Glossary · Lightning, earthing, fire safety
Separation distance s (lightning protection)
The minimum gap between a PV array and lightning down conductors at which no spark flashes over (DSTU EN 62305-3:2021, cl. 6.3).
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Definition
When lightning current runs down a conductor, a high voltage to earth appears on it. Nearby metal — a PV frame, cables — can see a flashover. DSTU EN 62305-3:2021 (cl. 6.3) sets the separation distance s at which this will not happen:
s = (ki / km) · kc · l| Factor | Values |
|---|---|
| ki — LPS class | I — 0.08; II — 0.06; III–IV — 0.04 |
| km — gap material | air — 1; solid material — 0.5 |
| kc — number of down conductors | 1 — 1; 2 — 0.66; 3 or more — 0.44 |
l is the length along the down conductor from the point where s is computed to the nearest equipotential bonding point. Example: class III LPS, one down conductor, an 8 m building, an air gap: s = 0.04 · 1 · 8 = 0.32 m. With three down conductors the same point needs 0.14 m.
If s cannot be kept, the array is bonded to the LPS, and the DC side then needs a type 1+2 SPD. If the building has no lightning protection, no separation distance is computed; whether one is needed at all is decided by a risk assessment.
How to keep the distance in practice. The usual obstacles are down conductors on the facade near the roof edge and air terminals on the ridge. You can move the array away from them or add down conductors, which brings kc from 1 down to 0.66 or 0.44 and shortens the required distance. If the gap is filled with solid material (brick, concrete), km = 0.5 and the distance doubles. Agree these choices with the lightning protection designer, who knows the LPS class and the down-conductor layout. If the distance is not kept, the frame must be bonded to the LPS with a conductor rated for a partial lightning current.
How Solispec applies it
The Solispec engine computes s by eq. (4) from the LPS class, the number of down conductors and l = building height + array height above the roof, for an air gap. The report shows every factor and the result. If the actual distance is smaller, the engine advises bonding the frame to the lightning protection and fitting a type 1+2 DC SPD (712.534).
Norms and clauses
- DSTU EN 62305-3:2021, cl. 6.3, eq. (4)
Related terms
- Lightning risk assessmentThe DSTU EN 62305-2:2022 calculation deciding whether a building with PV needs external lightning protection; there is no "PV means LPS" rule.
- Surge protective device (SPD)A device that limits lightning and switching surges in PV circuits; its type depends on whether the building has lightning protection.
- PV earthing and equipotential bondingConnecting PV frames, rails and structures to the building’s earthing; under PUE:2026 the earthing must be common with the building.
- DSTU EN 62305-1…4: lightning protection for solar plantsNorms explained
Solispec’s calculation is preliminary: for a design it has to be checked by an engineer. The values and clauses follow the current editions of the norms on the date of the page.