ISEN 62305:2011

ISEN 62305:2011 – Protection Against Lightning has superseded IS 6651:1999 Code of Practice for Protection of Structures Against Lightning. ISEN 62305:2011 is split into four sections, as detailed below. Here we will give a brief overview of the new standard.

BSEN 62305:2011 incorporates various changes from BS 6651:1999 and is significantly more comprehensive. It is split into the following four sections:

(1) General Principles – an introduction to the other parts.
(2) Risk Management – defining the level of Lightning Protection System required.
(3) Physical Damage to Structures and Life Hazard – defines four lightning protection levels.
(4) Electrical and Electronic systems within Structures – this section contains one of the most critical differences between the two standards, making the protection of electronic equipment an integral part of the standard and emphasising the use of co-ordinated surge protection devices – SPDs.

ISEN 62305:2006-1 General Principles

This is the general introduction to the remaining parts and describes how to design a lightning and surge protection system from the starting data received.

ISEN 62305:2012-2 Risk Management

BSEN 62305:2012-2 provides an extensive guide for the Risk Assessment of a proposed LPS. This document is significantly more comprehensive than the Risk Assessment criteria of BS 6651:1999.

The four separate risks that can be applied to buildings when risk assessing their Lightning Protection requirements are as follows:

  • Risk of loss of human life (R1).
  • Risk of loss of service to the public (R2).
  • Risk of loss of cultural heritage (R3).
  • Risk of loss of economic value, i.e. cost of the physical loss of equipment (R4).

The formulae detailed in this section, allows selection of required protection to reduce ‘Actual Risk’ (R) below ‘Tolerable Risk’ (RT)

It is advised in the current standard that protection may be in the form of:

  • Lightning Protection System
  • Transient Surge Protection
  • All of the above

ISEN 62305:2011-3 Physical damage & life hazard

This section details protection measures in and around a structure.

BSEN 62305:2011-3 defines four different classes of protection based on likely maximum and minimum lightning currents. These levels form the basis of the different classes of lightning protection system (LPS). The basis of the design are taken from the table below; -

Class of LPSMesh Size (m)Down Conductor Spacing (m)

There are two main types of earthing arrangements in ISEN 62305:

Type A: – Vertical earth electrodes, solid copper plates or copper lattice mats.

Type B: – Ring earth around the perimeter of the building

ISEN 62305:2011-4 Electrical & Electronic systems

This section has two major differences from that of IS 6651:1999. IS 6651:1999 provides only a brief overview of equipment protection (annex C). In ISEN 62305:2011 it is an integral part of the standard. This means that structural lightning protection cannot now be considered in isolation from surge protection or transient overvoltage.

Lightning electromagnetic impulse protection and structural protection can be determined using the risk assessment detailed in IS EN 62305:2011-2. Lightning Protection System zoning is also covered in detail in comparison to IS 6651:1999. Zoning is categorised as follows:

  • Two internal zones
  • Two external zones

The electromagnetic impulse severity can be minimised using bonding, shielding and Surge Protection Devices (SPDs).

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