Regulation 443.4.1 of BS 7671:2018, rewritten by Amendment 2 in March 2022 and carried unchanged into BS 7671:2018+A4:2026, requires protection against transient overvoltages wherever a surge could cause serious injury or loss of life, failure of a safety service, or significant financial or data loss. In every other case an SPD is still required unless the owner of the installation declares that any loss or damage would be tolerable and accepts the risk. The 2018 risk-assessment route and the old single-dwelling carve-out are gone. On site that means a Type 2 SPD in almost every new consumer unit, a Type 1 at the origin where there is a lightning protection system or an overhead supply, and a C3 on an EICR where one is missing.
- Since Amendment 2 the default is "fit it". The only general exemption is a written declaration by the owner of the installation, and it is not available where any of the three mandatory cases applies.
- The opt-out belongs to the owner of the installation, not specifically the owner of a single dwelling. The single-dwelling wording came from the 2018 risk-assessment regulation that A2 deleted.
- Type 1 at the origin for direct lightning current (lightning protection system or overhead line), Type 2 at the consumer unit or distribution board for everything, Type 3 within a few metres of sensitive equipment and only downstream of a Type 2.
- Regulation 534.4.8: total connecting-lead length preferably under 0.5 m and never over 1 m. Fit the overcurrent device the manufacturer specifies, never rely on the cut-out fuse, and use a CT2 device ahead of an RCD on TT.
- A4:2026 changed the forms, not the rules: the model EICR now has schedule item 4.19 for the SPD indicator and a T1/T2/T3/N/A box on the board header.
- On an EICR a missing SPD is C3 at most under Best Practice Guide 4 Issue 7.4; a fitted SPD showing end of life is recorded for replacement.
What is an SPD and what does it actually do?
A surge protective device sits between the live conductors and earth. At normal voltage it is effectively open circuit; when the voltage rises sharply it conducts, diverting the surge energy to earth and clamping the voltage downstream to its protection level, Up. Transients come from lightning, usually an indirect strike inducing a surge on overhead lines or the earth, and from switching of inductive and capacitive loads. They last microseconds and can reach several kilovolts, which is why they wreck electronics without troubling a fuse.
BS 7671 splits the subject in two. Section 443 decides whether protection is required; Section 534 says how to select and erect the device. Both apply to new installations and to additions and alterations. Neither imposes a duty to retrofit an SPD to an existing installation, which is why the EICR position is an improvement recommendation and not a defect.
Table 443.2 gives the impulse withstand voltages the SPD is protecting: 6 kV for overvoltage category IV equipment at the origin, 4 kV for category III distribution equipment, 2.5 kV for category II appliances and portable tools, and 1.5 kV for category I sensitive electronic equipment. A Type 2 device with Up of 1.5 kV or less therefore covers category II equipment with a comfortable margin, which is the design case for a dwelling.
When does Regulation 443.4.1 require an SPD?
The 18th Edition as published in 2018 required SPDs only where the consequences were serious, and otherwise let the designer run a risk assessment on the length of overhead and underground supply line to justify leaving one out. It also said, in the old Regulation 443.5, that no assessment was needed for a single dwelling unit where the value of the installation and equipment did not justify protection. That is where the "single dwelling" phrase that still circulates came from.
Amendment 2 deleted the risk assessment and the single-dwelling carve-out. NAPIT's September 2022 summary of the change put it plainly: dwellings are now considered along with all other installations. The current 443.4.1 position is:
| Situation | Requirement since A2:2022 (unchanged in A4:2026) |
|---|---|
| A transient could result in serious injury to, or loss of, human life | SPD required, no opt-out |
| A transient could result in failure of a safety service as defined in Part 2 (fire detection, emergency lighting, medical, safety-related control) | SPD required, no opt-out |
| A transient could result in significant financial or data loss | SPD required, no opt-out |
| All other cases, including ordinary dwellings | SPD required unless the owner of the installation declares that any loss or damage would be tolerable and accepts the risk |
Regulation 443.4.2 adds a separate duty to consider overvoltage protection where the installation contains equipment likely to produce switching overvoltages above the Table 443.2 withstand levels: motors, transformers, capacitor banks, storage units and high-current loads. In a dwelling that now includes heat pumps, battery storage and EV chargers.
BS 7671 puts no figure on "significant financial or data loss". A house with a heat pump, PV inverter, battery, EV charger and a home office on one supply is a lot of expensive electronics, and the point of the A2 rewrite was to stop the installer having to argue the value question at all. For commercial premises the question rarely needs asking.
Who can decline an SPD, and what counts as a declaration?
The opt-out in 443.4.1 is a declaration by the owner of the installation. Three practical consequences follow.
First, it is the owner's decision, not the installer's and not the tenant's. An agent saying "don't bother" on the phone is not a declaration by the owner. A landlord can decline for a let property, but a tenant cannot decline on the landlord's behalf.
