Why soil conditions dominate

Soil resistivity varies from a few ohm-metres in wet clay to several hundred in sand and rock. The same electrode design that easily meets its target on one site can miss it by a wide margin a few kilometres away. Earthing design has to start from a measurement, not a template.

Materials commonly used

Copper-bonded steel rods for general use

Chemical or maintenance-free electrodes where a low resistance must be held for years

Backfill and ground-enhancing compounds in high-resistivity or seasonally dry ground

Copper conductors and exothermic or mechanical joints for the connections

Bonding conductors for metallic services and structural steel

Seasonal behaviour

In Bangladesh the water table and soil moisture swing significantly between the monsoon and the dry season. An electrode measured in the monsoon can fail its target in April. Design for the dry-season condition, or use materials and geometry that hold resistance through the year.

Records

Earth resistance readings, taken after installation and repeated periodically, are the only evidence that the system still meets its target.