ČSN EN IEC 62305 ed. 3: What Changes

The call from the contractor is usually brief: “A new lightning protection standard has been published, so your industrial building will need to be upgraded.” Two days later, a quotation lands in your inbox, including a charge for recalculations that nobody had mentioned before. The series of lightning protection standards has indeed been redesignated and issued in a third edition. But between “a new standard has been published” and “you must rebuild your completed lightning protection system” lies a chain of assumptions, most of which do not hold in the Czech legal environment.

This article answers one question: what does edition 3 mean for a lightning protection system that is already installed on a building? Whether you need lightning protection at all, how risk assessment works and what the protection classes mean are covered separately in our article on lightning protection according to ČSN EN 62305.

What has been published and when it takes effect

The designation has changed from ČSN EN 62305 to ČSN EN IEC 62305 ed. 3. “IEC” has been added to the title as a formal consequence of how the European standard is adopted. This is a continuation of the same series, not a standard from an entirely different system. Its individual parts were published at different times, which is why quotations and inspection reports may refer to different dates.

For Parts 2 and 4, check the exact date in the Věstník ÚNMZ or the agentura ČAS catalogue. The publication date and effective date are not the same, and even industry professionals sometimes confuse them when a standard is released in stages. When lightning protection is required and what it must meet regardless of the edition are summarised in our main article on the ČSN EN 62305 lightning protection standard.

The date that matters most, however, is different: the published parts state that the second edition remains concurrently valid until 31 October 2027. Until then, both editions exist side by side. After that date, the existing edition will be withdrawn and edition 3 will remain the current valid standard—the usual means of demonstrating that a solution has been designed correctly. Using the withdrawn edition will not automatically be prohibited, because a Czech technical standard is not generally binding. However, the designer will need to provide a professional justification and demonstrate that the solution meets the legal requirements. When commissioning a design, ask for the specific designation: “according to ČSN EN 62305” is no longer an unambiguous brief.

A standard is not a law, and the regulation addresses design

For a completed and functional lightning protection system, the new edition does not in itself require the air-termination system to be rebuilt, additional down conductors to be installed or the earthing arrangement to be changed. This does not mean that the system’s condition should not be assessed. It only means that publication of the standard is not the trigger. This rests on two points worth knowing, as they can be used when discussing the matter with a contractor.

A Czech technical standard is not generally binding. This is stated directly in § 4 odst. 1 zákona č. 22/1997 Sb., and publication of a new edition does not change it. The role of a standard is then clarified by two further, separate considerations. The first is how a legal regulation refers to the standard. The reference may be exclusive—the regulation may require compliance with a specific standard, as § 16 vyhlášky č. 146/2024 Sb. does with the wording “musí být navrženy a provedeny v souladu s normou uvedenou v příloze č. 14”—or merely indicative, in which case, under § 4a odst. 3 zákona č. 22/1997 Sb., compliance with a harmonised or designated standard is deemed to satisfy the requirements to the extent and under the conditions specified by the technical regulation, without prohibiting another demonstrably compliant solution. The second consideration is your own contractual position: the design brief, the contract with the supplier or the insurance terms may require compliance with a specific edition. In practice, this is the most common reason why a standard “must” be followed. It is, however, a contractual obligation owed to another party and does not alter the fact that the standard is not generally binding.

The building regulation applies at the design and construction stage. Lightning protection in construction is governed by vyhláška č. 146/2024 Sb. o požadavcích na výstavbu (effective from 1 July 2024, replacing vyhláška č. 268/2009 Sb.). Its § 26 requires lightning protection to be “navržena a provedena” for facilities storing or producing explosive and flammable substances, above-ground parts of designated gas installations, and wherever a strike could endanger the life or health of people or animals or cause substantial damage. The requirement is expressed in functional terms: příloha č. 14 vyhlášky, which lists the ČSN standards associated with individual provisions, does not specify any standard for § 26, and the designation 62305 does not appear in the regulation. The wording concerns design and construction; it does not impose an obligation to retrospectively alter a building that was lawfully constructed according to the state of knowledge at the time.

Operation is a third, separate area. A lightning protection system is classified as designated electrical technical equipment. Nařízení vlády č. 190/2022 Sb. includes equipment for protection against atmospheric and static electricity among designated equipment in § 3 odst. 1, while § 7 odst. 5 písm. d) links the intervals for periodic inspections to příloha č. 4. This regime applies to operators under zákon č. 250/2021 Sb., meaning legal entities and self-employed individuals. For a privately used family home, the obligations are determined primarily by building law and the insurance contract. The intervals depend on the LPS protection class, not on the edition of the standard, and the new edition does not alter them. We explain them in detail in our article on lightning protection inspection intervals.

