Surge Protection Devices (SPDs): When They Are Required Under BS 7671 Amendment 2

Quick Answer: Since 28 March 2022, BS 7671:2018+A2:2022 has required Surge Protection Devices on virtually all new and rewired installations. Regulation 443.4.1 deletes the old risk-assessment escape route and only allows omission where the owner declines protection in writing — and that refusal is itself blocked if the installation feeds any safety service such as a mains-wired smoke alarm. A Type 2 SPD module fitted at the consumer unit is the standard domestic specification.

Summary

Amendment 2 settled a long-running argument. Under the original 18th Edition, designers could fill in a Clause 443.5 risk calculation and, often enough, decide an SPD was unnecessary. That paragraph is gone. The replacement text in 443.4.1 turns the question on its head: protection is required unless an explicit, written, owner-driven refusal is on file. That single change is why modern domestic boards almost always carry an SPD module today.

For most electricians the practical impact is operational rather than philosophical. The cost of a Type 2 SPD is small against the labour of a consumer unit change, the paperwork to document a refusal is more nuisance than the device itself, and the safety-service hook (mains-wired smoke alarms in nearly every house) means the option to refuse is rarely available anyway. Treating SPD as standard kit on every new board avoids ambiguity, protects sensitive electronics from common-mode transients, and keeps the certificate clean.

Owners and homeowners reading this looking up "do I need surge protection in my fuse box" should understand: this is now electrician's regulation default behaviour, not an upsell. If a quote excludes it, ask why and expect to sign something formally if you want it left out.

Key Facts

Quick Reference Table

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Scenario SPD requirement Regulation hook
New domestic install with mains smoke alarm Mandatory 443.4.1 (safety service)
Domestic rewire, no safety service Required unless written refusal 443.4.1 / 443.4.2
Consumer unit change only (CU swap) Required at the new CU 443.4.1
Single-circuit addition to existing CU (no SPD upstream) Risk-assessed; generally fitted 443.4 GN
Building with external LPS (BS EN 62305) Type 1 (or Type 1+2) at origin 534.4.1.1
Overhead supply (rural) Type 1+2 typical 443.4.1 + DNO advice
Fed from underground supply, urban TN-C-S Type 2 typical 443.4.1
Commercial premises with significant data/IT load Type 2 at board + Type 3 at racks 443.4.1 (consequential loss)
Premises with medical equipment Mandatory; consider redundancy 443.4.1 (loss of life)
Listed dwelling, owner declines Permitted only with written declaration; not allowed if safety service present 443.4.2
SPD type Typical Iimp / In Up (residual voltage) Where it goes
Type 1 Iimp 12.5–25 kA (10/350 µs) ≤ 2.5 kV typical Origin / main switchgear, especially with LPS
Type 2 In 8–20 kA (8/20 µs) ≤ 1.5 kV typical Consumer unit / sub-distribution boards
Type 1+2 Iimp 12.5 kA + In 20 kA ≤ 1.5 kV typical Consumer unit where origin protection also needed
Type 3 In ≤ 5 kA ≤ 1.5 kV Final-circuit point-of-use, near sensitive load

Detailed Guidance

Why the rules changed

The old risk-calculation route (CRL value) gave designers a numerical out. In practice it was used inconsistently — many spreadsheets returned "not required" almost regardless of input, and certifiers had limited ability to challenge the assumptions. The Joint IET/BSI committee deleted the route because the underlying surge environment had changed: ubiquitous low-voltage electronics, mains-connected smoke alarms, broadband routers and inverter-driven appliances are far more transient-sensitive than the 1990s loads that originally informed the risk method. The committee's view was that the cost of an SPD module is now low enough, and the consequence of an unprotected transient high enough, that protection should be the default.

The change does not retrospectively require existing properties to be fitted with SPDs — there is no equivalent of a Part P amnesty deadline. But every notifiable job, every consumer unit change, and every rewire that brings work under the current edition must comply.

Choosing the right SPD type

Type selection is not about premium specification — it is about matching the device to the impulse it has to clamp.

Coordinating devices through the system

If the installation has multiple SPDs (origin + DB + point-of-use), they must coordinate so that the upstream device clamps the bulk of the energy and the downstream device shaves the residual. Manufacturers publish coordination tables; mixing Type 1 from one brand with Type 2 from another without checking the published tables is a competence question — if the impulse cannot transfer cleanly between them, the downstream device may fail before the upstream one starts to conduct.

Installation rules that catch out new electricians

TT installations need extra care

On TT supplies the SPD has to ride out a Temporary Overvoltage event caused by a fault on the LV neutral. A standard TN-rated Type 2 will fail under this condition — on TT use specifically TOV-rated devices (BS EN 61643-11 product class T2 with a declared UTOV value). This is one of the few areas where the specification differs by earthing system.

Consumer-facing question — "is surge protection just an upsell?"

Homeowners often ask whether a quote that includes "SPD" is the electrician adding optional kit. Under the current Wiring Regulations it is not. For any new consumer unit fit since March 2022, an SPD is the regulatory baseline. A quote that omits it should either reference Regulation 443.4.2 and a written customer refusal on file, or it is missing scope. On a 10–14 way modern board the parts cost is normally £45–£90 and the installation labour adds 15–30 minutes — not a meaningful proportion of a £700–£1,200 consumer unit replacement.

Frequently Asked Questions

Do I have to retrofit SPDs to an existing house?

No — there is no retrospective requirement. Existing installations stay compliant under the edition they were installed to, providing no notifiable work has been undertaken since. The duty bites on the next consumer unit change, rewire, or notifiable addition.

Can I fit the SPD on a free way of an existing CU rather than upgrade the board?

Yes, providing the existing CU has spare capacity, the manufacturer approves the device for that enclosure, and the connecting lead length rule can be respected. Many older boards do not have practical room for short Phase + PE leads to a side-mounted SPD module, in which case the SPD is part of the case for a CU replacement.

What about RCBO boards — does each RCBO need its own SPD?

No. SPDs and RCBOs do different jobs. A single Type 2 SPD at the busbar protects every downstream RCBO and circuit. There is no requirement, regulatory or technical, for per-circuit SPDs.

Does a portable plug-in surge protector (Type 3 strip) replace a board-mounted SPD?

Not in a code sense. Type 3 strips clamp residual transients close to sensitive equipment but are not rated for the impulse currents at the origin or distribution board. They are a complement to a Type 2 SPD, not a substitute, and they have no recognised compliance status under 443.4.1.

Can I claim on my insurance if surge damage occurs and I have no SPD?

Most home insurance policies will pay out for accidental electrical damage regardless of whether an SPD is fitted, provided the wiring meets current standards at the date of installation. Some commercial policies exclude consequential loss for IT equipment if no SPD is fitted — read the policy schedule.

Regulations & Standards