What is IEC 62305?
IEC 62305 is the international standard for protecting structures, people and systems against lightning. This page explains what the standard is: its four parts and their editions, what it covers and what it leaves out, who works with it, and how national versions relate to it.
IEC 62305 is the international standard for protection against lightning.
Published by the International Electrotechnical Commission (IEC) and adopted nationally across India, the Middle East, Africa, Asia, Europe and the UK, it is the reference most of the world uses to decide whether a structure needs lightning protection and how that protection should be designed, installed and maintained.
What sets it apart from older, prescriptive rules is that it works from risk. Instead of applying a fixed rule to every building, you describe the structure and its surroundings, the method estimates how often a strike is likely to cause real harm, and that figure is checked against a level of risk the standard is prepared to tolerate. This page is about the standard itself: its four parts and their editions, its scope, who uses it, and how the national versions relate to it. The method has a guide of its own, the IEC 62305-2 risk assessment, and so do the parts of a lightning protection system.
The four parts of IEC 62305 and their editions
The standard is published in four parts that are read together. Each has its own number, title and edition, and the edition is part of any citation, because clause and table numbers change between editions.
| Part | Title | Current edition | Earlier editions | What it does | Read more |
|---|---|---|---|---|---|
| IEC 62305-1 | General principles | Edition 3, September 2024 | 2006, 2010 | Sets the lightning current parameters, the lightning protection levels LPL I to IV, and the model of sources, causes and types of loss the other parts use | Protection levels |
| IEC 62305-2 | Risk management | Edition 3, September 2024, corrigendum October 2024 | 2006, 2010 | Decides whether protection is needed, by computing the risk R and the frequency of damage F and comparing each with its tolerable value | The risk method |
| IEC 62305-3 | Physical damage and life hazard | Edition 3, September 2024 | 2006, 2010 | Specifies the lightning protection system, its classes I to IV, the components and materials, and inspection and maintenance | The parts of an LPS |
| IEC 62305-4 | Electrical and electronic systems within structures | Edition 3, September 2024 | 2006, 2010 | Protects internal systems from the lightning electromagnetic impulse with zones, coordinated SPDs, shielding and bonding | Protection zones |
Cite a part with its year, for example IEC 62305-2:2024, never the bare number. The third edition revised all four parts at once, and its risk method can give a different answer from the 2010 method on the same building. What changed, item by item, is in what changed in IEC 62305-2:2024, and the terms used across the parts are defined in the lightning protection glossary.
What IEC 62305 covers, and what it leaves out
IEC 62305-1:2024 clause 1 sets the scope of the whole series. It is about keeping lightning from harming a structure, the installations and contents inside it, and the people in and around it. A structure here is broad: an office, a hospital, a tank farm, a telecom shelter and an inverter station all count.
The same clause names what falls outside: railway systems; vehicles, ships, aircraft and offshore installations; buried high-pressure pipelines; and pipe, power and telecom lines that stand apart from the structure. Nuclear power plants are excluded as well. These usually have specialist rules of their own. The clause still treats the series as a minimum for them, and NOTE 1 keeps it in force for any subsidiary structure those rules do not reach. Wind turbines have a dedicated standard, IEC 61400-24, which works alongside the general risk thinking of IEC 62305; the renewable energy guide explains how the two fit together.
IEC 62305 is also a conventional standard. Its protection rests on air terminations placed by the rolling sphere, mesh and protection angle methods. Early streamer emission terminals are covered by other national standards, not by IEC 62305; see ESE air terminals and IEC 62305.
Who uses IEC 62305, and when
An assessment is called for wherever a strike could endanger people, knock out a service, damage a historic building or cause real economic loss, and it is frequently a condition of approval, insurance or a client brief.
The engineers who sign it
Electrical and MEP consultants, lightning-protection specialists and auditors run the assessment and put their name to the result, often as part of a wider electrical or building-services design.
The structures that carry the risk
Data centres, hospitals, industrial and petrochemical plants, telecom towers, warehouses with people, and tall or isolated buildings, where a strike is both more likely and more costly.
The people who rely on it
Building control authorities, insurers, lenders and clients ask for an assessment to the standard, because it shows that a decision about lightning protection was made on evidence rather than assumption.
How national adoptions relate to IEC 62305
Most countries do not use the IEC document directly. A national standards body publishes it under its own number. CENELEC adopts it in Europe as EN IEC 62305, BSI publishes that as BS EN IEC 62305 in the UK, BIS publishes IS/IEC 62305 in India, and Singapore publishes SS 555. An adoption marked identical carries the IEC technical text unchanged; a modified adoption changes some of it and says where.
Two things travel less well than the method. The first is the parameters. IEC 62305-2:2024 lets national or local regulation fix the tolerable risk RT, the tolerable frequency FT and the values in Annexes A, B, C and E, and national annexes often do; see national practice in the annexes. The second is the edition. An adoption follows the IEC text on its own timetable, so SS 555:2018 in Singapore still rests on the 2010 edition, while BS EN IEC 62305 in the UK carries the 2024 one.
The country guides set out each adoption: Germany, Italy, Greece, Spain and Malaysia, with the full list in IEC 62305 around the world.
Not every country adopts it. Australia has its own standard, AS 1768:2021, with a separate risk method, and New Zealand still uses AS/NZS 1768:2007. The United States works to NFPA 780, which leads with how a lightning protection system is installed and carries its risk assessment in an annex; see NFPA 780 vs IEC 62305. Which standard applies to a project is set by the local code, the authority having jurisdiction or the specification, not by preference.
Questions answered
What is IEC 62305?
What are the four parts of IEC 62305?
What is the latest edition of IEC 62305?
Is IEC 62305 the same as EN IEC 62305?
Does every country use the same edition of IEC 62305?
How does IEC 62305 decide whether a structure needs protection?
Who needs an IEC 62305 risk assessment?
What does IEC 62305 not cover?
What are the sources of damage S1 to S4 in IEC 62305?
The tolerable risk in IEC 62305-2 is not a fixed constant.
Clause 7.3 NOTE 1 gives RT = 1 × 10⁻⁵ per year as a
representative value of tolerable risk and adds that another value may be set once
the case has been investigated in detail. The standard's introduction then lets national or local regulations fix
RT, the tolerable frequency of damage FT
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