Wenner 4-Point Soil Resistivity Testing: A Field Guide
A practical guide to conducting Wenner 4-point soil resistivity measurements in the field, including equipment setup, measurement procedures, and common sources of error.
Soil resistivity is the single most important parameter in grounding system design. It determines the resistance of the grounding system to remote earth, the distribution of fault current in the soil, and the magnitude of step and touch voltages at the surface.
The Wenner 4-point method is the most widely used technique for measuring soil resistivity. The measurement procedure involves driving four equally spaced electrodes into the soil in a straight line. A known current is injected between the two outer electrodes, and the resulting voltage is measured between the two inner electrodes.