Section 443 of BS 7671, as amended by Amendment 2 in 2022 and carried forward into BS 7671:2018+A4:2026, requires protection against transient overvoltages in new installations and alterations where a surge could cause serious injury or loss of life, failure of a safety service, or significant financial or data loss, and in all other cases unless the owner of a single dwelling declares that protection is not required. The earlier risk-assessment route was removed. In practice that means a Type 2 surge protective device (SPD) in the consumer unit for almost every new board, with a Type 1 at the origin where the building has a lightning protection system or an overhead supply.
- Since Amendment 2 the default is that an SPD is fitted. The only general exemption is a single dwelling whose owner declines it, and that decision should be recorded.
- SPD types: Type 1 at the origin for direct lightning current, Type 2 at the distribution board for most installations, Type 3 near sensitive equipment and only downstream of a Type 2.
- Install at the origin with leads totalling no more than 0.5 m (Section 534), through the overcurrent device the manufacturer specifies, and check the status indicator.
- Record the SPD type and the status-indicator check on the EIC; note any owner declaration.
- On an EICR, a missing SPD is a C3 at most. A failed SPD is an item for replacement.
What is an SPD and what does it protect against?
An SPD (surge protective device) is connected between the live conductors and earth, presents a very high impedance at normal voltage and a very low impedance when the voltage rises sharply, diverting the energy of a transient to earth and limiting the voltage seen downstream. Transients come from lightning, usually an indirect strike inducing a surge in overhead lines, and from switching operations; they last microseconds and can reach several kilovolts, which is why they damage electronics rather than blowing fuses. Section 443 decides whether an SPD is required and Section 534 how it is selected and erected. Both apply to new work and alterations; neither imposes a duty to retrofit.
When does Section 443 require an SPD?
The 18th Edition in 2018 required SPDs where the consequences of a transient were serious and otherwise allowed a risk assessment based on the supply lines to justify omitting one. Amendment 2 in 2022 removed that assessment. The current Regulation 443.4 position is:
| Situation | Requirement since A2 2022 |
|---|---|
| A transient could result in serious injury to, or loss of, human life | SPD required |
| A transient could result in failure of a safety service (fire alarm, emergency lighting, medical equipment, safety-related control systems) | SPD required |
| A transient could result in significant financial or data loss | SPD required |
| All other cases, including ordinary dwellings | SPD required unless the owner of a single dwelling unit declares that protection is not required |
The single-dwelling exemption is deliberately narrow. It applies to a single dwelling unit, so a block of flats or an HMO is not obviously within it, and it rests on a declaration by the owner, not a decision by the installer. BS 7671 does not prescribe the form of the declaration, but an installer who omits an SPD on the strength of it should have it in writing with the owner's name and date, and record it on the certificate. An agent saying "don't bother" on the phone is not a declaration by the owner.
BS 7671 puts no figure on "significant financial or data loss". A house with a heat pump, PV inverter, battery, EV charger and home network is a lot of expensive electronics on one supply, which is one reason the default became "fit it". For commercial premises the question rarely needs asking.
What are the types of SPD and where does each go?
SPDs are classified by the test they pass under BS EN 61643-11 and by the position in the installation they are designed for.
| Type | Test class | Position | What it does |
|---|---|---|---|
| Type 1 | Impulse current (10/350 µs waveform) | At the origin, before or at the main distribution board | Diverts partial direct lightning current. Required where the building has a lightning protection system to BS EN 62305, and generally where the supply is by overhead line |
| Type 2 | Nominal discharge current (8/20 µs waveform) | At the consumer unit or each distribution board | Limits induced and switching overvoltages to a level equipment can withstand. The standard device for most installations |
| Type 3 | Combination wave | Close to sensitive equipment, within a few metres | Fine protection for electronics; only effective downstream of a Type 2 and often built into socket-outlets or equipment |
For a domestic installation on an underground supply with no lightning protection system, a Type 2 SPD in the consumer unit satisfies Section 443. Where the supply is overhead or there is an LPS, a Type 1 or Type 1+2 device at the origin is needed, and a Type 2 may still be required at sub-boards more than 10 m away. Type 3 devices are an addition, not a substitute.
Where more than one SPD is installed 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 they specify between a Type 1 and a Type 2, or use a combined unit. The voltage protection level Up of the SPD nearest the equipment must be below that equipment's impulse withstand voltage, which under Table 443.2 is 2.5 kV for household appliances and portable tools (overvoltage category II) and 1.5 kV for sensitive electronic equipment (category I).
How is an SPD installed in a consumer unit?
Section 534 governs the installation. The points that matter on site:
- Position. As close to the origin as possible and ahead of any RCD where the arrangement allows, so the SPD's own operation cannot trip it; on a split-load board, a dedicated way fed from the main switch.
- Lead length. Every metre of connecting conductor adds inductive voltage during a surge. Section 534 recommends that the total length (line to SPD plus SPD to earth) does not exceed 0.5 m. Route the earth lead directly to the main earthing terminal or the consumer unit earth bar.
- Overcurrent protection. Fit the device the manufacturer specifies (often a 32 A or 40 A MCB or a fuse) so an SPD that fails short-circuit is disconnected, or use an SPD with integral disconnection.
- Earthing arrangement. On TT systems Section 534 requires a connection type with a spark-gap element between neutral and earth (often called CT2 or "3+1") so the SPD cannot create a fault path the RCD would see. Confirm the SPD is rated for the earthing system.
- Status indicator. Check it after energising and record the check.
- 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.
Consumer unit replacements
Section 443 usually bites in domestic work at the board change: a replacement consumer unit is designed to the current edition, so the SPD question must be answered. Most manufacturers now supply boards with a Type 2 SPD fitted; where the customer declines it, obtain the declaration and note it. A board change is also notifiable under Part P; see Part P Notification Explained: What Electrical Work Is Notifiable.
How is the SPD recorded on the certificate?
The BS 7671 model Electrical Installation Certificate and Condition Report include a box for the SPD type or types fitted (T1, T2, T3) and a tick to confirm the status indicator was checked, and the schedule of inspections has an item for surge protection. Where the owner of a single dwelling has declined the SPD, say so in the comments, or the next inspector will assume it was overlooked. The certificate layout is at Electrical Installation Certificate (EIC) Explained. An SPD fitted with a new consumer unit is part of that EIC; an SPD added alone to an existing board is an addition that can go on a Minor Works Certificate, since no new circuit is created; see Minor Works Certificate: When to Use It (and When Not To).
What does an EICR say about SPDs?
An installation designed before Amendment 2 was not required to have an SPD, and BS 7671 says an installation not complying with the current edition is not necessarily unsafe. Absence of an SPD is therefore not a dangerous defect and cannot be a C1 or C2. Electrical Safety First Best Practice Guide 4 treats it as an improvement recommendation, so record a C3 with a reference to Section 443, or a comment in the summary; either way the outcome is unaffected (see EICR Codes Explained: C1, C2, C3 and FI (with examples)). Where an SPD is fitted, check that the status indicator shows it is healthy, the overcurrent device is of the specified rating and the leads are short and sound. A failed indicator means the SPD has done its job and needs replacing; record it with the action stated.
How Certio helps
Certio produces the EICR, EIC, Minor Works certificate and PAT records on the BS 7671 model forms and turns them into branded PDFs. Photograph the consumer unit and the circuit schedule drafts itself; point the phone camera at a Megger MFT-X1 and the reading goes straight into the schedule of test results, or dictate it while your hands stay on the probes. Suggested observation wording with the regulation reference is there for you to check and confirm. The judgement stays yours; the typing goes. Starter is free for 7 days, then £5 a month.