Do I Need Surge Protection? 18th Edition BS 7671 Guide

Under BS 7671:2018 Amendment 2, a risk assessment for surge protection is required for all new installations. In practice, the answer is almost always yes — the cost of an SPD is negligible compared to the equipment it protects.

The 18th Edition wiring regulations introduced a formal requirement to consider surge protection on every installation. Amendment 2 (2022) strengthened this further, and Building Regulations Part P now requires SPDs in new residential buildings in England. This guide explains exactly what the regulations require, how to apply the risk assessment, and when an SPD can genuinely be omitted.

What BS 7671 actually says

Regulation 443.4 of BS 7671:2018 requires that for every installation, a risk assessment is carried out to determine whether protection against transient overvoltages is required. The assessment considers: the consequences of failure of equipment in the installation; the overvoltage category of equipment being protected; the lightning flash density at the location; and whether the supply is overhead or underground.

Where the risk assessment indicates that the consequences of a surge event would be unacceptable — which for most domestic and commercial installations means damage to electronics, appliances, or safety-critical equipment — an SPD must be installed. The regulation does not mandate an SPD in every case, but the conditions under which one is not needed are narrow.

The risk assessment in practice

Factor	Lower risk	Higher risk — SPD strongly indicated
Supply type	Underground cable throughout	Overhead supply lines (rural, older networks)
Location	Urban area, low lightning flash density	Rural, elevated, or exposed location
Equipment at risk	Minimal electronics	EV charger, solar inverter, heat pump, smart home equipment, computers
Consequence of failure	Low — easy to replace, no safety risk	High — expensive equipment, safety-critical systems, data loss
Building type	Simple residential, no special requirements	New build (England — Part P requires SPD), HMO, commercial

In reality, virtually every modern domestic and commercial installation meets the criteria for SPD installation when the risk assessment is applied honestly. A house with an EV charger, a solar inverter, a smart meter, computers, and a connected heating system has equipment that is both expensive and sensitive to surge damage. The SPD cost (typically £15–40 for a Type 2 device installed at the consumer unit) is negligible against the cost of replacing even one item of protected equipment.

When Building Regulations require an SPD

Following changes to Approved Document P in England, SPDs are now required at the consumer unit in all new dwellings. This applies to new builds and major rewires in England. Scotland, Wales, and Northern Ireland have separate regulations but the direction of travel is the same — installers in all regions should be specifying SPDs as standard on new and replacement consumer units.

Where exactly is an SPD installed?

A Type 2 SPD is installed within or immediately adjacent to the consumer unit, connected between the incoming live conductors and earth. The WCED WSPD range includes plug-in modules (WSPDT2-CB) and standalone units (WSPD240, WSPD440) designed to fit neatly within standard consumer unit enclosures alongside the main switch and MCBs or RCBOs.

For specific guidance on connection methods and cable lengths, see: How to install an SPD — installer guide

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40kA Type 2 SPDs in 2-pole, 3-pole, and 4-pole — including versions with pre-fitted cables for fast installation. In stock.

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Frequently Asked Questions

Can I omit a surge protection device if the customer doesn't want one?

You can document the risk assessment and conclude that an SPD is not required, but this is increasingly difficult to justify for any modern installation with electronics. The installer carries responsibility for the risk assessment. Where a customer declines an SPD that the risk assessment indicates is needed, this should be documented and the customer should sign to confirm they have declined the recommendation.

Does an SPD need its own OCPD (fuse or MCB)?

Yes — most manufacturers specify that an SPD should be protected by a fuse or MCB on the supply side. The WCED WSPDT2-CB includes a pre-fitted cable set and connection details. The overcurrent protective device prevents the SPD supply cable from being damaged in the event of an SPD failure. Typically a 63A fuse or MCB is used.

Does a surge protector power strip replace a properly installed SPD?

No. Plug-in surge protector strips are Type 3 devices designed to handle the residual surge energy not absorbed by a Type 2 device upstream. They should be used in addition to, not instead of, a properly installed Type 2 SPD at the consumer unit. Without a Type 2 upstream, a plug-in strip may be overwhelmed by a significant surge event.

Further reading:
Type 1 vs Type 2 vs Type 1+2 SPD explained
How to install an SPD — installer guide
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