Ground resistance tester

Data records

• In the fall-of-potential (three-pole) method the instrument passes current between the electrode under test and an outer auxiliary stake, senses the voltage between the electrode and an inner stake driven along the same line, and displays the electrode's resistance to ground from the two. Source: Fluke learn article, web page edition. Verified 2026-10-27. Record instr.ground-resistance-tester.fall-of-potential
• Moving the potential stake to several positions between the electrode and the current stake and plotting resistance against distance gives a curve with a plateau; the plateau value is the electrode's resistance, and a curve that departs from that shape shows that the measurement is disturbed. Source: Megger Electrical Tester article, 2007-11-01 edition. Verified 2026-10-27. Record instr.ground-resistance-tester.fall-of-potential-plateau
• A ground resistance tester drives a known alternating test current into the soil through the electrode under test, measures the potential difference that the current produces, and reports the quotient as a resistance reading. Source: Fluke learn article, web page edition. Verified 2026-10-27. Record instr.ground-resistance-tester.reads
• In the selective (attached rod) method a current clamp around the electrode under test measures only the instrument's own test current flowing in that electrode, so a fall-of-potential measurement is made without disconnecting the electrode from the parallel grounding system. Source: Megger Electrical Tester article, 2007-11-01 edition. Verified 2026-10-27. Record instr.ground-resistance-tester.selective-method
• Resistivity readings repeated at several stake spacings and along a second axis produce a profile of the soil that guides the design and placement of a grounding electrode system; resistivity changes with soil composition, moisture and temperature and so varies with the seasons. Source: Fluke learn article, web page edition. Verified 2026-10-27. Record instr.ground-resistance-tester.soil-resistivity-use
• For soil resistivity the four-pole Wenner arrangement places four stakes in a straight line at equal spacing; the instrument drives current through the outer pair, senses voltage between the inner pair, and the resistance reading is converted to resistivity using the stake spacing. Source: Fluke learn article, web page edition. Verified 2026-10-27. Record instr.ground-resistance-tester.soil-resistivity-wenner
• Four-terminal testers fitted with clamp inputs also perform the stakeless test, in which the test current is induced into the ground system through one clamp and the current flowing in the electrode under test is read through a second clamp, with no stake and no direct connection. Source: Megger product page, web page edition. Verified 2026-10-27. Record instr.ground-resistance-tester.stakeless-mode
• The test current is alternating, at a frequency chosen not to be an integer multiple of the power frequency so that noise currents flowing in the soil are rejected; some instruments offer several selectable test frequencies and others select the quietest frequency automatically. Source: Megger Electrical Tester article, 2007-11-01 edition. Verified 2026-10-27. Record instr.ground-resistance-tester.test-frequency
• A three-terminal instrument suffices for measuring the resistance of a ground electrode, while a four-terminal instrument adds soil resistivity measurement and the higher-resolution readings needed for the slope method and for resistivity surveys over large areas. Source: Megger product page, web page edition. Verified 2026-10-27. Record instr.ground-resistance-tester.variants