The short answer
Adding a Type 2 surge protection device (SPD) to a consumer unit typically costs around £80–£200 supply and fit when done as part of a consumer unit replacement, and can run £100–£300 or more as a standalone addition to an existing board, including the device, labour and any testing. The 18th Edition of BS 7671 (Amendment 2, 2022) introduced a requirement to include or formally risk-assess the omission of an SPD in most new domestic installations, so many electricians now fit one as standard during a consumer unit replacement. The device itself — typically a compact module that clips into a spare way — costs around £30–£80 at trade; the balance is labour and the time to verify it is correctly installed and coordinated with the board.
Surge protection devices are a relatively recent addition to standard UK domestic electrical practice. Here is what they do, when they are now expected, and what the cost looks like in practice.
Surge protection at a glance
- Type 2 SPD (supply and fit)~£80–£200 with consumer unit job
- SPD standalone addition~£100–£300 fitted
- BS 7671 requirement (18th Ed. A2)risk assessment or SPD for most new installs
- Device cost (trade)~£30–£80 depending on rating
- Protection fromtransient overvoltages (surges)
What an SPD does and why it matters
A surge protection device is designed to limit the damage caused by transient overvoltages — brief, sharp spikes in the mains voltage that can exceed normal limits. These surges can originate externally (from lightning strikes or switching events on the distribution network) or internally (from large loads switching on and off within the property). Modern homes contain a significant amount of sensitive electronics — smart TVs, home hubs, inverters for EVs and solar, and networked appliances — that can be damaged or destroyed by surges that a conventional MCB or RCD would not interrupt, because the spike is too fast and too brief for those devices to react to.
A Type 2 SPD at the consumer unit provides whole-house protection at the point where the supply enters the domestic circuits. It works by diverting the surge energy to earth before it can propagate around the wiring. It does not protect against a direct lightning strike on the property, for which Type 1 protection at the service head would be relevant, but it addresses the transient overvoltages that occur on a normal supply.
| SPD scenario | Typical cost | Notes |
|---|---|---|
| Type 2 SPD added during CU replacement | £80–£150 extra | Lower cost than standalone visit |
| Type 2 SPD retrofitted to existing CU (standalone visit) | £100–£250+ | Includes callout, fitting, testing |
| Type 1+2 combined SPD (at main incomer) | £200–£400+ | For higher-exposure or larger properties |
| SPD device only (trade supply) | £30–£80+ | Depending on brand and rating |
| Labour for standalone SPD fit | £70–£150 | Per electrician's hourly or callout rate |
Indicative UK figures for guidance. Sources: Checkatrade trade cost guides; IET BS 7671 18th Edition Amendment 2 guidance. Actual costs depend on board type, access and electrician's rates.
What BS 7671 18th Edition Amendment 2 says
The 18th Edition of BS 7671 (the IET Wiring Regulations, most recently updated by Amendment 2 in 2022) introduced Regulation 443 covering protection against transient overvoltages. For most new installations and for consumer unit replacements, this now requires the designer or installer to either:
- Install a Type 2 SPD at the origin of the installation; or
- Document a risk assessment showing why an SPD is not needed in that specific case.
In practice, the risk threshold calculation for a typical UK semi-detached or terraced house — with overhead distribution cables and modern electronics — usually concludes that an SPD is required. As a result, most electricians fitting a new consumer unit under current regulations either include an SPD as standard or quote it as a recommended addition with a clear explanation if the client declines.
If an electrician proposes to replace your consumer unit without mentioning an SPD at all, it is worth asking whether the installation will comply with the current edition of BS 7671 on that point.
Choosing and specifying an SPD
Not all SPDs are identical, and the right one for your installation depends on the supply characteristics, the equipment being protected and the risk assessment. A registered electrician carrying out a BS 7671-compliant consumer unit replacement should specify the SPD as part of the installation design, not simply fit the lowest-priced available device.
Key points to understand:
- Type 2 vs Type 1+2: a Type 2 SPD protects against surges arriving on the distribution network; a combined Type 1+2 device also handles a direct lightning strike on the service head. For most UK homes, a Type 2 device is what is relevant.
- Iimp and In ratings: the device should be rated for the likely surge energy at your installation. Your electrician selects this based on BS 7671 Regulation 443.
- Status indicator: better-quality SPDs include an indicator that shows if the device has operated and needs replacement after a significant surge event.
Frequently asked questions
Is a surge protection device mandatory under UK wiring regulations?
Under BS 7671 18th Edition Amendment 2 (2022), an SPD is required — or a formal risk assessment must document why it is not — for most new and replacement domestic installations. In practice, this means most consumer unit replacements should include an SPD or a written risk assessment explaining the omission.
Can I add an SPD to my existing consumer unit without replacing the whole board?
Yes, provided there is a spare way in the existing consumer unit to mount the SPD and the board is modern enough to accommodate one. A registered electrician can assess whether your board allows this. The total cost for a standalone SPD retrofit is typically higher per device than adding one during a full board replacement, because of the callout and labour overhead.
Does an SPD protect against lightning?
A Type 2 SPD at the consumer unit protects against transient overvoltages arriving on the distribution network, which includes indirect lightning effects. It does not fully protect against a direct lightning strike on the property or service head, for which Type 1 protection is the relevant category. Direct strikes are a rare and extreme event; transient surges are much more common.
Sources & further reading
- IET — BS 7671 18th Edition (2018 + Amendment 2, 2022)
- Electrical Safety First — consumer unit replacement best practice guide
- Checkatrade — cost of replacing a fuse box / consumer unit
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property and installation. They are guidance, not a quotation.