Rolling Sphere Method Calculator -

: Never trust manual approximations for critical infrastructure. Run the rolling sphere simulation, verify the red zones, and then build with confidence. About the author: This article is based on principles from IEC 62305 and IEEE 998. Always consult local codes and a licensed engineer for final designs.

The sphere’s radius is not arbitrary. It is derived from the formula, which relates to the peak lightning current. The most common standard (IEC 62305 and NFPA 780) defines protection levels (I to IV) with corresponding sphere radii: rolling sphere method calculator

A smaller sphere (Level I) is more "touchy" and will probe into every crevice, providing the highest level of protection. A larger sphere (Level IV) offers less stringent protection, suitable for ordinary structures. The Core Equation To determine if a point at height ( H ) is protected by a lightning mast of height ( h ) (with ( h > H )), the horizontal distance ( d ) from the mast to the point must satisfy: Always consult local codes and a licensed engineer

Introduction

For decades, the protection of structures against direct lightning strikes has relied on a few key geometric models. Among them, the stands out as the most intuitive and physically accurate representation of how lightning intercepts a structure. Unlike the older "cone of protection" method, RSM accounts for the actual striking distance of lightning, making it indispensable for protecting complex or sensitive facilities like substations, data centers, petrochemical plants, and tall buildings. The most common standard (IEC 62305 and NFPA

: Using the formula, the maximum distance is ≈ 18.7 m.