Rolling Sphere Method Calculator May 2026

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:

[ d \leq \sqrtr^2 - (h - r)^2 - \sqrtr^2 - (H - r)^2 ] rolling sphere method calculator

But manual RSM calculations are tedious and error-prone. Enter the —a digital tool that transforms complex 3D geometry into actionable protection zones. This article explains the physics behind the method and how to leverage a calculator for real-world designs. The Physics: Why a Sphere? The Rolling Sphere Method is based on a simple premise: Imagine a sphere of a fixed radius, ( r ), rolling over the terrain and over the structure in question. Where the sphere touches the ground or a lightning protection system (LPS), it represents a point a lightning leader could attach. Any volume that the sphere cannot touch (because it is shielded by a mast, air terminal, or the ground itself) is considered protected. A smaller sphere (Level I) is more "touchy"

| Protection Level | Peak Current (kA) | Rolling Sphere Radius (r) | | :--- | :--- | :--- | | Level I (Highest) | 3 kA | 20 m (66 ft) | | Level II | 5 kA | 30 m (98 ft) | | Level III | 10 kA | 45 m (148 ft) | | Level IV (Lowest) | 16 kA | 60 m (197 ft) | Enter the —a digital tool that transforms complex

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:

Introduction