KSA averages 5–25 thunderstorm-days per year and rising. A 100 m structure can take a 100 kA strike; the difference between a controlled discharge and a fire on the roof is the LPL class, the air-termination geometry, the down-conductor count, and the earth grid. IEC 62305 frames all four in a single risk-assessment workflow.
Four ideas that close the gap between SPDs and a real LPS.
A Lightning Protection System catches the direct strike on the roof and conducts it to earth. Surge Protective Devices clip the residual transient on the cables. You need both.
IEC 62305-2 walks through structural risk (R1), service risk (R2/R3), cultural-heritage (R4). The output is LPL I (highest, banks/hospitals) to LPL IV (low-risk warehouse).
A virtual sphere of radius 20–60 m (depending on LPL) rolls over the roof. Anywhere it touches needs a finial, mesh, or natural component. Anywhere it does not touch is protected.
LPL I = 10 m spacing. LPL IV = 20 m. A corner building always needs a conductor at each corner, regardless of perimeter math.
IEC 62305-1 Table 5.
| LPL | Peak current | Rolling sphere r | Mesh size | Down-conductor spacing |
|---|---|---|---|---|
| I | 200 kA | 20 m | 5 × 5 m | 10 m |
| II | 150 kA | 30 m | 10 × 10 m | 10 m |
| III | 100 kA | 45 m | 15 × 15 m | 15 m |
| IV | 100 kA | 60 m | 20 × 20 m | 20 m |
| SPD Type 1 | – | – | – | At service entry |
| SPD Type 2/3 | – | – | – | DB / end-use coordination |
Six engineering decisions behind every IEC 62305-compliant design.
IEC 62305-2 sums probability of strike (from ground flash density Ng, structure size, location factors) and consequence (fire load, occupants, services lost). If the calculated risk R1 exceeds the tolerable RT (typically 10⁻⁵), an LPS at a given LPL is required. KSA risk maps: Asir highlands 8+ flashes/km²/year; Riyadh 1–2; coastal 3–4.
Three protection methods. Finials (Franklin rods) on tall structures. Mesh across flat roofs. Natural components (steel I-beams, rebar) if the conductive path is continuous and verified. Most KSA towers use a mesh on the roof plus finials on equipment.
Minimum two down conductors per building, spaced per LPL. Run them straight, no 90° bends sharper than the standard allows, into a perimeter earth electrode loop. Reinforcing bar can substitute if continuity is bonded and tested.
Type A: vertical rods or horizontal radials at each down conductor. Cheaper, works on resistive soil. Type B: foundation ring electrode (Ufer ground / concrete-encased rebar). More effective on rocky terrain, mandatory for LPL I structures, and almost always cheapest in new construction because the rebar is already there.
Even a perfect LPS lets transient overvoltages into the building via the bonded mass. Type 1 SPD at the main panel handles the 10/350 µs lightning current waveform. Type 2 at sub-distribution clips the 8/20 µs residual. Type 3 at sensitive loads (servers, BMS) gets the last bit. Skip the coordination study and you blow up your IT room on the strike that "the lightning rod handled."
Early Streamer Emission air terminals (NF C 17-102, French) claim larger protection radii than IEC 62305 allows. Independent tests are inconclusive at best. IEC 62305 does not recognise ESE devices, and Saudi consultants on Vision-2030 projects increasingly write "IEC 62305 only, no ESE" into the spec. If your supplier offers an ESE solution, ask for the IEC equivalent design before approving.
NLC supplies coordinated Type 1/2/3 SPDs alongside our switchgear, with LPS interface drawings and bonding details to IEC 62305 / SBC 401.
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