The 18th Edition of the wiring regulations B.S.7671 20018, recommends that surge protection devices (SPDs) are installed for protection against transient overvoltage.
What is transient overvoltage and why do I need protection?
The twenty first century has seen a huge increase in computerised equipment, permanently, or constantly connected to the electrical supply in our buildings.
We have semi-intelligent equipment like Alexa, Google dot and such like, smart phones and tablets, laptops, desktops and networks constantly connected to the power supply.
We have sensitive microchips in LED lighting, heating and ventilation controllers and automated lighting systems. Even domestic appliances like washing machines are often controlled by small circuit boards and chips.
All these are sensitive to large spikes in voltage, such voltage spikes can seriously damage or even “fry” the circuit boards. This could be expensive, for example, if 100 LED light fittings and 30 computers are damaged as a result.
So, what causes these spikes or transient overvoltage?
Well, the biggest cause is lightning strikes. Fortunately, in this country, we do not see as many as they do in some parts of Europe.
However, some areas such as the East Midlands, Lincolnshire and Suffolk are more heavily affected than other parts of Great Britain. A lightning strike will send a massive voltage to ground, which will dissipate across the ground. Some voltage can also be picked up and travel along the cables that are connected to earth and back-feed into our buildings.
Another cause of overvoltage is start-up. If there is a power cut, or if the main switch is turned off for maintenance for example, when it is re-energised, the start-up current of all the equipment connected can produce an extreme voltage spike.
Regulation 443.3 recommends that SPDs are fitted where overvoltage could:
- Result in serious injury to, or loss of, human life, or
- Result in interruption of public services and/or damage to cultural heritage, or
- Result in interruption of commercial or industrial activity, or
- Affect many co-located individuals.
For all other cases, a risk assessment shall be performed.
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