Expanding on an article in the May issue of Electrical Review John Sherlock of Furse pictured right , offers an overview of the new standard and the consolation that, complex as the new standard may be, its key concepts are not alien, and, with relevant technical advice and support, it can be mastered BS EN came into force on 1 September At the moment, it runs concurrently with BS , but ultimately BS will be withdrawn and BS EN will be the only recognised standard by the end of August The new standard consists of four parts: BS EN : Part 1 General principles This is an introduction to the other parts of the standard. It includes many more parameters than BS which devotes 9 pages including figures, whilst BS EN contains some pages. BS EN contains a series of National Annexes, from which individual countries, like the UK, have used their own interpretation and perception of risk to compile parameters for certain elements of the risk assessment. The first stage of the risk assessment is to identify the types of loss that a structure and its contents can incur.
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Expanding on an article in the May issue of Electrical Review John Sherlock of Furse pictured right , offers an overview of the new standard and the consolation that, complex as the new standard may be, its key concepts are not alien, and, with relevant technical advice and support, it can be mastered BS EN came into force on 1 September At the moment, it runs concurrently with BS , but ultimately BS will be withdrawn and BS EN will be the only recognised standard by the end of August The new standard consists of four parts: BS EN : Part 1 General principles This is an introduction to the other parts of the standard.
It includes many more parameters than BS which devotes 9 pages including figures, whilst BS EN contains some pages. BS EN contains a series of National Annexes, from which individual countries, like the UK, have used their own interpretation and perception of risk to compile parameters for certain elements of the risk assessment.
The first stage of the risk assessment is to identify the types of loss that a structure and its contents can incur. These risks are: l R1 — loss of human life l R2 — loss of service to the public l R3 — loss of cultural heritage ie. It does not, however, take into account the economic value of consequential losses from system downtime. Once the applicable types of loss have been identified, a tolerable risk RT for each can be looked up in a table contained in the National Annexes.
The actual risk R is then arrived at through a series of calculations, using formulae in the standard and including various weighting factors. If the actual risk R is lower than the tolerable risk RT , then no protection measures are needed. If R is greater than RT, then protection measures, as determined from the tables given in the standard, are required.
A series of trial and error calculations is then required in order that a sufficient level of lightning protection can be defined. BS EN : Part 3 Physical damage to structures and life hazards The third part of the new standard relates directly to the main body of BS , but there are significant differences between the two. In BS , a mesh arrangement was the commonly used layout for the air termination network.
However, BS EN details the use of air rods or finials, catenary or suspended conductors or a meshed conductor network, in any combination. The new standard also includes three methods for determining the position of the air termination system: l The rolling sphere method whose radius also depends on the class of LPS l The protective angle method a mathematical simplification of the rolling sphere method l The mesh method As with BS , the new standard recommends a single integrated earth termination system for a structure.
In BS a system was used where each down conductor was attached to an earth electrode. BS EN contains extensive sections, with detailed explanations on the reasons for, and methodology of, equipotential bonding.
It requires the bonding of all metallic services to the main equipotential bonding bar. BS recommends the inspection of any LPS annually. BS EN goes further, categorising inspection into visual inspection, complete inspection and critical systems complete inspection, whose frequency depends on the LPL in force.
BS EN : Part 4 Electrical and electronic systems within structures This part contains one of the most critical differences between the two standards. In BS , the protection of electronic equipment is only included in an informative annex.
Structural lightning protection cannot now be considered in isolation from transient overvoltage or surge protection.
From that risk assessment, a structure may need both a structural LPS and a fully co-ordinated set of surge protection devices SPDs or just overvoltage protection alone. LPZ 1 sees limited induced current and damped magnetic field whilst LPZ 2 has a further reduction of induced current and further damped magnetic field. Successive zones are therefore characterised by significant reductions in LEMP severity, achieved through a combination of protection measures such as bonding, shielding and the use of SPDs.
Protection levels within a zone must be co-ordinated with the immunity characteristics of the equipment to be protected, ie, the more sensitive the equipment, the more protected the zone required.
The existing fabric and layout of a building may make readily apparent zones, or LPZ techniques may have to be applied to create the required zones. When applying bonding, shielding and SPDs, technical excellence must be balanced with economic necessity. For new builds, bonding and screening measures can be integrally designed to form part of the complete lightning protection measures system LPMS.
However, for an existing structure, retrofitting a set of co-ordinated SPDs is likely to be the easiest and most cost-effective solution. SPDs also provide additional protection over bonding and shielding measures through protection in both common and differential modes. This ensures equipment is not only protected from damage but also remains operational during lightning activity. This simply means a series of SPDs whose locations and LEMP handling attributes are co-ordinated in such a way as to protect the equipment in their environment by reducing the LEMP effects to a safe level.
So there may be a heavy duty lightning current Type I SPD at the service entrance to handle the majority of the surge energy, plus downstream overvoltage SPDs to protect terminal equipment. Appropriate SPDs should be fitted wherever services cross from one LPZ to another Conclusion So, this brief overview of the new BS EN lightning protection standard clearly demonstrates how it is more complex and exacting than its predecessor.
However, the key principles are well established and pretty familiar to all. Moreover, established suppliers of lightning protection solutions are now offering a wealth of quality support tools. These include risk assessment software to automate the complex and repetitive risk calculations, new technical literature, training seminars and face-to-face assistance. BS EN will take some time for people to fully interpret and comprehend, but by using the resources available, the issues they may initially encounter certainly can be mastered.
BS EN IEC 62305 Lightning protection standard
This part of EN sets out all the requirements needed to protect buildings and structures against physical damage by implementing a lighting protection system LPS. It also looks at how to protect humans and animals living beings against injury if they are close to an LPS. By defining these safety measures, this standard helps you to minimise damage, invest in the right electrical protection equipment and maximise hazard prevention in buildings. Surge and climatic protection, earthing and electrical safety in general are also included at no extra cost.
BS EN 62305
These parts of the standard are introduced here. In these parts underwent periodic technical review, with updated parts 1, 3 and 4 released in Updated part 2 is currently under discussion and is expected to be published in late It differs from BS in as much that this new part has four Classes or protection levels of LPS, as opposed to the basic two ordinary and high-risk levels in BS
BS EN 62305-3:2006
BS EN 62305-3:2011
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