IS/IEC 62305 Lightning Protection Design: A Practical Guide for Indian Projects

Start with risk, not with rods

IS/IEC 62305-2 requires a quantified risk assessment before any hardware is selected. The assessment compares calculated risk R1 (loss of human life) against the tolerable risk RT of 10⁻⁵, using strike density, collection area, structure use, and internal system sensitivity.

The output of that calculation is a Lightning Protection Level (LPL I to IV), which in turn fixes the rolling sphere radius, mesh size, and down conductor spacing for the project.

From protection level to layout

LPL I uses a 20 m rolling sphere with a 5x5 m mesh and 10 m down conductor spacing; LPL IV relaxes to 60 m, 20x20 m and 20 m respectively. Data centres, pharma plants and explosive atmospheres almost always land at LPL I or II.

Model the rolling sphere across the actual roof geometry — parapets, chillers, antennas and lift machine rooms are the surfaces that get struck, and each needs either a terminal or a bonded conductive path.

Documentation that survives an audit

A compliant handover pack contains the risk assessment, air termination drawings, down conductor routing, earth resistance test records for each electrode, continuity readings across every test link, and material test certificates to IEC 62561.