In practical terms, the expiry of concurrent validity does not in itself require alterations to an industrial building approved for use in 2016 with a lightning protection system designed to the second edition. Withdrawal of the standard does not invalidate an installation built according to it. This does not automatically mean that everything is satisfactory, however. That can only be determined through an individual assessment of the system’s actual condition, the changes made to the building and its use since installation, and the requirements currently imposed by law. An inspection assesses the actual condition—corrosion where a conductor enters the ground, broken connections, a test joint concealed beneath external insulation, or new metal structures on the roof. Compliance with the original design does not in itself guarantee safety.

When edition 3 will actually affect you

The transition period is not about whether the building must be altered. It determines which edition will be used for a new design. Edition 3 will affect your building in the following situations:

• A new building, extension or additional storey. Until 31 October 2027, the designer may use either edition. After that date, edition 3 will be the valid edition, and using the withdrawn edition will require a specific professional justification.
• Refurbishment affecting the roof or building envelope. This includes new roofing, thermal insulation, replacement of sheet-metal elements or replacement of an industrial building’s cladding. Down conductors must be reattached and the air-termination system reinstalled. The designer will determine which edition should be used to recalculate that part, taking account of the design date, scope of the work, transitional provisions, continuity with the existing documentation and contractual brief. Parts from different editions of the series should not be mixed without proper control.
• Installation of a photovoltaic system. This is the most common trigger. Panels and their supporting structures occupy an area originally designed to remain empty, while also adding conductive components and DC cable routes. The air-termination system’s protected volume and separation distance must be recalculated, and surge protection must be addressed on both the DC and AC sides. This must be dealt with in the design before installation, not afterwards in the inspection report. We explain the wider context in our article on the fire safety of rooftop photovoltaic systems.
• A change in use or internal technology. A warehouse becomes a production facility, or a server room, cooling system or EPS is added. This changes the inputs to the risk assessment under Part 2—and therefore its outcome.
• After a lightning strike or severe storm. An exceptional inspection is not concerned with the edition, but the technician will usually also consider whether the original design remains suitable for the building’s current use.

The difference between “do nothing” and “recalculate” is therefore not a date on the calendar, but an alteration to the building:

We provide lightning protection inspections and assessments following roof alterations for companies, owners’ associations and municipalities. If you do not have your own technician and do not want to guess whether a recalculation is necessary, we will assess it for you and explain what it means for your next inspection.

What has substantively changed in edition 3

The changes are not merely cosmetic, but neither are they revolutionary. The main points identified in the available summaries are as follows.

Part 1 aligns its definitions with developments in IEC and adds information on lightning current parameters for laboratory testing of components. It distinguishes public-interest services—such as hospitals, energy infrastructure and water utilities—from other structures. For public-interest services, the authority with the relevant powers determines the required level of protection; for other structures, the decision remains with the owner. It introduces the evaluation of damage frequency against a tolerable value, focusing on the operational availability of internal systems. The sizing of surge protective devices for individual sources of damage has also been refined.

Part 3 adjusts practical design rules. It refines the calculation of separation distance, adds minimum thicknesses for metal sheets and pipes where melt-through must be prevented, refers to the series governing LPS components and adds annexes on topics that were previously insufficiently addressed—green roofs and the protection of high-rise façades. A green roof on an office building is no longer unusual, yet the question of how to route the air-termination system through the substrate has until now often been left to improvised solutions.

Part 4 introduces stricter requirements for the coordination of surge protective devices and the shielding of cable routes inside the structure. For a company operating production controls, a server room or photovoltaic inverters, this is the part of the series with the greatest practical impact—and also the area where savings made during installation may only become apparent after the first storm.

The reference to the series of standards for lightning protection system components (ČSN EN IEC 62561) is more relevant to building owners than it might appear. It shifts the emphasis from “something was welded into place” to components with documented test performance, including clamps, connectors and earth electrodes. For a lightning protection system repaired after installation, this has one very specific consequence: it determines what should appear on the delivery note when a company replaces ten clamps.

