SPDs and Overcurrent Protection in Homes

SPDs and Overcurrent Protection in Homes — Has the Debate Finally Been Settled?

The question has been doing the rounds on forums, in training rooms, and across social media for a while now: does an SPD installed in a domestic consumer unit actually need its own dedicated overcurrent protective device (OCPD)?

In January 2026, the ENA and BEAMA published a joint statement to try and put the argument to bed. It's helpful — but it raises as many questions as it answers. Let's break it down.

A Bit of History First

Before we get into OCPDs, it's worth recapping how we ended up here — because the SPD story in BS 7671 has had more plot twists than most.

When Amendment 2 landed in March 2022, it removed the risk assessment process entirely, and with it the special dispensation that had previously exempted single dwellings. SPDs were now effectively required across all installations.

The new position under A2 was that protection against transient overvoltages must be provided where the consequence of overvoltage could result in serious injury to or loss of human life, failure of a safety service as defined in Part 2, or significant financial or data loss. For all other cases, SPDs shall be fitted unless the installation owner declines the protection and accepts the risk.

That second indent — failure of a safety service — caused immediate and significant confusion. The Part 2 definition of a safety service covers any system provided to warn persons in the event of a hazard, or essential to their evacuation. That meant any consumer unit supplying a mains-wired smoke alarm technically required an SPD — and domestic installations were no longer exempt.

You can see where this was heading. Almost overnight, the installation of a simple domestic smoke alarm potentially triggered a requirement for surge protection. Landlords, installers, and manufacturers were understandably alarmed — and not without good reason.

The Corrigendum That Put Things Right

The Fire Industry Association stepped in, arguing that fire detection and alarm equipment — both commercial systems under EN 54 and domestic smoke alarm devices under BS EN 14604 — already incorporates built-in EMC immunity to transient events, in compliance with The Electromagnetic Compatibility Regulations 2016. Lightning surges were not a new phenomenon, and the requirement for SPDs on such equipment had never been the intention of the regulation.

The FIA's advocacy was successful, and a corrigendum was published on 15 May 2023, correcting the unintended requirement. The change was welcomed across the board — by installers, landlords, and manufacturers alike, who had been fielding a sharp increase in calls about the SPD requirement ever since A2 was published.

So the short version: domestic smoke alarms, heat alarms, and CO alarms do not require SPD protection — the corrigendum put that to bed. But the broader requirement for SPDs in domestic installations remained firmly intact.

Where We Stand Now

With the safety services definition tidied up, the practical reality is that most domestic consumer units still need an SPD. The opt-out route exists in theory — but it requires the installation owner to formally declare that they accept the risk of damage to both wiring and connected equipment. In practice, that's a document most homeowners won't want to sign, and most installers won't want to rely on.

SPDs are therefore going in everywhere. Which makes the question of how to install them correctly all the more important — and that's where the overcurrent protection debate comes in.

Where the OCPD Confusion Comes From

BS 7671 Regulation 534.4.5 is clear in its intent: the designer needs to determine whether the SPD has internal overcurrent protection, and if not, dedicated overcurrent protection is required for short-circuit currents. That's the baseline.

The problem is that manufacturers have been muddying the water for years. A number of SPDs on the market have been marketed with claims like "no MCB required" — and while some of those devices do contain internal protection of some description, the means by which it works isn't always obvious. Meanwhile, BS 7671 Fig 534.5 shows OCPD 1 (the DNO cut-out fuse) and OCPD 2 (a dedicated upstream MCB or fuse for the SPD) as part of the diagram. Some installers have been fitting both without question. Others have been skipping OCPD 2 entirely — because the manufacturer said they could, or because space in the consumer unit was tight.

Inconsistent interpretation has been driving inconsistent installation practice. And that needs to stop.

