Chemical earthing and earth resistance

Chemical earthing is an earthing method in which the electrode (GI or copper-bonded rod/pipe) is surrounded by a conductive chemical compound (bentonite, graphite-based or other earth-enhancing compound) instead of the traditional salt and charcoal, to obtain a low and stable earth resistance with little maintenance.

Chemical earthing

• A pit or bore is made and the electrode is placed in the centre.
• The space around it is filled with earth-enhancing compound (e.g. bentonite clay mixed with graphite/carbon), which absorbs and holds moisture and has very low resistivity.
• Advantages: low resistance even in rocky or dry soil, stable value through seasons, no need for regular watering, longer life with less corrosion, compact.
• Used in telecom towers, substations, data centres and buildings where soil is poor.

Factors affecting earth resistance

1. Soil resistivity: the main factor; clay and loam have low resistivity, sand, gravel and rock very high.
2. Moisture content: resistivity falls sharply as moisture rises (dry soil can be 10 to 100 times worse).
3. Salt (chemical) content: dissolved salts increase conductivity.
4. Temperature: resistivity rises as temperature falls, and very sharply when soil freezes.
5. Electrode size and depth: longer and deeper electrodes reach moist, stable soil layers and have lower resistance.
6. Number and spacing of electrodes: electrodes in parallel, spaced at least twice their length apart, lower the combined resistance.
7. Contact between electrode and soil: loose backfill, voids or corrosion raise resistance.
8. Soil compaction and grain size: compact, fine-grained soil gives better contact.

Example: a 3 m copper-bonded rod in dry sandy soil may give 40–50 Ω; with chemical backfill the same rod can give below 5 Ω.