SPD Surge Protection UK — Type 1, 2, 3 Explained

Surge Protection Devices clamp transient overvoltages on your installation. A typical surge — from lightning, switching transient, or grid fault — can briefly push 6 kV-10 kV onto a 230V circuit, frying electronics.

Without SPD, your installation absorbs the surge through whatever's plugged in — usually the cheapest LED driver or smart plug, then cascading damage.

With SPD, the spike is shunted to earth before reaching downstream equipment. Surge damage drops to near zero for non-direct strikes.

BS 7671:2018 Amendment 4 (April 2026) expects an SPD assessment on every new install. Most domestic installs need Type 2.

Type 1 SPDs handle direct lightning strikes. Required where the supply enters via overhead lines and lightning protection is fitted.

Rarely needed in London — most supplies are underground. Outer-borough properties with overhead supplies may need Type 1.

Cost: £150-250 per phase. Bulky — requires dedicated DIN space in the fuse board.

If your property has lightning protection (LPS) on the roof, you almost certainly need Type 1.

Type 2 handles indirect lightning and switching transients. Required for most modern UK installs.

Goes at the main intake — first DIN slot in the consumer unit, fed directly from the main switch.

Cost: £80-130 trade, £120-180 installed.

In a 12-way Hager Design 50 board, Type 2 SPD takes 1-2 DIN slots. Plan for this in any new fuse board upgrade.

Type 3 SPDs are local — installed near sensitive equipment (servers, AV racks, medical gear). They handle the residual transient after the Type 2 has done its work.

Rarely needed in a domestic context. Common in commercial and home-office setups with significant electronics.

Cost: £40-80 per device, plus install time.

Most consumer surge-protected power strips are Type 3 equivalents. Quality varies wildly — proper Type 3 in a DIN enclosure is genuinely protective.

Underground supply, no lightning protection — Type 2 at intake. £120-180 installed. Most London homes.

Overhead supply (some outer-borough properties) — Type 1+2 combination at intake. £250-400 installed.

Home office with rack of equipment — Type 2 at intake + Type 3 at the rack. £200-300 total.

Commercial premises with significant electronics — Type 1+2 at intake + Type 3 at critical loads. £400-700 typical.

When booking a fuse board upgrade, explicitly request 'Type 2 SPD on the intake'. Most contractors include it by default in 2026 but some skip to save cost.

Verify the SPD is connected to the supply side (before the main switch) where required by the manufacturer. Some Hager Design 50 SPDs connect downstream of the main switch — check the manual.

SPD has a finite life. The device contains MOVs (Metal Oxide Varistors) that degrade with each clamp event. Most SPDs have a status indicator (green = healthy, red = replace). Check at every EICR.

Replacement after a major surge event is mandatory. The SPD is sacrificial — once it's clamped a major spike, it's no longer reliable.