BS EN 62305:2006
Here in the UK Lightning Protection Systems are designed and installed in accordance with BS EN 62305:2006 ‘Protection Against Lightning’.
The origins of this standard are derived from IEC 62305 which was issued in 2006 by the International Electrotechnical Commission (IEC). This standard IEC 62305 was adopted in its entirety as a European standard by the European Committee for Electrotechnical Standardization (CENELEC) and published in 2006 as EN 62305.
BS EN 62305:2006 is the UK implementation of EN 62305:2006, containing certain authorised National Amendments based on conditions within the UK.
The previous design standard for the UK was BS 6651:1999 ‘Protection of Structures Against Lightning’, however following a two year introductory period where BS EN 62305 ran in parallel, BS 6651:1999 was withdrawn at the end of August 2008.
BS EN 62305:2006 ‘Protection Against Lightning’ comprises of four parts each covering a particular element, these are as follows:
BS EN 62305 — Part 1: General Principles
This opening part of the standard introduces the technical theory behind the protection measures detailed in the three other parts and gives a general overview of the concept behind the design of a Lightning Protection System.
BS EN 62305 — Part 2: Risk Management
The nucleus of the standard is the ‘Risk Assessment’ and this is key to the correct implementation of parts 3 and 4.
Although this calculation is very complex and requires many different ‘weighting factors’ the advantage is the appropriate level of protection is applied to the structure. There are four protection levels to choose from, these are covered in more detail in Part 3.
The following types of loss may result from damage due to lightning and each should be considered, relevant to the structure to be protected:
- L1 / R1 — Loss of human life
- L2 / R2 — Loss of service to the public
- L3 / R3 — Loss of cultural heritage
- L4 / R4 — Loss of economic value
BS EN 62305 — Part 3: Physical Damage to Structures and Life Hazard
This part of the standard details the protection measures required, in and around a structure, to protect against physical damage and injury to living beings.
A lightning protection system is made up of three main components, as follows;
Air Termination Network:
The primary function of the air termination network is to capture the lightning discharge. The lightning current is then dissipated to earth via the down conductors and earth termination system.
The designer can choose from three basic methods (or a combination of these) to determine the extent and position of the air termination network, these are;
- rolling sphere
- meshed conductor network
- protective angle
There are different sizes, spacings and angles of the above to suit each level of lightning protection.
Down Conductors:
The quantity of down conductors required is dependant upon the size of the structure and directly linked to the perimeter measurement.
The spacing of the down conductors around the structure is determined by lightning protection level (LPL), but vary between a typical distance of 10m for a level 1 system (highest level) and 20m for a level 4 system (lowest level).
Where ever possible it is encouraged to utilise natural components such as structural steel columns or reinforcing bars within concrete columns as the down conducting elements.
Earth Termination System:
The earth termination system is the part of the installation installed within the ground and its correct design is vital for the dispersion of the lightning current safely to earth.
A combined overall resistance of 10 Ohms or lower must be achieved and at each individual position the maximum value should not exceed 10 times the total number of earth positions within the system. For example if a structure has a total of 8 No, earth positions the resistance value at each position should not exceed 80 Ohms (8 positions x 10 Ohms = 80 Ohms).
There are two basic options for the earth termination system given within BS EN 62305:2006, these are as follows:
Type A Arrangement
This consists of either horizontal or vertical earth electrodes driven into the ground and connected to each down conductor. This arrangement is suitable for low structures (below 20m), existing structures or when there are non-extensive electronic systems within the structure.
Type B Arrangement
A Type B arrangement comprises either an earth ring conductor buried in the ground around the perimeter of the structure (at least 80 % of its total length should be contact with ground) or a foundation earth electrode, such as a pile foundation.
This arrangement is recommended and preferable for new build structures or when the structure is either located on bare solid rock, incorporates extensive electronic equipment or represents a high risk of fire.
BS EN 62305 — Part 4: Electrical and Electronic Systems within Structures
One of the most significant factors of BS EN 62305:2006 is the requirement for the protection of electrical / electronic systems within the structure to be considered as an integral part of the lightning protection system.
Within this part information is provided for the design, installation, maintenance and testing of a Lightning Electromagnetic Impulse (LEMP) protection measures system (LPMS) for electrical / electronic systems within a structure.
The term LEMP simply defines the overall electromagnetic effects of lightning that include conducted charges (both transient overvoltages and transient currents) as well as radiated electromagnetic field effects.
An LPMS is defined as a complete system of protection measures for internal systems against LEMP.
Failure of internal systems due to Lightning Electromagnetic Impulse (LEMP) is possible from all points of strike to the structure or service (both direct or nearby).
Protection of electronic systems from transient overvoltages can prevent:
- Lost or destroyed data
- Equipment damage
- Repair work for remote and unmanned stations
- Loss of production
- Health and safety hazards caused by plant instability, after loss of control.
- Loss of life — protection of hospital equipment
