Most modern businesses heavily rely on Telecoms, it and other electronic systems - take them away and many companies would struggle to function. The new British Standard, BS EN 62305 Protection against lightning, makes a welcome step forward by introducing procedures that will give a much greater level of protection against an electrical surge. UK contractors need greater awareness of the requirements of this new Standard, says Andy Malinski, technical director at Omega Red Group
The damage and degradation caused by transient over-voltages to electrical systems have long been understood by electrical engineers in Europe and elsewhere. In the UK, high voltage (HV) surge arrestors are installed as standard components in the electricity supply infrastructure, fitted to avoid costly network downtime, but there still appears to be a strong reluctance to fit surge protection devices (SPD) to the low voltage (LV) networks used in commercial and domestic environments.
With only an advisory appendix for surge protection in the previous British Standard the reasons for this reluctance probably have more to do with an ingrained resistance to change rather than any hostility to the new standard. Surge protection is included for reasons of good working practice rather than some unnecessary bureaucratic standardisation with our European neighbours.
As before, the new Standard covers the need to provide structural protection but it now also addresses the need to offer protection to electrical and electronic systems against lightning currents and transient over-voltages.
Since the new Standard was introduced in September 2008 the construction industry should have noticed a change in response from contractors to their enquiries about lightning protection systems. Surge protection devices (SPDs) form an integral part of BS EN 62305 and need to be installed for a fully compliant lightning protection installation.
Additionally there are now four different protection levels which can be applied for structural lightning protection. The level of protection is dependent on the outcome of a risk assessment which is far more complex than the outgoing standard and has many new factors to consider including building services, occupancy hours and number of people to list a few. For the UK construction industry this involves a steep learning curve. In any event, service entry SPDs will be required on all four structural protection levels for compliance.
In real terms why do we need SPDs and what should we all be doing about them? The answer is very simple. If the cables entering a structure have been exposed to lightning, either via a direct strike or by induction, then the conductive cores of the cable may carry dangerously high voltages in to the structure leading to sparking at the termination points due to the break down in the insulation of the cables or equipment.
This theory is not only being applied to the service entry points, which is a minimum requirement, but also to any exposed plant or other electrical/electronic units being fitted to the structure. Plant items on the roof (AHU etc), a control system for electric gates, car park lighting, CCTV systems may all include copper cables entering or leaving buildings.
There are three ways in which transient voltages can be introduced into a structure via copper cables:
A cloud to ground lightning strike injects a massive current into the ground raising the ground potential in the area of impact to a high level and for the current to dissipate it will seek the path of least resistance to earth. Cables running between buildings are usually connected to different earthing systems at each end and a cable connected to an earth of a lower value forms an ideal route for the induced current to follow.
A lightning discharge causes a huge current to flow; this in turn sets up a massive magnetic field. Any conductor passing through this magnetic field will have a surge voltage induced on the cable; this is the same principle on which a transformer operates.
Atmospheric disturbances cause high voltages to be generated. A low voltage conductor in the area of influence of these voltages can be charged to that same voltage, this has the same effect as charging a capacitor.
Any cable entering or leaving a structure may carry back a problem but the installation of SPDs at the nearest point of entry or exit will reduce the effect of a surge. It is important to note that the service entry or equipotential Bonding SPDs are designed to handle a 10/350µs current and are commonly referred to as lightning current SPDs.
The purpose of these frontal surge protection devices is to divert partial lightning current away to earth and limit the let-through voltage to a safe level in order to prevent dangerous sparking. A competent installation company, with appropriately trained staff, should be able to advise the contractor on the best units to use - it is vital to check they comply with BS EN 62305-4 and IEC 61643.
You may be wondering why, after all these years under the previous British Standard, do we need to be looking at surge protection? The answer in very simple terms is progression; outside of the UK and especially within Europe, surge protection has been a common part of lightning protection installations for many years and the value of surge protection is well established.
BS EN 62305 has incorporated guidance and Standards employed within the UK, Germany, France and many other countries, taking available technology and applying it across the industry, just as we have with other Standards and systems in the past. The Germans have a simplified method of SPD selection which is based mainly on the use of the building to be protected and is endorsed by German insurance companies. This has evolved after many years experience and incidence recording and could well be replicated within the UK in years to come.
Under BS EN 62305 SPDs are now an integral part of lightning protection designs. It is also important to remember the certification of a system; failure to provide the entry surge protection units will mean a non-compliance with the Standard. Engineers need to understand a new system installed to BS EN 62305 should have service entry surge protection fitted as a minimum. These units should be compliant with the Standard's requirements or they may fail in the task they have been designed to carry out.
Omega Red Group has invested a great deal of time and effort in training for the design and installation of SPDs and lightning protection systems. Of course, any contractor would expect its chosen installer to know what they are talking about but a sound grasp of the requirements of the new standard is necessary to identify whether that is the case. Our engineers will always be happy to answer any questions you might have but a good starting point for understanding the basic principles of BS EN 62305, especially the SPD components, can be found in a short webcast tutorial at http://www.omegaredgroup.com/