Earthing flat, earthing strip and earthing patti all mean the same thing - a flat bar conductor used for earthing. An earthing flat size is width x thickness in millimetres, the common ones being 25 x 3, 25 x 6, 32 x 6, 50 x 6 and 65 x 10 mm in GI, and 25 x 3 to 50 x 6 mm in copper.
Standard earthing flat sizes
| Earthing flat size (mm) | Typical use |
|---|---|
| 25 x 3 | Panels and sub-distribution |
| 25 x 6 / 32 x 6 | Distribution and machinery bonding |
| 50 x 6 | Main earth grid and risers |
| 65 x 10 | Substations and power plants |
Flat vs round earth conductor
A flat has more surface area than a round wire of the same cross-section, so it dissipates heat and high-frequency surge current better - which is why flats are preferred for earth grids and lightning down-conductors. Round conductors are used where routing is easier. Size either by the fault current per IS 3043; see the strip size chart.
