Glossary · Lightning, earthing, fire safety
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.
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Definition
Long DC cables on a roof act as an antenna: a nearby lightning strike induces a pulse in them that can break down the inverter input. A surge protective device (SPD) diverts that pulse to earth. DBN V.2.5-23:2025 (cl. 8.6) requires protection against lightning and induced surges with SPDs per DSTU EN 62305-4:2012 and the device standards.
For the PV part, section 712.534 of DSTU HD 60364-7-712:2022 sets where and which SPDs go. The key question is whether the building has external lightning protection (LPS). If it does, the array either keeps the separation distance from the down conductors or is bonded to the LPS, and then part of the lightning current can flow through its circuits. In that case the DC side needs a type 1+2 SPD and a 16 mm² Cu bonding conductor (cl. 712.534.101, 712.534.105).
An SPD does not replace earthing: without a short path to the main earthing bar it has nowhere to send the pulse. And the need for external lightning protection is decided by a risk assessment, not by the presence of a PV array.
Where SPDs go. Usually at the inverter DC input or in a DC combiner next to it, and on the AC side in the building's distribution board, since the inverter is tied to the grid as well. A DC SPD's rated voltage must match the string's UOC MAX. Keep the conductor from the SPD to the earthing bar as short as possible and without loops. The device type depends on the building's lightning protection: without an LPS, or with the separation distance kept, the requirements are milder than when the frame is bonded to the LPS. The final choice of devices and locations is made in the electrician's design.
How Solispec applies it
When the Solispec constructor is told the building has lightning protection, the electrical check adds a line: separation distance per DSTU EN 62305-3:2021 or bonding to the LPS, SPD type 1+2, 16 mm² Cu conductor (712.534.101, 712.534.105). The report’s fire and lightning section computes the separation distance from your inputs and, if it is not met, advises bonding the frame to the LPS and fitting a type 1+2 DC SPD.
Norms and clauses
- DBN V.2.5-23:2025, cl. 8.6
- DSTU EN 62305-4:2012
- DSTU HD 60364-7-712:2022, cl. 712.534.101, 712.534.105
Related terms
- 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).
- 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.
- 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.
- PV DC cableThe cable between the panels and the inverter; its section is chosen by I_SC MAX at 70 °C and checked for voltage drop.
- DBN V.2.5-23:2025 (from 01.01.2026): what applies to solarNorms explained
- DSTU EN 62305-1…4: lightning protection for solar plantsNorms explained
- DSTU HD 60364-7-712:2022: the electrics of PV systemsNorms 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.