Rolling Sphere — Method Calculator

: How far can the arrester be from the mast?

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

| 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) | : How far can the arrester be from the mast

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