What is a surge protective device or SPD?
A surge protective device (SPD) limits transient overvoltages: brief voltage peaks that can damage electrical equipment [S1]. Your designer assesses the installation and selects coordinated protection. The IET's guidance on BS 7671:2018+A4:2026 explains that SPDs themselves need suitable short-circuit protection [S2]. Ask what protects the supply route to your outdoor chargers and how it will be maintained. Checked October 2026.
What does surge protection do for your site?
A surge protective device (SPD) limits short-lived voltage peaks, called transient overvoltages, which can damage equipment. These can arise from lightning effects or switching electrical loads [S1].
For your site, it matters because working chargers and control equipment may be exposed through their electrical connections. Ask the designer to identify the equipment and circuits being protected, including chargers outdoors. The Section 722 guide covers the wider charging installation.
When does BS 7671 expect surge protection?
The IET’s corrected explanation of Regulation 443.4.1 identifies serious injury and significant financial or data loss as consequences requiring protection. For other cases, it describes protection unless the owner accepts tolerable damage and consequential loss [S3]. Do not treat the location outdoors as the only question, or an owner declaration as permission to omit protection in every case.
Ask for the current design basis and a written explanation of the consequences assessed. This is a technical overview; check contractual or legal responsibilities with your solicitor.
How are SPDs selected for a charger installation?
Selection includes coordinated devices across the installation [S1]. Ask which distribution boards and charger circuits the proposal covers. Request the selected device details rather than accepting a generic “surge protection included” line.
Under the IET’s explanation of BS 7671:2018+A4:2026, the SPD also needs appropriate short-circuit protection, following its manufacturer’s instructions [S2]. Keep that selection with the electrical installation records and agree who checks the protection during charger maintenance. Keep operating assumptions in the charging cost tool separate from the protection design.
Next step
Include your existing protection records in the site check, then get matched with an installer that covers your area.
Piggy Pineapple Ltd operates this referral service. We refer enquiries to installer partners and may be paid a fee. Our owner holds shares in at least one partner. Before sharing your details, we name the proposed partner and disclose any shareholding in it.
Common questions
Can switching equipment cause a surge without lightning?
Yes. The IET describes transient overvoltages from electrical switching as well as atmospheric events [S1].
Does a Type 3 SPD replace distribution-board protection?
No. The IET describes Type 3 devices as supplementary to Type 2 protection. Have the designer coordinate devices across the installation [S1].
Does an SPD need a separate fuse or breaker?
Short-circuit protection may be internal or external. The IET says to follow the SPD manufacturer's instructions when specifying the arrangement [S2].
Can the network fuse protect the SPD?
Sometimes, subject to the conditions described in the IET's explanation. Ask the designer to document why the upstream protection is suitable [S2].
Will charging stop if the SPD's protective fuse operates?
Not necessarily. The IET describes arrangements where supply continues after that operation, leaving equipment exposed to further overvoltages. Include inspection in maintenance [S2].
Ask about your site
Sources
- Surge Protective Devices, Institution of Engineering and Technology,Last checked 19 October 2026
- Do SPDs require an overcurrent protective device?, Institution of Engineering and Technology,Last checked 19 October 2026
- On-Site Guide errata - surge protection requirements, Institution of Engineering and Technology,Last checked 19 October 2026