What you need to know about surge protection devices (SPDs)

Surge protection devices (SPDs) help to prevent excess voltage from damaging electronic devices, equipment or systems during a short surge of electricity known as a transient over-voltage.

Transient over-voltages are electrical surges or spikes of sometimes several thousand volts which last no more than a millisecond in duration. They can be caused externally by an atmospheric event such as a lightning bolt or internally when electrical switching occurs. Internal surges account for around 65% of transient over-voltages.

These electrical surges can cause damage or destruction of electronic items such as computers and microwaves, or electrical installations or systems such as fire or security alarms. They can have a huge impact on businesses, services and organisations due to the loss of data, the malfunctioning of vital electronic equipment, operational downtime, and an increased risk of fire.

During an electrical surge, SPDs provide protection by limiting transient voltages and diverting excess voltage into the Earth current or back to its source. Particularly in installations where continuous usage is essential, it’s vitally important to ensure electrical systems are safeguarded by SPDs at various points within an electrical system.

Assessing the need for SPDs

The latest (18th) Edition of the IET Wiring Regulations – otherwise known as BS 7671 – came into force at the beginning of this year and contains revised sections regarding transient over-voltages and the installation of SPDs. The regulations require all new electrical systems, installations, alterations and additions to undergo an assessment to establish the risk of transient over-voltages and which kind of SPDs, if any, should be installed to ensure protection.

The redrafted Chapter 44 states that protection must be provided where over-voltage could cause serious injury or death, interruption or damage to public services or cultural heritage buildings, disturbance to commercial or industrial activity, or an impact on a large group of people within the same area. In all other installations, a risk assessment must be carried out to determine if protection against transient overvoltage is required.

Section 443 defines how to assess the risk of transient over-voltages. Factors to consider include the level of exposure of a building to lightning or the likelihood of transient over-voltage occurring within an electrical installation.

A full BS EN 62305-2 assessment is required for high risk sites such as nuclear or chemical plants where a power surge could cause an explosion or the release of harmful emissions. For structures at risk of lightning strikes, SPDs should be installed in accordance with BS EN 62305.

Which type of SPD to choose?

Section 534 of the IET Regulations details the requirements for the selection and installation of SPDs.

There are two main types of SPDs, voltage limiting and voltage switching, but many devices now incorporate both components to provide the best possible protection. There are a range of SPDs available so it’s important to work with an expert to ensure the correct type of SPD is chosen for the requirements, and to ensure it meets regulations.

The selection of an SPD should be based on a number of considerations, including the value or sensitivity of the equipment being protected, the risk of a lightning strike of transient over-voltage, and the location of the SPD and level of protection it can provide. There are three different types of SPD which each provide different protection. Type 1 can divert lightning surges; Type 2 prevents the excess voltage from spreading within an electrical installation and protects equipment connected to it; Type 3 provides additional protection when there are sensitive loads. Combined type SPDs can also be installed.

How DRF Electrical can help

As experienced electrical contractors, the DRF Electrical team has been fitting SPDs for many years to ensure electronic equipment and electrical installations are safe and conform to regulations and best practice. We can undertake risk assessments to establish SPD requirements, as well as carrying out the installation, maintenance and testing of SPDs to ensure all installations adhere to the 18th Edition of the IET Wiring Regulations. To find out more about surge protection devices and how to choose the correct one for your requirements, call us on 0113 257 8212.

If you found this article useful, maybe you’d like to read our blog Everything you need to know about arc fault detection devices (AFDDs).