Computes the horizontal protection radius of a single air-terminal (mast) of a given height, against a rolling sphere of the radius defined by IEC 62305 for the chosen Lightning Protection System (LPS) class — using the same rolling-sphere radii already used in the Lightning Protection calculator for consistency.
Standards followed
IEC 62305 (protection against lightning) — rolling sphere method, Class I=20m, II=30m, III=45m, IV=60m
What it can do
- Protection radius from mast height and LPS class, using rp = √(2Rh − h²) — the geometry of a sphere resting on the ground and just touching the tip of the mast.
- Flags when mast height exceeds the sphere radius (the simple single-mast formula no longer applies and a multi-terminal/mesh study is required).
Example problem
Class III LPS (R=45m), 10m mast.
- rp = √(2×45×10 − 10²) = √(900 − 100) = √800 ≈ 28.28m.
≈28.28m protection radius.
Want the full step-by-step version?
This is the single-mast geometry only — for multiple air terminals, a mesh, or a structure taller than the class's sphere radius, a full multi-point rolling-sphere or mesh-method study is required (not covered by this simple formula).