Surge protection device (SPD)
Plain English. Practical detail. UK context.
A surge protection device limits transient overvoltages: brief voltage surges which can damage an electrical installation or connected equipment. An SPD is different from an RCD or an overcurrent breaker. It is one part of a coordinated protection arrangement, not a guarantee against every consequence of lightning or a supply fault.
Safety: use a registered electrician, for example one registered with a competent person scheme such as NICEIC or NAPIT, for electrical installation work. Do not remove covers or open electrical equipment yourself.
Last reviewed: (editorial review against the public sources listed below).
Why it is considered
Sensitive electronics are present in heating controls, appliances, computers and security equipment, not just televisions. Surges can cause immediate failure or less obvious damage. The IET explains that other incoming services can also provide routes into a building, so protecting the mains alone may not address every exposure. The designer considers the property, its equipment and the consequences of interruption. Buying an extension lead marketed as surge protected does not settle the design of protection at the installation origin.
Types and coordination
The IET's consumer guidance distinguishes Type 1, Type 2 and Type 3 devices. They have different duties and locations, and protection close to sensitive equipment may supplement upstream protection rather than replace it. Multiple devices need coordination, with compatibility confirmed by the installer and manufacturers. Cable routing and the installation arrangement matter as well as the product name. A consumer unit with a spare module is not evidence that any SPD can be fitted without further assessment.
Questions for a homeowner
Ask which parts of the installation and which incoming services the proposal addresses. Find out whether the device has a status indicator, what that indicator means and who should act if it shows replacement is required. SPDs can have replaceable elements, but the instructions determine the arrangement. Do not open the consumer unit to check a cartridge. Keep the exact product reference with the installation records so later maintenance is based on the correct device rather than a similar-looking substitute.
Current requirements, not an old checklist
The IET identifies BS 7671:2018+A4:2026 as current after the October 2026 transition. Some freely available consumer summaries still describe earlier editions, so they should not be used as the sole decision tree for omitting protection. Ask the designer to apply the current requirements to the actual project and document the choice. For an existing board, confirm compatibility and the certification for the alteration. This reference explains the function; it does not claim a universal exemption, a guaranteed equipment-saving figure or an installed UK price.
Frequently asked questions
Is an SPD the same as a lightning protection system?
No. Surge protection and external lightning protection address connected but different aspects of risk. Specialist coordination may be necessary.
Does fitting one remove the need for an RCD?
No. Residual-current protection serves a different purpose and must be provided where required by the installation design.
Sources and further reading
Public sources and further reading. Sources checked: 8 November 2026. Consult the original for details and later changes.