Five things to request at your next inspection

1. The basis on which the LPS was installed. The report should state the edition and the year of the design, not merely “ČSN EN 62305”. Without this information, it is unclear which benchmark the technician used.
2. A distinction between a defect and a deviation from the new edition. A broken down conductor is a defect. A solution that complies with the original design but would be designed differently today is not necessarily a defect in itself. If the technician finds that the system is unsafe in its actual condition or for the building’s current use, however, it is a defect regardless of what the original design says. Conversely, a deviation from the new edition that has no safety impact should be recorded as a justified recommendation. If the report merely lists non-conformities with edition 3, ask for references to the specific provisions and an explanation.
3. Measured values in a table, compared with the previous report. Without figures, increasing earth electrode resistance cannot be identified—and with earthing systems, the trend often reveals more than a single measurement.
4. A record of changes to the building since the last inspection. Photovoltaic panels, air-conditioning units, antennas, new roofing or thermal insulation.
5. An assessment of the separation distance if anything has been added to the roof.

If the lightning protection design is missing—a common situation with buildings from the 1980s and 1990s—you face a more serious problem than the edition of the standard. The technician has no baseline against which to compare the system, and the report will include a reservation concerning the limited scope of the assessment. We explain how to locate and supplement the necessary records in our article on lightning protection documentation for an older building.

What to do by 31 October 2027

Three steps, with no additional investment required.

1. Find out which requirements your LPS was built to meet. Is there a design? A recent inspection report? A risk assessment specifying the protection class? These are the only records that carry weight in a dispute. Property insurance terms commonly require equipment to be maintained in accordance with applicable requirements and inspection records to be produced, but the specific regime follows from the contract, not from the standard.

2. For planned building work and photovoltaic installations, specify the edition in the brief in advance, even though both editions are permitted during the transition period. The choice is the designer’s: it will be assessed according to the design date, scope of the change, transitional provisions and continuity with the existing documentation. The contractual brief is nevertheless one of the inputs, so the contract should state the requirement unambiguously, and parts from different editions should not be mixed arbitrarily. A design prepared today under the old edition may create additional work the next time the building is altered.

3. For photovoltaic installations, follow the sequence assessment → installation → inspection. The effect of the photovoltaic system on the air-termination system, separation distance, bonding and surge protection must be resolved professionally before installation by coordinating the LPS design with the photovoltaic design. A subsequent inspection cannot replace either the design or this coordination. Only after installation should the relevant initial inspection of the electrical installation—and, where appropriate, an exceptional inspection of the LPS—take place. Do not schedule a periodic lightning protection inspection immediately before work on the roof: the system will have to be assessed again after the work.

The new edition does not in itself change the scope of a periodic inspection. Recalculating the LPS because of a photovoltaic installation or refurbishment is, however, separate design work rather than an item in the inspection report, so allow for it separately in the construction budget.

Sources used for this article

• Lightning protection inspections – a service provided by SOHE.
• Lightning protection according to ČSN EN 62305: when it is required and what it must meet – when the obligation arises, how risk assessment works and what the protection classes mean.
• Lightning protection inspections: how often under ČSN EN 62305 – intervals for periodic inspections and visual checks according to the protection class and type of building.
• Lightning protection documentation for an older building – what to do when the design is missing and the technician has no baseline against which to compare the system.
• Zákon č. 22/1997 Sb. – o technických požadavcích na výrobky; § 4 odst. 1 states that a Czech technical standard is not generally binding, while § 4a odst. 3 governs the effect of references to harmonised or designated standards.
• Zákon č. 250/2021 Sb. – o bezpečnosti práce v souvislosti s provozem vyhrazených technických zařízení; defines the operator’s obligations.
• Nařízení vlády č. 190/2022 Sb. – o vyhrazených technických elektrických zařízeních; § 3 odst. 1 includes protection against atmospheric electricity, while § 7 odst. 5 písm. d) together with příloha č. 4 specifies periodic inspection intervals.
• Vyhláška č. 146/2024 Sb. – o požadavcích na výstavbu; § 26 concerns the design and installation of lightning protection, while příloha č. 14, which lists the ČSN standards associated with individual provisions of the regulation, specifies no standard for this section.
• ČSN EN IEC 62305 ed. 3, Parts 1 to 4 (and the existing ČSN EN 62305 ed. 2), together with the ČSN EN IEC 62561 series for lightning protection system components. The standards are not available free of charge and are sold by agentura ČAS.

This article is for information only and does not constitute legal advice. The specific lightning protection regime and inspection intervals must be determined according to actual operations, the manufacturer’s documentation, the operating environment and the risk assessment.

Not sure which requirements your lightning protection system was built to meet or whether the transition to edition 3 affects you at all? We will examine the documentation and the roof, then explain exactly what it means for your next inspection. We provide lightning protection inspections for companies, owners’ associations and municipalities. Send us a no-obligation enquiry or email info@sohe.cz. If you are planning a photovoltaic installation or roof refurbishment, contact us sooner rather than later: a recalculation commissioned in advance costs less than alterations to a completed façade.