Free Web Tool · PEC / NFPA 780

Lightning Protection

Rolling-sphere zone of protection and a simplified risk-assessment to recommend a Lightning Protection Level (LPL I–IV) per PEC / NFPA 780 / IEC 62305.

Input

Results

Rolling-sphere R for selected LPL
Half-base radius of cone, r
Equivalent collection area Ad
Expected strikes/yr (Nd)
Risk acceptable (≤ 10⁻⁵)?
Method

Rolling-sphere radius R: LPL I = 20 m, II = 30, III = 45, IV = 60. For an air-terminal at height h with object below at height h_g (h > h_g), the protected horizontal radius r = √[(R−h_g)·(2h−h_g) − (h−h_g)²] when 2R > h. IEC 62305: Ad = L·W + 2·(L+W)·3·H + π·(3·H)². Nd = Ng·Ad·1e−6·C2·C3·C4·C5.