Transient Overvoltage Protection
18th Edition: Bulletin
The 18th Edition of the Wiring Regulations came into effect on the 1st January 2019. Several key changes have been made with regards to surge protection that may affect installers such as yourself. Here we highlight a few of those key changes.
What Are Electrical Surges?
Electrical surges are also known as transient overvoltages and can affect power, signal and telecommunications systems by overloading components, leading to failure. Surges arise from lightning or from the switching of large electrical loads connected elsewhere on the network. Lightning strikes are the source of the largest overvoltages, whether direct or up to a kilometre away from the structure. In electrical installations, lightning surges can reach 6,000V and last less than a millisecond. While switching transients are much smaller, they are more frequent and can be a source of constant stress for electronic components, leading to tripping of RCDs, unplanned outages and premature failure. The result of either type of surge is the “four Ds” of disruption, degradation, damage and downtime. Ultimately, the cost to business from these is lost productivity, staff overtime, product spoilage and delays.
Changes to the 18th Edition
Surge protection is covered in Chapter 44 of the IET Wiring Regulations (BS 7671) and the 18th Edition will contain some important changes. Contractors will need to install SPDs to protect against transient overvoltages in situations where there may be serious consequences. These are listed as loss of life or serious injury, interruption to public services, interruption of commercial activity, damage to cultural heritage, or impact on sites with large numbers of people. At all other sites (apart from single dwellings in some situations) a simplified risk assessment will determine the need for SPDs. Unsurprisingly, the requirements are greater for high risk sites such as nuclear or chemical facilities. These require a full risk assessment, as detailed in the BS EN 62305 standard for protection against lightning.
How should electrical contractors change their approach to SPDs?
The incoming regulations mean that Surge Protection Devices (SPDs) will be required for many installations in commercial, public, industrial and housing schemes. It is important to use SPDs that meet the latest safety and technical standards to ensure that they will offer the right level of protection against repeated “worst case” overvoltages. There are three Types of power SPD on the market (Types 1, 2 and 3), each of which can handle different types of surge current. Type 1 SPDs are designed for installation at a facility’s service entrance. They are also known as equipotential bonding SPDs and are designed to protect against major surges that arise from a direct lightning strike. Without a Type 1 SPD, transient overvoltages can exceed the impulse ratings of equipment or cable insulation and this can lead to dangerous sparking – therefore Type 1 SPDs protect against loss of life and serious injury. However, they do not provide protection against switching transients for sensitive electrical and electronic systems. Therefore, Type 2 and 3 SPDs are also required to protect the electrical and electronic systems. These SPDs will further reduce the size of transient overvoltages to safe levels, with Type 2 SPDs providing protection for fixed equipment and Type 3 SPDs being designed to protect sensitive or critical loads, particularly from switching transients.
Together, the three Types form a co-ordinated SPD set but it’s worth being aware that there are also Combined Type SPDs. These combine multiple Types in a single unit (for example Type 1+2+3), which can simplify installation and maintenance and save cost.
The many options for SPDs by type and application can make selecting the right products seem daunting – so we have published full guidance on our website at www.remora.net to cover SPDs for power, signal and telecoms.