Rolling sphere zone of protection, down conductor spacing, and tank earthing/bonding (OISD-GDN-180)
◉ OISD-GDN-180 (2018 REVISION) STYLE CHECK · NOT A REGULATORY SUBMISSION TOOL
⚠ Indicative tool only. Rates, tables, and the rolling-sphere geometry checked directly against the standard's page images. The zone-of-protection formula below is derived from the rolling-sphere tangency geometry the standard itself defines in text ("space not intruded by a rolling sphere...resting against a lightning protection air termination") — it's not printed as an equation in the source, which presents it as Figure 1 instead. I verified the derivation reproduces that figure's curves exactly at several points (including the labeled "22.5" curve crossing y=15 at x≈3, matching the derivation to within reading precision) before using it here. Earthing resistance values are NOT covered — the standard itself defers those to a separate document (OISD-STD-137), which isn't available to build from.
Identification
Research entries stay private to you for practice/testing. Switch to Official once this is a real design your company should see.
Design Basis
Striking distance of 30m is stated for structures containing flammable materials; 60m for other structures (§4.2 note). Class selection is a convenience default — override R directly if your risk assessment (IS/IEC 62305-2) calls for something else.
Self-Protection Check (§7.1, §7.2)
Result Not evaluated
Minimum roof thickness for self-protection3/16 in. (4.8 mm)
Determination—
Zone of Protection — Rolling Sphere (Fig. 1 relationship)
For an air terminal of height H and rolling sphere radius R, the protected horizontal distance at a given height y on an adjacent lower object.
Height y (m)
Protected Horizontal Distance (m)
Result
Ground-level protected reach (y=0)—
Down Conductor Spacing (§5.1.2)
Result
Typical spacing for selected LPS class—
Tank circumference—
Minimum number of down conductors—
Tank Earthing Connections (Table-A, Fig. 8)
Verified to exactly reproduce Table-A: N = max(2, ⌈πD/30⌉), i.e. maximum 30m spacing around the perimeter with a minimum of 2 — confirmed against every row from D<15m through 85≤D<95m.