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Surging ahead

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The growing sophistication of today’s electronic equipment calls for more stringent safety measures. Helen Johnson, technical sales director, Surge Protection Devices Ltd, discusses the levels of lighting and surge protection required in order to meet the new British and European Standard, BS EN 62305. 

Recently introduced standards put equal importance on protecting the electrical installation and electrical equipment as well as the building itself. 

As technology increases, consumer’s demand that the electrical items we use get smaller, which means the components inside are also smaller. The reduction in the size of these components over the years now makes electronic equipment very sensitive to over-voltages.

An over-voltage, or a surge as they are generally called, are short spikes in voltage, which unknown to most people are occurring all the time. As the components inside the electrical equipment we use are so small, they are slowly degraded by these surges, which gradually shorten the lifespan of the equipment. 

This phenomenon affects everything that is plugged into power, from your household electronics through to industrial machinery and computers. Many computer systems are now networked and rely on each other to operate. Therefore, if one part of the system gets damaged due to lightning or surges, the whole system will not operate. The consequential losses suffered during such events i.e. downtime and lost production, can be very high.

A Type 1+2+3 combined lightning and surge device must be installed if the building is fed by over-head lines, or it has an external lightning protection system. When lightning hits the external lightning protection system (or over-head power lines) the lightning travels down the cable to the main incomer of the building. 

Although the external lightning protection system is earthed, only 50% of the total voltage from a lightning strike will go to earth, the other 50% (possibly up to 100kA) will travel across the cross-bond on to the incoming panel and out onto the electrical circuits in the installation. This creates a massive risk to the property and to any life inside. 

The Type 1+2+3 combined lightning and surge device is usually fitted in a separate enclosure and mounted next to the main board. They are wired in parallel to the supply, and can either be fed directly from an existing breaker in the board, or you can install connection blocks off the main board and wire the device into these connection blocks. 

If the building has sub-distribution boards more than 10 metres away from the incoming panel, these boards will require additional protection. A Type 2 device is usually sufficient here, unless the panels/sub-distribution boards feed external circuits such as car park lighting, CCTV etc. then these should have a combined Type 1+2+3 device fitted as standard.

In all other installations, where the building does not have an external lightning protection system and is fed by underground cable, then a Type 2 surge arrester is sufficient. This Type 2 device can sit on the main board, where it will protect all outgoing circuits. If there are any sub-distribution boards 10 metres away from the main board, then these will also need protecting with a Type 2 device. The reason for this is because surges can occur from anywhere in a building. Usually we think about the surges coming in from the mains, but generally this is not the case. Only about 20% of surges occur from outside the building. Whereas 80% of surges are generated from within the building, due to things like switching events.  

Domestic installations

Under the 18th Edition guidelines, as of January 2019, surge protection has been a requirement. This is because the surges that have always occurred in our systems now pose a threat due to the increasing use of more sophisticated electrical equipment. 

As you can imagine, the equipment we use every day is getting more technical, but also smaller. Which means that the components inside are getting smaller, so more susceptible to damage from any over-voltage. The 18th edition states the only instance surge protection may not be installed in a domestic situation is if the value of the surge protection device exceeds the value of the electrical installation, or a risk assessment has been carried out to prove the property does not require protection. 

Main incoming position 

Most modern and the latest designed Type 1+2+3 combined lightning and surge arresters will have common and differential mode protection (all mode arresters). This means that these new devices protect not only from phase to earth and neutral to earth, but also phase to neutral and phase to phase. The advantage of an all mode arrester is a very low let through voltage between all conductors, less than 600V. A device of this type will be able to handle direct lightning currents as well as protect sensitive electronic equipment from damages up to 10 metres away.

Sub-distribution boards

Type 2 devices, commonly referred to as surge arresters, are generally fitted at the sub-distribution board position. They take out of the system internal surges from switching events, which can damage sensitive electronic equipment. Any sub-distribution board more then 10 metres away from the arrester at the main incoming position should have a Type 2 device fitted. They have visual indication of status and should be checked regularly to see if they remain active. 

Final circuits

Type 3 arresters are generally fitted to stand alone pieces of end equipment fed from sockets, but not exclusively e.g. a fire alarm panel more than 10 metres away from a sub-distribution board, which has a Type 2 surge protection device fitted.


As can be seen from the above, the number of applications and the technical requirements for surge protection devices are scaling up, in order to keep pace with our demand for better, faster, ever-shrinking technology. 

If you are unsure of what is required, it is worth remembering that these standards have been revised for one very important reason; safety. It is our combined responsibility to educate ourselves and others, ensuring we continually set the (correct) standard if we are to remain protected. 

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