What the ENA/BEAMA Statement Actually Says

The joint statement clarifies that OCPD 2 in BS 7671 Fig 534.5 may be omitted and OCPD 1 — the DNO cut-out fuse — used for the short-circuit protection of the SPD, where all of the following conditions are met:

• the SPD is in a household or similar installation;
• it is installed inside a single-phase consumer unit conforming to BS EN (IEC) 61439-3, or
• inside an enclosure with a switch-disconnector conforming to BS EN (IEC) 60947-3 — both requiring a rated conditional short-circuit current of 16 kA;
• the SPD conforms to BS EN 61643-11;
• the manufacturer's instructions confirm that OCPD 2 can be omitted and specify the required OCPD 1 characteristics;
• and the SPD does not require withdrawal of the DNO cut-out fuse for its replacement or maintenance.

The statement also confirms that relying on the DNO's cut-out fuse does not breach the Electricity Safety, Quality and Continuity Regulations — specifically Reg 25 regarding making or altering a connection. The DNO fuse remains owned and maintained by the DNO and is not changed by the installer.

So far, so reasonable.

The Good: Clarity for Domestic Installs

For the majority of domestic installations, this is genuinely useful guidance. If your SPD meets all five conditions, you can legitimately omit the dedicated OCPD 2 — no separate MCB, no additional enclosure, and a cleaner installation inside an already cramped consumer unit.

That 16 kA conditional rating is qualified using a 100 A BS 88-3 fuse, which also covers the 60 A and 80 A ratings found across most domestic supplies. For the overwhelming majority of household board changes, this should be achievable.

The Bad: It's Not a Blanket Permission

Here's what the statement is not — it's not a green light to ditch OCPD 2 on every job regardless of the SPD you're fitting.

All five conditions must be met. Every single one. If the manufacturer's instructions don't explicitly state that OCPD 2 can be omitted, you cannot rely on this guidance to justify skipping it. If your consumer unit doesn't carry the 16 kA conditional rating, the same applies.

This means the installer still needs to read and understand the manufacturer's datasheet before making the decision. That sounds obvious — but under time pressure on a busy board change, it's exactly the step that gets skipped. And that's where installations end up that look fine on the surface but aren't backed up by any documented design rationale.

The Elephant in the Room: What Happens When OCPD 2 Operates?

One issue the statement doesn't address is the practical consequence of OCPD 2 operating — wherever it's present. If a dedicated MCB trips because the SPD has absorbed a significant surge hit, the occupant is unlikely to notice anything unusual. The lights are still on. The boiler still fires. But the surge protection is gone — and nobody knows.

Until the next surge takes out the EV charger, the smart home hub, or the heat pump controller.

This isn't an argument against having an OCPD. It's an argument for status indicators and for making sure homeowners understand what an SPD is and why they should check it periodically. The visual indicator on most modern SPDs exists for exactly this reason — but only if someone actually looks at it.

What This Means for You

• Check the manufacturer's datasheet before deciding whether OCPD 2 is required. Don't assume — verify.
• If all five ENA/BEAMA conditions are met, you can legitimately rely on the DNO cut-out fuse and omit a separate MCB for the SPD.
• If they're not all met, OCPD 2 stays. No shortcuts.
• Brief the customer on the SPD — what it does, where the status indicator is, and what to do if it shows a fault.
• Document your design decision. Whether you include or omit OCPD 2, note why. It protects you and demonstrates competence.

Final Thoughts

The road to where we are now has been a bumpy one — from the confusing original A2 position on safety services, through the FIA corrigendum that corrected the unintended consequences, to the ENA/BEAMA joint statement trying to bring clarity to overcurrent protection. It's taken a lot of industry effort to get to something approaching a coherent position.

The joint statement is welcome. But it's guidance, not a universal exemption. The conditions are precise and they need to be treated as such.

SPDs are a standard feature of domestic installations now. The confusion around overcurrent protection has been a source of unnecessary risk for too long — and the installers caught in the middle have been the ones carrying that risk.

Read the datasheet. Meet the conditions. Document the decision.

It's not complicated — but it does require electricians to actually engage with the detail. That's non-negotiable.