Second, the opt-out is not available where any of the three mandatory cases applies. Mains-powered fire detection in a rented dwelling is a safety service as defined in Part 2, which is why the IET EngX discussion on an EICR of a rented property with no SPD kept coming back to whether the interlinked alarms took the installation out of the "all other cases" row.
Third, BS 7671 does not prescribe a form. The NAPIT article recommends getting the refusal in writing, and that is the only sensible approach: owner's name, address, date, a sentence saying they decline surge protection and accept the risk of damage to wiring and equipment, and a note on the certificate. Without the paper trail the next inspector will assume the SPD was overlooked, and if the owner's equipment is damaged the conversation becomes about what you advised.
What are Type 1, Type 2 and Type 3 SPDs and where does each go?
SPDs are classified by the test they pass under BS EN 61643-11 and by the position they are designed for.
| Type | Test waveform | Position | Job |
|---|---|---|---|
| Type 1 | 10/350 µs impulse current (Iimp) | At the origin, at or before the main distribution board | Diverts partial direct lightning current. Required by 534.4.1.1 where the structure has a lightning protection system to BS EN 62305; manufacturers' selection charts also steer you to a Type 1 or combined T1+T2 where the supply is by overhead line |
| Type 2 | 8/20 µs nominal discharge current (In) | Consumer unit or each distribution board | Limits induced and switching overvoltages to a level equipment can withstand. The standard device for almost every installation |
| Type 3 | Combination wave | Within a few metres of sensitive equipment | Fine protection for electronics; only effective downstream of a Type 2 and often built into socket-outlets or extension units |
For a dwelling on an underground supply with no lightning protection system, a Type 2 SPD in the consumer unit satisfies Section 443. Typical ratings for a single-module domestic kit are In 20 kA, Imax 40 kA, Up 1.5 kV or less and Uc 275 V line to neutral. The Surge Devices installation guide, which is the one most often linked on the IET forum, puts Type 1 duty at 12.5 kA or 25 kA per pole and grades Type 2 devices at 20, 40 or 65 kA by the direct-strike risk of the site.
Where there is an LPS or an overhead supply, a Type 1 or T1+T2 device goes at the origin. Section 534 then asks a second question: equipment more than about 10 m of cable from the upstream SPD can see oscillation that doubles the let-through voltage, so a further Type 2 at a remote sub-board, or a Type 3 near the equipment, is often needed. Type 3 devices are an addition, never a substitute.
Where two SPDs sit in series they must be coordinated so the upstream device takes the bulk of the energy and the downstream device clamps the remainder. Use devices from one manufacturer's range and observe the minimum cable distance or decoupling they specify between a Type 1 and a Type 2, or buy a combined unit and skip the problem.
How does Section 534 say an SPD should be installed?
Section 534 governs selection and erection. The points that catch people on assessment:
Position. As close to the origin as possible. On a split-load board the SPD takes a dedicated way fed from the main switch, upstream of the RCDs, so its own operation on a surge does not trip the whole board. See RCBO vs RCD split-load boards for the board layouts this affects.
Lead length, Regulation 534.4.8. The total length of the connecting conductors, line to overcurrent device, overcurrent device to SPD, and SPD to the earth terminal, should preferably not exceed 0.5 m and must in no case exceed 1 m. Every metre of lead adds inductive voltage during the microsecond rise of a surge, so a device with Up of 1.5 kV on long leads can let through 2 kV or more at the equipment. Route the earth lead straight to the main earthing terminal or the board's earth bar, and keep the loop tight.
Conductor size, Regulation 534.4.10. The Surge Devices guide quotes the BS 7671:2018 minimums as 6 mm² line and neutral with 16 mm² earth for a Type 1, and 2.5 mm² line and neutral with 6 mm² earth for a Type 2, with manufacturers free to specify larger. Fit what the instructions say; the kit above takes 50 mm² tails and 16 mm² earth.
Overcurrent protection, Regulation 534.4.5. An SPD must be protected against overcurrent so that one failing short circuit is disconnected rather than left across the supply. The regulation allows an MCB or fuse on the SPD circuit or a device with integral disconnection, and the Surge Devices guide is blunt that the DNO cut-out fuse must not be relied on because its operation takes the whole supply down. Many current single-module kits carry a thermal disconnect in each cartridge and state that no secondary MCB is required; where the manufacturer specifies a back-up device, fit the rating they give.
Earthing arrangement. On TT systems an SPD ahead of the RCD must be a CT2 or "3+1" connection, a varistor line to neutral and a spark gap neutral to earth, so the device cannot create a line-to-earth fault path that the RCD cannot clear. The IET EngX thread on CT2 SPDs reads Regulation 534.4.6 as requiring exactly that where the SPD is upstream of the RCD, with the alternative of putting the SPD downstream of the RCD. A CT1 device, with its line varistor returned to earth, is fine on TN but not on TT ahead of the RCD. If the kit says "CT2, suitable for all earthing systems" the question is answered; if it does not say, assume it is not. Earthing arrangements TN-S, TN-C-S and TT explained covers how to confirm which you have.
