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BS EN 62305
explained

The four parts, and what 2024 changed.

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What it is

BS EN IEC 62305 is the British and international standard for protection against lightning. It is published in four parts and covers the whole process, from deciding whether a structure needs protecting through to inspecting the finished system. It replaced BS 6651, which was withdrawn in 2008, and the current edition of the series was published in 2024.

The standard matters to building owners for a practical reason. It is the reference point everyone else uses. Your designer works to it, your insurer expects it, and if a system is ever questioned after an incident it is the document the question gets measured against.

The four parts

  • Part 1, general principles. Defines the lightning protection levels, the protection zones and the lightning currents each level is designed against.
  • Part 2, risk management. The calculation that decides whether protection is needed and to which class, assessed across loss of life, loss of service, loss of cultural heritage and economic loss.
  • Part 3, physical damage and life hazard. The system itself. Air termination, down conductors, earth termination, materials, separation distances, and inspection and maintenance.
  • Part 4, electrical and electronic systems. Protecting what is inside the building against the lightning electromagnetic impulse, including surge protective device selection and coordination.

What 2024 changed

The 2024 edition is a full revision rather than an amendment, and two of the changes affect the numbers a risk assessment produces. Part 2 introduced a single risk that combines loss of human life with loss caused by fire, and replaced lightning strike density with ground impact point density as the basis for estimating how many hazardous events to expect.

Part 1 tightened how surge currents are specified for sizing surge protective devices on low voltage power and telecoms systems, and pointed to the BS EN IEC 62561 series for components. Part 3 added minimum metal thicknesses for air termination systems where puncture and hot spots are a concern. Part 4 gained new guidance on current sharing, including in photovoltaic installations.

The practical point for a building owner is that an assessment produced under the older edition may not give the same answer today. If you are relying on a report written before 2024 to justify the protection you have, it is worth revisiting.

Protection levels

The standard defines four lightning protection levels, LPL I to LPL IV. Level I is the most demanding, designed against the widest range of lightning currents, with the tightest air termination mesh and the closest spacing of down conductors. Level IV is the least demanding.

Which level a structure needs is an output of the Part 2 risk assessment, not a choice. A building holding something irreplaceable, or where a strike would endanger life, will land at a higher level than a low occupancy building of identical height.

Get a risk assessment

Inspection intervals

Part 3 sets maximum intervals between inspections, and they depend on the protection class of the system.

  • Class I and II. Visual inspection every year. Complete inspection every two years.
  • Class III and IV. Visual inspection every two years. Complete inspection every four years.
  • Structures with a risk of explosion. More frequently than either of the above.

Those are ceilings, not targets. UK practice is a full test every eleven months, because that keeps the certificate inside a twelve month insurance window and moves the test through the seasons so ground conditions are not always measured in the same weather.

How often should you test?

Common questions

Is BS EN 62305 a legal requirement?

BS EN IEC 62305 is a standard, not legislation, so it is not directly enforceable in the way an Act or a set of Regulations is. It becomes binding in practice through other routes: as the standard a designer works to, as the benchmark for demonstrating a duty of care, as a condition of insurance, and as the reference point for the maintenance duty under the Electricity at Work Regulations 1989.

What is the British standard for lightning protection?

BS EN IEC 62305, published in four parts. It replaced BS 6651, which was withdrawn in 2008. The current edition of the series was published in 2024 and supersedes the 2011 version.

What is the difference between BS 6651 and BS EN 62305?

BS 6651 used a simpler risk calculation and treated surge protection as largely advisory. BS EN 62305 assesses risk across four separate loss categories, brings protection of internal electrical and electronic systems into the main standard, and sets four defined protection levels with their own construction requirements. A system that satisfied BS 6651 will not automatically satisfy BS EN 62305.

What are the four lightning protection levels?

LPL I to LPL IV. Level I gives the highest protection and is designed against the widest range of lightning currents, up to around 200 kA, with the tightest air termination mesh and the closest down conductor spacing. Level IV gives the lowest. The level required for a particular structure comes out of the Part 2 risk assessment, not from preference.

Which part of BS EN 62305 covers testing?

Part 3. As well as the physical design of the air termination, down conductor and earth termination systems, Part 3 covers inspection and maintenance, including the maximum intervals between inspections for each protection class.

Need advice?

If you have been told your building does not comply, send us what you have been told and we will tell you whether it is right. Call 01892 667258.

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