The electrical resistance of a unit cube of soil, in ohm-cm. Low resistivity means plenty of dissolved salts and moisture, aggressive corrosion and easy current spread; values under about 1,000 ohm-cm are severely corrosive, while dry sand can top 50,000. It is measured with the Wenner four-pin method, where resistivity equals 2 x pi x pin spacing x measured resistance, or in a soil box, and it drives anode and groundbed design.
Soil resistivity is 25,000 ohm-cm up on the ridge, zinc won't throw enough current, we need mags there.
Run the Wenner test at several pin spacings. The spacing roughly equals the depth sampled, so it shows whether deeper soil is wetter and better for a groundbed.
Also heard as
- resistivity
- Wenner four-pin
- four-pin test
Related terms
Electrolyte
Conductive medium such as soil, seawater or concrete pore water that carries ionic current between anode and cathode.
Mag anode
Field name for a magnesium sacrificial anode, the high-voltage choice for high-resistivity soils.
Groundbed
Group of impressed-current anodes buried in backfill that discharges rectifier current into the earth.
Sacrificial anode
Block of a more active metal such as magnesium, zinc or aluminum that corrodes to protect connected steel.