An earthing grid, or earth mat, is a network of conductors buried under and around a site, connected to several earth electrodes. Where a single earth pit is enough for a house, a substation, factory or large solar plant needs a grid.
Why a grid instead of separate pits
- Lower overall resistance. Many conductors and electrodes in parallel give a far lower resistance than any one pit.
- Safe step and touch voltages. During a fault, the ground around equipment rises in voltage. A grid keeps the whole area at nearly the same potential, so a person standing or touching equipment is not exposed to a dangerous difference.
- Reliability. If one connection fails, current still has other paths.
- One reference for everything. Transformers, panels, structures, fences and lightning protection all bond to the same grid.
Where earthing grids are used
High-tension substations, power plants, industrial units with large motors and transformers, solar parks, telecom sites and data centres. Our high-tension works page describes the projects we take on.
How a grid is designed
Design starts with a soil resistivity test, usually by the Wenner four-pin method, and the maximum fault current and clearing time of the system. From these, the designer works out conductor size, mesh spacing, depth and the number of electrodes, following IS 3043 and, for substations, IEEE 80. The result is checked against the target resistance and the permissible step and touch voltages.
Materials
| Part | Typical material |
|---|---|
| Grid conductors | G.I strip or copper strip, sized for the fault current |
| Electrodes | Chemical earthing electrodes at the perimeter and key points |
| Backfill | Earthing compound around electrodes |
| Joints | Welded, exothermic or bolted with suitable clamps |
| Test points | Inspection pits with pit covers |
| Equipment risers | Strip or flexible copper cable to each item |
Testing and handover
Once built, the grid resistance is measured and recorded, and continuity between the grid and each piece of equipment is checked. Re-testing at regular intervals catches corroded joints before they matter.
Vivek Earthing manufactures grid materials in Howrah, cut to your drawing, and installs and tests complete grids. Send us your single-line diagram or layout for a quotation.