
3. Some non-standard grounding methods connect the two originally independent grounding systems through the casing of the instrument and equipment. The resistance value measured by the grounding resistance meter is not a single grounding resistance, but the parallel connection of the two system grounding resistances. Even if the ground electrode under test is broken, it cannot be detected.
It is better to disconnect the ground wire when measuring the ground resistance. If not, pay attention to avoid the above situation, and do:
(1) Measure the ground voltage first. If the ground voltage of points E and C is greater than the requirements of the measuring instrument, turn off the relevant electrical equipment, and turn off the power if necessary.
(2) Check and confirm that the electrode under test is well grounded, check the connection of the two independent grounding systems, and exclude irregular grounding points. Nowadays, the grounding system is generally required to share the ground electrode, so there are no two independent ground electrodes, and the external connection situation is not considered. To check for broken wires, measure the loop resistance.