Is it true that the clamp-on resistance test for ground rods works best on connected ground rods?

The clamp-on resistance test for ground rods is designed to measure the resistance of grounding systems without the need to disconnect them from the system. This method is particularly effective when ground rods are isolated, allowing for accurate resistance measurements without interference from parallel paths or other grounding elements.

When ground rods are connected, the presence of additional resistive paths can significantly affect the accuracy of the resistance measurement, potentially leading to under- or overestimation of the actual resistance of the ground rod. The test relies on the principle of measuring the voltage drop across a known current injected into the ground system; if other grounding elements are in play, they can alter the distribution of current and thereby distort the results.

Thus, the effectiveness of the clamp-on resistance test is compromised when ground rods are connected, making the statement false. It is important to perform this test on individual ground rods or to have well-defined conditions to ensure the accuracy of the readings.