In which scenario does the clamp-on resistance test for ground rods work best?

The clamp-on resistance test is designed to effectively measure the resistance of a grounding electrode, such as a ground rod, independent of other connections or interference from parallel paths. When applied to an unconnected, single ground rod, the test determines the resistance of that specific rod without any effects from other connected systems or ground rods that might alter the readings.

In this scenario, since the ground rod is disconnected, there is no parallel resistance or additional grounding paths influencing the measurement. This makes it ideal for obtaining a clear, accurate reading of the rod's resistance, allowing for effective assessment of its grounding performance.

In contrast, when ground rods are connected, the test might measure the combined resistance of multiple rods or connections, which could lead to inaccurately low readings. Furthermore, utilizing the test on rods buried in concrete presents challenges in accurately measuring resistance due to potential isolation from moisture and soil conductivity, factors crucial for grounding efficiency.