The Ground Resistance Tester Model 6418 measures ground rod, busbar, and grid resistance and impedance without the use of auxiliary rods. Clamp-on ground resistance testers can be used in multi-grounded systems without disconnecting or de-energizing the ground system under test. The Model 6418 simply clamps around the grounding electrode or conductor and measures the resistance to ground. By performing measurements on intact ground systems, the user also verifies the quality of the grounding connections and bonds. Resistance and continuity of grounding loops around pads and buildings may also be measured.