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

Surge Protection

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

BS 7671 makes you consider protection against transient overvoltages on every installation. For almost every modern home or commercial site, that assessment ends the same way: fit an SPD.

Quick answer

Under BS 7671:2018+A2:2022, protection against transient overvoltages has to be considered on every installation. In practice the answer is almost always yes: an SPD costs little compared with the equipment it protects.

What BS 7671 says

Section 443 of BS 7671:2018+A2:2022 deals with protection against transient overvoltages. The assessment looks at the consequences of equipment failure, the overvoltage category of the equipment, the lightning flash density at the location, and whether the supply is overhead or underground.

Where the consequences of a surge would be unacceptable, an SPD is needed. For most homes and commercial sites that means damage to electronics, appliances or safety-critical equipment, so the cases where an SPD can genuinely be left out 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, HMO, commercial

Applied honestly, virtually every modern home or commercial site meets the criteria. A house with an EV charger, solar inverter, smart meter, computers and a connected heating system has equipment that is both expensive and sensitive to surges. An SPD is a small cost against replacing even one protected item.

New builds and Building Regulations

Electrical work in new dwellings has to meet BS 7671, so the surge protection assessment above applies to new builds and major rewires. Scotland, Wales and Northern Ireland have separate regulations, but the direction is the same: installers everywhere should specify SPDs as standard on new and replacement consumer units.

Where is an SPD installed?

A Type 2 SPD goes in or right beside 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) that fit alongside the main switch and MCBs or RCBOs. For connection methods and cable lengths, see how to install an SPD.

Shop WCED Type 2 SPDs

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

View the SPD range

Frequently asked questions

Can I leave out a surge protection device if the customer doesn’t want one?

You can document a risk assessment that concludes an SPD isn’t needed, but that is increasingly hard to justify for any installation with electronics. The installer carries responsibility for the assessment. If a customer declines an SPD the assessment says is needed, record it and have the customer sign to confirm.

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

Yes. Most manufacturers specify a fuse or MCB on the supply side of the SPD, typically 63A, to protect the SPD supply cable if the SPD fails. The WSPDT2-CB includes a pre-fitted cable set and connection details.

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

No. Plug-in strips are Type 3 devices that deal with residual surge energy left over from a Type 2 device upstream. Use them in addition to a Type 2 at the consumer unit, not instead of one. Without a Type 2 upstream, a strip can be overwhelmed by a large surge.

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