Lightning Protection (IEC 62305)

Quick pick (TL;DR)

Run a risk assessment (IEC 62305-2) to pick the Lightning Protection Level (LPL I–IV; I is most onerous, for flammable plant).
The LPL fixes the rolling-sphere radius (I=20 m, II=30 m, III=45 m, IV=60 m) and mesh size for the air termination, the down-conductor spacing, and the SPD class.
Provide a low-impedance ring earth (≤10 Ω), bond all metal & services, and fit Type 1+2 SPDs at the LV main.

Step 1 — Level & rolling sphere

LPL	Rolling sphere R	Mesh	Typical
I	20 m	5×5 m	Flammable
II	30 m	10×10 m	Process plant
III	45 m	15×15 m	Ordinary
IV	60 m	20×20 m	Low risk

Step 2 — Worked screen

Process building → LPL II

Step 1 — Risk → level flammable contents, IEC 62305-2 risk R > tolerable → select LPL II Step 2 — Air termination rolling sphere R = 30 m (LPL II) mesh on roof = 10 × 10 m rods at corners/high points Step 3 — Down-conductors spacing = 10 m around perimeter (LPL II) Step 4 — Earth & SPD Type B ring earth ≤ 10 Ω Type 1+2 SPD at LV main Answer → LPL II: R30, mesh 10 m, DC @10 m, SPD 1+2

Rolling sphere of radius R touches where air terminals are needed; all parts must match the same LPL.

Step 3 — Earthing & SPD

Ring earth ≤ 10 Ω, interconnected.
Bond all metal & services.
SPD Type 1+2 (+3 at equipment).

Common mistakes

LPL not from risk assessment.
Air termination only, no SPDs.
High earth resistance / unbonded metal.

Requisition & datasheet

Structure, risk, LPL.
Air termination, conductors, earth, SPD.

Frequently asked questions

What should I know about Lightning Protection (IEC 62305)?

Run a risk assessment (IEC 62305-2) to pick the Lightning Protection Level (LPL I–IV; I is most onerous, for flammable plant). The LPL fixes the rolling-sphere radius (I=20 m, II=30 m, III=45 m, IV=60 m) and mesh size for the air termination, the down-conductor spacing, and the SPD class. Provide a low-impedance ring earth (≤10 Ω), bond all metal & services, and fit Type 1+2 SPDs at the LV main.

Which standards or codes apply?

IEC 62305 (-1 general, -2 risk, -3 physical damage, -4 electrical/electronic), NFPA 780, API RP 545 (tanks).

Standards — IEC 62305 (1–4); NFPA 780; API RP 545.