Earth Resistance Testing: Fall-of-Potential, Clamp-On and Which One to Trust
2 June 2026 · 6 min read
The three field methods used on Indian sites, when each is valid, and the mistakes that produce falsely low readings.
Fall-of-potential (3-pole / 4-pole)
The reference method in IS 3043. The electrode is disconnected at the test link, and current and potential spikes are driven along a straight line at 62% and 100% of a distance at least five times the electrode depth. A flat plateau in the readings confirms the result.
Clamp-on testing
Fast and non-invasive, but only valid on multi-electrode systems with a genuine parallel return path. On a single isolated electrode a clamp meter will simply be wrong.
Soil resistivity (Wenner four-pin)
Done before design, not after. Four equally spaced pins give apparent resistivity at increasing depths, which determines whether driven rods, deep-bore electrodes or a grid mat is the economic answer for the site.
Send your drawings. Get a compliant system design back.
Share roof plans, structure height and soil data — our team returns a risk assessment summary, air termination or earthing layout, bill of materials and a fixed-price proposal.
- Risk assessment to IS/IEC 62305-2
- IEC 62561 type-tested ARK Make components
- Installation, testing and documented handover