Surge protection devices (SPDs) are mandated under the 18th Edition of the Wiring Regulations and are essential for safeguarding equipment against damage. With the proliferation of electrical and electronic devices in modern infrastructure, the role of SPDs has become increasingly critical in ensuring the reliability and longevity of equipment. 

The Importance of Surge Protection 

Nearly every building in the UK, irrespective of its use, contains electrical devices and equipment vital for daily operations and convenience. These devices range from critical infrastructure like hospital equipment and industrial machinery to everyday items such as computers and home appliances. However, transient over-voltages, commonly known as power surges, can cause significant damage to this equipment. Such damage not only incurs costs for repair or replacement but also leads to long-term consequences, such as data loss in the case of storage devices and downtime for businesses, which can result in substantial financial losses. 
Power surges can originate from several sources, including lightning strikes, switching operations, and faults in the power distribution network. Without adequate protection, these surges can lead to catastrophic failure of sensitive electronics, disrupt critical operations, and pose safety hazards. 

   New Requirements under 18th Edition 

The Institution of Engineering and Technology (IET) Wiring Regulations (BS 7671) have progressively updated their guidance on surge protection devices across editions. The current 18th Edition, last amended in 2022, provides revised guidelines for contractors and establishes new criteria for SPD installation. 
The revised guidance includes a simplified assessment for determining when SPDs are necessary, specifying that: 
“Protection against transient over-voltages shall be provided where the consequence of over-voltage: 
• Results in serious injury to, or loss of, human life; 
• Causes interruption of public services and/or damage to cultural heritage; 
• Leads to interruption of commercial or industrial activity; or 
• Affects a large number of co-located individuals.” 
Additionally, any commercial, industrial, or public building supplied by overhead lines must have surge protection, indicating that the majority of buildings will require SPDs. For residential properties, requirements will depend on usage and occupancy levels. 
Risk Assessment 
For non-residential properties that do not fall into these specified categories, a risk assessment must be conducted. This process has been simplified in the 18th edition, detailed in section 443.4 of the IET Wiring Regulations. The risk assessment involves evaluating the potential impact of a transient over-voltage on the installation and determining the necessity of SPDs based on factors such as the building's usage, occupancy, and the presence of critical equipment. 
If a risk assessment is not conducted, the regulations mandate the implementation of surge protection. This ensures that even in the absence of a formal evaluation, the equipment and infrastructure are safeguarded against possible surges. 
Types of Surge Protection 
All SPDs function by diverting surge currents to earth, thereby reducing the over-voltage to a level that will not damage the system or connected equipment. There are three types of surge protection devices, each designed to address different sources and magnitudes of surges: 
Type 1: Designed to protect against surges resulting from direct lightning strikes. These typically utilize spark gap technology, capable of handling extremely high voltages by creating a short to ground when a specific current level is reached. Type 1 SPDs are installed at the origin of the electrical installation, such as the main distribution board, to provide a first line of defense. 
Type 2: Provides protection against over-voltages from switching operations and indirect lightning strikes. This type commonly employs metal oxide varistors (MOVs) to divert the current. Type 2 SPDs are usually installed at sub-distribution boards to further mitigate the risk of surges reaching sensitive equipment. 
Type 3: Offers localized protection for sensitive equipment. Due to their relatively low discharge capacity, Type 3 devices should always be installed in addition to a Type 1 or Type 2 device. These SPDs are typically placed close to the equipment they are protecting, such as computers or medical devices, providing an additional layer of security. 
Implementation and Compliance 
Ensuring compliance with the 18th Edition of the Wiring Regulations requires a comprehensive approach to surge protection. This involves not only installing the appropriate SPDs but also conducting regular maintenance and inspections to verify their functionality. Electricians and contractors must stay updated with the latest regulations and best practices to effectively safeguard electrical installations. 
Selecting the appropriate type of SPD is critical for ensuring the protection of equipment in all building types, as underscored by the evolving regulatory guidance. By adhering to the 18th Edition of the Wiring Regulations and implementing robust surge protection strategies, building owners and operators can minimize the risk of damage, enhance the reliability of their electrical systems, and protect both human life and valuable assets from the potentially devastating effects of power surges. 
For any more questions leave us a comment below or email us at
MK Wired Team. 
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