BSEN 62305 Overview
The current British Standard for Protection Against Lightning is, BSEN 62305 2011. This is a complex document derived from the International Electrotechnical Commission document EN62305 which was adopted in its entirety by the European Committee for Electrotechnical Standardization (CENELEC) and is categorised in four parts.
- Part One - General Principles
- Part Two – Risk Management
- Part Three - Physical damage to structures and life hazard
- Part Four - Electrical and electronic systems within structures
The main differences between this and the previous British Standard (BS6651) was the introduction of a complex risk analysis calculation to establish which of four levels of protection should be applied to a particular structure, and emphasis on protection from the secondary effects of lightning by providing surge protection devices, (SPDs), to services entering and leaving the structure.
Levels, or Classes of protection, range from 1 to 4 and are dependent on a number of factors, the major contributors being the actual physical size of the structure to be protected, its occupants and usage.
Level 1 is the most stringent through to level 4 being the least in terms of the amount of physical protection actually required.
In addition to structural protection, all services entering or leaving a structure and from any roof mounted equipment, must be provided with suitable surge protection devices (SPDs). This typically involves the main supply, telephone and data cables, cctv, pv arrays and external lighting, signage or remote structures fed separately from the main distribution board.
It is therefore recognised that danger exists not only from a direct strike to a structure from a lightning discharge of up to 200KA, but indirect strikes causing havoc to our internal electrical equipment costing thousands in unnecessary and avoidable loss of production and insurance claims.
The standard is based on four principle risks and providing protection to reduce the appropriate risk to below a tolerable level.
Those risks are defined as follows.
- R1 – Loss of human life
- R2 – Loss of service to the public
- R3 – Loss of cultural heritage
- R4 – Loss of economic value
In the vast number of cases, the only two risks which are realistically applied are R1 and R2. Generally speaking any structure which is occupied, at any time, is subject to risk R1, loss of human life. Structures such as hospitals, emergency services, data centres, education, military and government establishments for example would, in addition to R1, be considered under the R2 risk category, loss of service to the public.