Soil resistivity testing requires a calibrated earth resistance tester (also called a Wenner meter or four-terminal earth tester), four steel probes, and sufficient test lead wire to reach the maximum A-spacing.
Commonly used instruments include the AEMC 4620 (4-terminal, 4-wire), the Megger DET4TC2, and the Fluke 1625-2. All instruments must be NIST-traceable calibrated and rated for the test environment. For hazardous locations (Class I or Class II), intrinsically safe instruments are required.
Test leads must be long enough to reach the maximum A-spacing, which is typically three times the diagonal dimension of the grounding system. For a 500 ft x 500 ft substation, this requires leads of approximately 2,100 ft per traverse. Color-coded leads (C1, P1, P2, C2) prevent wiring errors.
Additional equipment includes: steel probes (3/8" diameter, 18" length), a probe driver, a measuring tape or laser distance meter, and a field data sheet. GPS coordinates should be recorded for each traverse endpoint.
E&S Grounding Solutions maintains a full complement of calibrated soil resistivity testing equipment. Contact us at +1-310-318-7151 or info@esgrounding.com.