A Wenner four-pin soil resistivity survey involves five main steps: site preparation, equipment setup, measurement collection, data recording, and quality verification.
Site preparation: Identify two or more orthogonal traverse lines across the site. Each traverse must be unobstructed and at least three times the maximum A-spacing in length. Mark probe positions at each spacing interval.
Equipment setup: Connect the earth resistance tester to four probe leads. Drive the outer current probes (C1, C2) and inner potential probes (P1, P2) at equal spacing A. Probes should be driven 6 to 12 inches into undisturbed soil.
Measurement collection: Inject AC test current between C1 and C2 and measure the voltage across P1 and P2. Record the resistance reading R from the instrument. Calculate apparent resistivity as ρ = 2πAR. Repeat at each A-spacing from the minimum (typically 2 ft) to the maximum (typically 3x the grounding system diagonal).
Quality verification: Perform dual-current verification at each spacing. Readings that differ by more than 5% indicate interference from buried metallic structures or stray currents and must be investigated.
E&S Grounding Solutions provides full-service soil resistivity testing. Contact us at +1-310-318-7151 or info@esgrounding.com.