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BS EN 62305 – Main Considerations

BS EN 62305 Risk Assessment PDF

At Omega we pride ourselves on our professionalism and aim to provide our customers with the highest level of service. To this end, all Omega people who design or report on systems installed to BS EN 62305 have undergone extensive training to ensure that we offer the optimum lightning protection solution for your needs whilst complying with all legislative requirements.

The Main Considerations

BS EN 62305 considers four separate risks:-

  • R1 – risk of loss of human life
  • R2 – risk of loss of services to the public
  • R3 – risk of loss of cultural heritage
  • R4 – risk of loss of economic value

When considering the risk assessment it is important to remember that the EN version of the standard is not identical to the BS version. The BS version includes several National Appendices, namely "NB - Assessment of probability Px of damage for a structure", "NC - Assessment of amount of loss Lx in a structure", "NH - Case study for structures", and "NK - Values determined at national level where permitted". It is important that the National Appendices and the values contained therein are applied for use in the UK otherwise the risk assessment outcome will not comply with BS EN 62305.

What Level of Protection Is Required?

The risk assessment determines which, if any, of four levels of protection are required and these form the basis for the design which, in simple terms, is applied using the configurations shown in the following table:-

Table (has long desc)

Separation distance needs to be considered in order to prevent dangerous sparking in the event of a strike. This is a rigorous exercise and is materially influenced by the class of protection and the type of earthing arrangement used.

Type of Classification

There are two classifications of earth termination in the new standard:-

Type "A" – based on individual vertically driven electrodes. Dimensions vary according to the class of lightning protection and the resistivity of the soil. This type of earth termination is suitable for structures up to 20 metres high and with non-extensive electronic contents.

Type "B" – This is typically a ring earth electrode. It should be used where the structure houses extensive electronic contents, where the contents are hazardous and/or explosive, where structures are over 20m in height, and for all non-conducting structures.

Type I equipotential bonding surge protection devices are required for all incoming services, including cables entering the structure from externally-sited building services that do not fall within a zone of protection. Where services externally fall within zones of protection, those services feeding back into the structure require Type II over-voltage surge protection devices.

Lightning Protection, A Part of BS EN 62305

A new concept within BS EN 62305 is that of internal lightning protection. This has been included in order to prevent dangerous sparking between the lightning protection system and other conductive building services in the event of a strike. Dangerous sparking is prevented by ensuring that conductive services are outside of the calculated "separation distance" or by direct bonding.

BS EN 62305 requires that practitioners are competent, and states that in order to become a specialised designer or installer of lightning protection systems a thorough knowledge of the relevant standards and several years of experience is required.

Our UK trade association, ATLAS, has delivered a comprehensive programme of training to its members, and Omega has augmented this training in order to derive a detailed working knowledge of the standard. ATLAS will undertake third party accreditation of trainees' understanding and knowledge of the standard and their competence to apply it. Ensure your contractor is competent - ask for their third party accreditation.


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