Enclosure. In a dwelling the SPD sits inside the non-combustible consumer unit required by Regulation 421.1.201, not in a separate plastic box on the wall.
Status indicator. Check it after energising and record the check. A red or black window means the varistor has reached end of life and the device is no longer protecting anything.
What does an SPD mean for insulation resistance testing?
Regulation 643.3.2 allows an SPD to be disconnected for the insulation resistance test, or the test voltage dropped to 250 V for an assembled installation where it cannot be. The reason is in the numbers: a domestic SPD has Uc of about 275 V, so a 500 V test makes it conduct and reads as a fault. Disconnect it, test at 500 V, then reconnect it and prove it is back in circuit by the indicator. The full procedure is in the insulation resistance testing guide.
When does the SPD question come up on domestic work?
Consumer unit replacement. A replacement board is designed to the current edition, so the Section 443 question must be answered on every board change. Most manufacturers now sell boards with a Type 2 SPD fitted or as a single-module kit; a Hager Type 2 single-module kit was £29.38 ex VAT at Sparks Direct on 22 October 2026, which is small against the price of the job. Where the owner declines it, obtain the declaration and note it. A board change is notifiable under Part P in England and Wales, see Part P notification, and the certificate choice is covered in consumer unit replacement: what certificate and what to check.
New circuits for high-value kit. An EV charger, PV and battery system or heat pump is exactly the equipment 443.4.2 has in mind for switching overvoltages, and the inverter manufacturers' warranties usually assume surge protection on both the a.c. and d.c. sides. Section 712 asks for d.c.-side SPDs where required, and the PV guide at solar PV installation certificate and the EV guide at EV charger installation certificate cover the detail.
Adding an SPD to an existing board. This is an addition that does not create a new circuit, so a Minor Works Certificate is appropriate; see Minor Works Certificate: when to use it. Check the spare way is fed from the main switch side, that the board's earth bar is the right end of the run, and that the lead lengths stay under 0.5 m.
How is the SPD recorded on the A4:2026 forms?
The IET's A4:2026 model Electrical Installation Certificate and Condition Report record the SPD in two places. The distribution board header has an "SPD details" box with tick boxes for T1, T2, T3 and N/A, and the form's footnote says to tick both type boxes for a combined T1+T2 or T2+T3 unit and to enter a Type 3 device protecting sensitive equipment in the remarks column of the schedule of test results. Next to it is a line to confirm the SPD operational status, with the note that not all SPDs have visible functionality indication.
On the EICR, the A4 schedule of inspections for a residential installation up to 100 A carries item 4.19, "Confirmation of indication that SPD is functional (651.4)". The notes for recipients add that where an SPD is installed the status indicators should be checked against the manufacturer's information and expert advice sought if the device is shown as not operational.
Where the owner of the installation has declined an SPD, say so in the comments or the design section of the EIC, and name the owner and date of the declaration. The EIC layout is at Electrical Installation Certificate explained.
What does an EICR say about SPDs?
An installation designed before Amendment 2 was not required to have an SPD, and the introduction to BS 7671 is explicit that an installation not complying with the current edition is not necessarily unsafe. Absence of an SPD is not dangerous to people, so it cannot be a C1 or C2. Electrical Safety First's Best Practice Guide 4, Issue 7.4 of August 2026, lists "Absence of Surge Protective Device (SPD) where required by 443.4.1 (a) & (c)" as C3, improvement recommended. It is the only SPD entry in the guide. Record it as C3 with the regulation reference, or as an uncoded comment where you judge the owner would decline anyway; either way the report outcome is unaffected. The coding logic is in EICR codes explained and the wording in how to write EICR observations.
The IET EngX threads on this show how little agreement there is beyond that. On an EICR with no SPD, contributors settled on C3 or no code, with one arguing that Chapter 65 imposes no duty to recommend improvements at all. On a board with an SPD showing red in both windows, the view was that the device had done its job, there was no danger to people, and the right record was an observation that the SPD has reached end of life and should be replaced, with the client told plainly. Either way, do not code a dead SPD as C2 and do not ignore it.
Where an SPD is fitted, item 4.19 asks you to confirm the indicator, so check it, check the overcurrent device is the rating specified, check the leads are short and sound, and confirm a CT2 device on TT ahead of the RCD. A CT1 device ahead of the RCD on TT is a design error worth an FI or C3 with a note, because a failed line varistor would put line to earth with only the electrode to clear it. The full inspection sequence is in how to do an EICR step by step.
How Certio helps
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