Going, Ready or Not
Samad Khan, Surge Protection Product Manager for Furse, considers two of the most challenging changes to BS EN 62305:2006 Protection Against Lightning– Risk Assessment and Lightning Electromagnetic Impulse (LEMP) protection.
August 31st 2008 sees the biggest change in lighting protection standards for over 20 years, as the old BS 6651:1999 Protection Against Lightning is finally withdrawn, to be fully replaced by
BS EN 62305:2006. The new standard, introduced in 2006, is much more complicated than the old, and there are clear indications that industry professionals, comfortable with the old standard, are leaving themselves unprepared to work with the new.
Risk Assessment
BS EN 62305 Part 2 deals solely with risk assessment, which is considered in a more in-depth, technical way and includes many more parameters than in BS 6651.
Now, not only does risk assessment consider the body of the structure, but also the services, (eg. power and telecom lines), that supply it. Furthermore, BS 6651 was primarily concerned with the risk of death/injury, but the new standard has four areas of risk, considering losses of: human life, service to the public, cultural heritage and economic value.
A risk assessment must be undertaken for each of these risks, to identify whether the actual risk is below or above the tolerable risk. In the latter case, a further series of trial and error calculations have to be made to identify which combinations of protection measures will reduce the risk to an acceptable level. The results dictate the type and level of lightning protection required – structural and/or LEMP.
The new calculations are much more complex and time-consuming than those required under BS 6651. Indeed, if done longhand, the calculations for a single project can take many hours, possibly compromising a consultant’s or installer’s ability to provide accurate quotations in a reasonable time.
Lightning Electromagnetic Impulse (LEMP) protection
BS EN 62305 accepts that we now live in the electronic age, with its Part 4 making LEMP protection for electronic and electrical systems integral to the standard. LEMP is the term given to the overall electromagnetic effects of lightning, including conducted surges (transient overvoltages and currents) and radiated electromagnetic field effects. Previously surge protection was included as an advisory annex in the BS 6651 standard, with a separate risk assessment. However, the new standard’s single risk assessment dictates whether structural and/or LEMP protection is required. So structural lightning protection can not now be considered in isolation from transient overvoltage protection, known as Surge Protection Devices (SPDs) within this new standard.
Indeed, even where only a structural lightning protection system is required, BS EN 62305 requires the bonding of all metallic services to the main equipotential bonding bar, using an SPD where the services have “live” cores, such as power and telecom cables. Such SPDs are required to protect against the risk of loss of human life by preventing dangerous sparking that could present fire or electric shock hazards. Known as Type I equipotential bonding SPDs, they are also used on overhead service lines feeding the structure that are at risk from a direct strike. However, the use of these Type I SPDs alone “provides no effective protection against failure of sensitive electrical or electronic systems”, to quote BS EN 62305 part 4.
Part 4 of the new standard further emphasises the use of co-ordinated SPDs. This is a series of SPDs (Type I, II and III) whose locations and LEMP handling attributes are co-ordinated in order to protect electronic equipment. Whilst outright damage to equipment is not desirable, the need to minimize downtime as a result of loss of operation or malfunction of equipment can also be critical. This is particularly important for industries that serve the public, be they hospitals, financial institutions, manufacturing plants or commercial businesses, where the inability to provide their service due to the loss of operation of equipment would result in significant health and safety and/or financial consequences. BS EN 62305 therefore considers the use of Enhanced SPDs (SPD*) that further reduce the risk of damage and malfunction to equipment. Installers will therefore need to be much more aware of the application and installation requirements of SPDs than perhaps they may have been previously.
Here to Help
To support consultants, installers and end users needing to come to grips with the new standard, Furse has used it 100 years’ experience in lightning protection to create a range of technical support options. In addition to a bespoke, commercially available, risk assessment software and training package, Furse also offers newly revised technical literature dedicated to lightning protection under BS EN 62305, and CPD accredited seminars introducing and explaining the requirements of the new standards.
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