Which instrument is used for the ground resistance test described?

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Measuring earth ground resistance requires delivering a controlled current into the soil through a separate electrode and sensing the resulting voltage to compute resistance. A 3-terminal Earth Ground Resistance Tester is built for this purpose, with separate current and potential leads that allow placing test probes at known distances from the grounding electrode and calculating the soil resistance accurately, usually using the fall‑of‑potential method. This setup minimizes errors from contact impedance and stray currents, giving a reliable reading of the grounding system’s resistance.

Digital ohmmeters and multimeters measure resistance between two points in a conductor and don’t inject current into the soil or account for the geometry of ground probes, so they’re not suitable for earth resistance tests. An insulation tester checks insulation resistance between conductors and earth at high voltage, not the resistance of the earth itself.