What is the second type of test, besides the clamp-on test, for measuring ground rod resistance?

The fall of potential test is recognized as a standard method for measuring the resistance of grounding electrodes, such as ground rods. This test works by introducing a known voltage into the grounding system while measuring the voltage drop across the ground rod. By using this method, it provides an effective way to assess the quality of the grounding system and its resistance to electrical currents.

In this test, electrodes are positioned at specified distances from the grounding rod and measurements are taken to calculate resistance based on voltage drop. It is particularly useful for determining how well the grounding rod is dissipating electricity into the earth, which is essential for safety in electrical installations.

The other techniques listed serve different purposes: the voltage drop test typically assesses load conditions rather than ground resistance; the insulation resistance test checks the integrity of insulation on conductors; and the continuity test ensures that an electrical path is complete without assessing resistance. Thus, these methods do not apply in the context of accurately measuring ground rod resistance like the fall of potential test does.