| Primary value | 30 m radius (Class III IS/IEC 62305 · 60 m for Class IV) |
| Applies to | Buildings ≥ 23 m height (NBC 2016 mandatory) · Buildings on hills or isolated sites with no taller neighbours · Industrial structures handling flammable / explosive materials |
| Exceptions | Class I — most-critical (hospitals, ammunition) → 20 m radius |
| Class II — high-importance (commercial, telecom) → 30 m radius | |
| Class III — common buildings → 45 m radius | |
| Class IV — low-risk → 60 m radius | |
| Air terminal projection above roof → ≥ 250 mm | |
| Down conductor count → ≥ 2 (one at each diagonal corner) | |
| Earth electrode resistance → ≤ 10 Ω | |
| Measured as | Radius of the protective zone at ground level when the air terminal sits on top of the building. The protective cone is generated by a rolling sphere of radius depending on protection class. |
| Source | IS / IEC 62305 — Part 3 📚 Cross-referenced |
17 related items across IS codes, knowledge articles, design rules, maps and tools
NBC 2016 makes lightning protection mandatory for any building above 23 m. The protective radius is what determines whether one rod covers the building or you need a mesh / multiple finials — a single 5 m air terminal on a 25 m × 25 m building only covers ~30 m radius (Class II), so a square plot of that size is just barely protected by one rod at the centre.
Most Indian high-rises are designed to Class II (30 m radius). For a typical 30 × 30 m floor plate, two air terminals — one at each diagonal corner — give overlapping protection. Down conductors run inside the structural columns to a buried 25 mm × 3 mm copper / GI strip earth ring with multiple electrodes ≤ 10 Ω.