Although an amendment to the IET Wiring Regulations issued in 2011 placed an increased emphasis on surge protection, a huge number of electrical installations in the UK still have no surge protection. Is this omission justified or is it a risk too far? Peter Croucher, product manager at Weidmuller, investigates


urge protection? Why bother? “We don’t get much lightning in these

parts!” It’s a common enough sentiment and, at first sight, it may even seem to be quite reasonable. But in truth this sentiment is based on a number of major misconceptions, and can have serious and costly consequences. Probably the most significant

misconception is that surge protection is all about protecting equipment, installations and ultimately people from the effects of lightning. It isn’t. A surge is a very short duration overvoltage on the mains supply, lasting a few microseconds at most. Even though the surge lasts for such a short time, its magnitude can be high enough to damage electrical and electronic equipment. It is true that lightning strikes in the vicinity of power lines produce such surges, but they are not the only source and they are not even the most common source. Voltage surges on the mains supply are more frequently caused by switching operations, such as the starting or stopping of a large motor, or when the local utility company needs to reconfigure the power distribution network to, for example, bypass a fault. It’s clear then, that “we don’t get much

lightning here” is not a sound basis for deciding whether to install surge

protection, and even if it were, the belief that lightning is rare in the UK is not well founded. According to the Tornado and Storm Research Organisation, in an average year, the UK, Ireland and surrounding seas, experience between 200,000 and 300,000 lightning strikes. If you’re running a business that

depends heavily on its electronic infrastructure then voltage surges do matter. It is this type of equipment surges that are most likely to damage or even destroy. The resulting disruption can be costly and, in extreme cases, can even lead to a business going bankrupt. There is another aspect to consider.

Many people believe that they have no need of surge protection because they’ve never had it, and nothing bad has ever happened as a result. This is a bit like saying that you don’t need theft insurance for your home because you’ve never had a burglary. You could always be lucky, of course, but you only need to be unlucky once and the consequences could be dire. A good way to look at surge protection is, in fact, to consider it to be a form of insurance where the premium – the cost of installation – is relatively small, and in most cases will only need to be paid once. The next step is to consider what form of surge protection you should install.


There’s plenty of guidance available on this topic on the Weidmuller website, the British Standard, BS EN 62305 - Protection against lightning, and in the IET Wiring Regulations. The key point, however, is that an effective surge protection installation is a system, not just a single device. Surge protectors are divided into three classes. Class 1 devices are installed at the main distribution board, and are required when an external lightning protection system, or overhead lines are installed. They absorb a lot of energy, but allow a comparatively high voltage rise. Class 2 devices are installed directly after a Class 1 device and at sub-distribution boards. They are capable of absorbing less energy, but they also limit the voltage rise to a lower level. Class 3 devices are fitted close to sensitive equipment like PLCs and provide even more effective voltage limiting. Many installations will include surge protectors from all three classes, but this is not always necessary. What is necessary, however, is dependable expert advice on choosing and installing the right surge protection solution for a particular application. Hopefully, this article has presented

convincing arguments for installing surge protection. If you’re the owner or manager of an organisation, these arguments apply directly to you. If you’re an electrical contractor, they are arguments you may well want to put in front of your clients.

Weidmuller T: 01162 821261


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