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Do you know how much you are at risk?

01 June 2012

Stuart Jaycocks takes a look at BS EN 62305, a new standard that provides very broad and comprehensive coverage of surge protection relating to modern electronic systems and much more besides.

The most familiar source of a power surge is lightning, though it is in fact one of the least common causes. More commonly, power surges occur during the operation of high-power electrical devices, such as elevators, air conditioners and refrigerators, the switching of which creates sudden, brief demands for power that can disrupt the supply system voltage. While these surges are nowhere near the intensity of a lightning surge, they can be severe enough to damage equipment components.

Other sources of power surges include faulty wiring, problems with a utility company's equipment, and damaged power lines. The system of transformers and lines that brings electricity from a power generator to the outlets in our homes, offices and factories is extremely complex. There are dozens of possible points of failure, and many possible errors that can cause an uneven power flow.

The BS EN 62305 standard was introduced with a vast amount of detail on how to choose the correct surge protection device for a particular application. Because risk assessment is now a far more comprehensive and laborious task, the volume of the documentation grew massively from that which accompanied the previous BS 6651 standard.

BS6651 only dealt with the protection of the physical structure and was written in 1985 by a UK technical committee. BS EN 6230, written by the Geneva based International Electrotechnical Commission, on the other hand, includes risk management. This covers the risk of loss of human life, loss of service to the public, loss of cultural heritage and economic loss. It is the result of many years of collaboration between hundreds of lightning protection experts from 28 different countries, and while it may be a difficult and expansive document to get to grips with, it is nonetheless crucial for the surge protection sector.

Lightning risk assessment
The biggest challenge operatives face today is the practical application of lightning risk assessment, because it requires considerable additional information to ensure that the entire building is adequately protected. This includes not only the structure but also the services, telecommunications and the incoming power lines. Given our reliance on digital services today, this is no small task.

Risk assessors need to consider factors such as the overall dimensions of the building structure, its uses and the type of equipment installed both inside and out. Understanding the composition of floor surfaces and the location of power and telecommunications cables - and their proximity to other structures - are also key considerations, as is, of course, fire protection.

It is reported that the UK receives around one million lightning strikes every decade. Yet, despite these apparent dangers and the critical nature – and vulnerability - of many business systems, the continued high numbers of insurance claims for lightning damage suggests that many organisations are not taking adequate lightning protection measures.

Especially at risk are free-standing areas of plant sited away from a main building; fuel storage or water treatment control systems and telemetry installations are good examples. Solar and wind power plants are also vulnerable.

A surge or voltage spike of sufficient magnitude can cause serious damage to equipment and associated cabling. And even if a surge doesn't immediately cause the equipment to fail, it may put extra strain on its components, accelerating wear and reducing its life.

Surge protection – the technology
Surge protectors can assist in preventing this from happening. A surge protector (or surge suppressor) is a device that will protect electrical systems from voltage spikes by either blocking or by shorting to ground voltages above a safe threshold.

A standard surge protector passes the electrical current along from the outlet to a number of electrical and electronic devices plugged into the power strip. If the voltage from the outlet surges or spikes, the surge protector diverts it to ground. In the most common type of surge protector, a component called a metal oxide varistor (MOV) acts as the diverter, forming a connection between the hot power line and the grounding line.

If voltage in a circuit is too high, the MOV is capable of conducting sufficient current to limit the surge. As soon as the extra current is diverted via the MOV to ground, the voltage in the hot line returns to normal, and the MOV resistance is restored. In this way, the MOV only diverts the surge current, while enabling the normal operating current supply to equipment connected to the surge protector.

BS EN 62305 Protection against Lightning comprises four parts: Part 1 - General Principles; Part 2 - Risk Management, which defines the level of lightning protection system required, based on a risk assessment; Part 3 - relating to physical damage to structures and life hazards; and Part 4 covering the protection of electrical and electronic systems housed within structures.

When embarking on a surge protection programme, a business should begin by assessing how much it is at risk by the types of loss that it could incur, should it be struck by lightning or a power surge. There are four types of loss defined in BS EN 62305: loss of human life, loss of service to the public, loss of cultural heritage (historic buildings, monuments, etc) and loss of economic value. This last type considers the cost of the physical loss of the equipment, but not the consequential losses as a result of downtime.

In making this assessment, it is important to remember that there are two types of lightning strikes – direct and remote. Direct or close strikes are those into the lightning protection system of a building, in close proximity to it, or into the electrically conductive systems implemented in the building, such as the low-voltage supply, telecommunications or control lines. Remote lightning strikes are those that occur at a distance as well as lightning strikes into the medium voltage overhead system or in close proximity to it, or lightning discharge from cloud to cloud.

Once the risk is assessed, it is then necessary to look up in the table in the National Annexes, the tolerable risk for these types of losses. The standard provides the means of calculating the actual risk. Logically, if the actual risk is higher than the tolerable risk, then the protection requirements are set out in the tables in the standard.

Part 3 of the standard defines four levels of lightning protection based on possible minimum and maximum lightning currents, which relate to classes of lightning protection systems. These are used to define several attributes of the lightning protection systems. The standard also recommends a single integrated termination system for a structure and provides detailed explanations of the reasons for equipotential bonding. It explains the choice of lightning protection system components and conductors with various tables relating to sizes and types of conductor and earth electrodes.

The final part of the standard, Part 4, has arisen as a result of the increasing cost of failures of electrical and electronic systems, caused by electromagnetic effects of lightning. It provides information on protection measures to reduce the risk of permanent failures of electrical and electronic systems within structures.
Part 4 also covers the design, installation, inspection, maintenance and testing of a lightning electromagnetic impulse protection system for electrical and electronic systems within a structure. And finally, there’s guidance on how to reduce the risk of permanent failures due to lightning electromagnetic impulse.

The scope and diversity of surge protection devices can be as complex as the new standard itself, from lightning arresters, high power varistors and surge monitoring modules, to data interfaces and surge protection for photovoltaic systems. With this clear definition from BS EN 62305, you no longer need to be at risk.

Stuart Jaycocks is with Weidmuller


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