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Type 1 vs Type 2 vs Type 1+2 SPD Explained

Surge Protection

Type 1 vs Type 2 vs Type 1+2 SPD Explained

Surge protection devices come in three categories, defined by where they sit in the installation and how large a surge they are built to handle. Most UK homes and commercial sites need a Type 2 SPD at the consumer unit as a minimum.

Quick answer

Type 2 at the consumer unit is the standard for UK homes and commercial sites. Add Type 1, or a combined Type 1+2 unit, where there is a lightning protection system or overhead supply cables.

The three SPD categories

Electrical surges are brief overvoltage transients caused by lightning, grid switching or large motor loads. They are a common cause of electronic equipment failure and can contribute to electrical fires. SPDs divert the excess voltage safely to earth before it reaches connected equipment or wiring.

The three categories describe where in the supply chain a device is installed, not simply how powerful it is. Getting that right is central to specifying protection under BS 7671:2018+A2:2022.

SPD types along the supply chain Type 1 at the origin, Type 2 at the consumer unit, Type 3 at the point of use.Type 1Origin of installationType 2Consumer unit / boardType 3Socket or equipmentStandard for UK homesDirect or near-direct lightningIndirect surges and switchingResidual surges
The three SPD types, from the point where the supply enters the building to the equipment itself.
Type Location Impulse rating Protects against Standard
Type 1 Origin of installation, at the main incomer before the consumer unit 25–50 kA (Iimp) Direct or near-direct lightning strikes on the building or service cables BS EN 61643-11
Type 2 Consumer unit or distribution board 5–40 kA (Imax) Indirect lightning surges and switching transients from the grid or inside the building BS EN 61643-11
Type 3 Point of use, at the socket or equipment <5 kA Residual surges not fully absorbed by upstream Type 1 or Type 2 devices BS EN 61643-11

Type 1: when is it required?

Type 1 SPDs are needed when a building has a lightning protection system (LPS), when the supply comes in on overhead cables rather than underground ones, or when the site is at raised risk of a direct strike, such as isolated buildings, tall structures or areas with high lightning ground flash density. For a standard UK home with an underground supply and no LPS, Type 1 is not normally required.

Type 1 devices sit upstream of the consumer unit, at or near the service head or meter position, and are usually paired with a coordinated backup overcurrent device. Where that means working at the supply position, speak to your DNO first.

Type 2: the standard for UK homes and commercial sites

Type 2 SPDs are fitted at the consumer unit or distribution board. They cover the most common surge sources: indirect lightning, switching transients from the grid, and surges created inside the building by motors, air conditioning compressors and other inductive loads.

BS 7671:2018+A2:2022 (Section 443) requires protection against transient overvoltages to be considered on every installation. In practice a Type 2 SPD is now specified as standard on new and replacement consumer units. See Do I need surge protection? for how the risk assessment works.

The WCED WSPD range provides Type 2 SPDs in 2-pole, 3-pole and 4-pole versions at 40kA (Imax), for single-phase and three-phase installations.

Type 1+2 combined: when does it make sense?

A Type 1+2 SPD gives both levels of protection in one unit, fitted at the consumer unit position. It is the right choice when:

  • the building has an external lightning protection system that needs Type 1
  • the supply is on overhead cables, which raises direct-strike risk
  • you want to future-proof against a lightning protection system being added later
  • space is tight and one combined device is more practical than two

The WCED WSPDTE series provides Type 1+2 SPDs in 2-pole (2-module) and 4-pole (4-module) versions.

Which type do I need?

Building or situation SPD required
Standard home, underground supply, no LPS Type 2 at the consumer unit
Building with a lightning protection system Type 1+2 combined, or Type 1 at origin plus Type 2 at the consumer unit
Overhead supply cables (rural or older networks) Type 1+2 combined at the consumer unit
Commercial site with sensitive electronics Type 2 at the main board plus Type 3 at sensitive equipment
Solar PV installation AC Type 2 at the inverter output plus DC Type 2 at the string combiner
EV charging circuit Type 2 at the consumer unit or EV distribution board

Shop WCED surge protection devices

Type 2 SPDs (2-pole, 3-pole, 4-pole) and Type 1+2 combined units, all 40kA. In stock with next working day dispatch.

View the SPD range

Frequently asked questions

Do I need a Type 1 SPD if there is no lightning protection system?

Generally no. For a standard home with underground supply cables and no external LPS, a Type 2 SPD at the consumer unit is the correct and sufficient specification. Type 1 is only needed where there is a direct-strike risk via the supply cables or an installed LPS.

What is the difference between Iimp and Imax?

Iimp (impulse current) is the rating for Type 1 SPDs: the ability to handle the high-energy, short-duration surge from a direct lightning strike. Imax (maximum discharge current) is the rating for Type 2 devices: the largest surge current they can handle without damage. They are measured with different waveforms and are not directly comparable.

Can I install a Type 2 SPD without a Type 1?

Yes. In most UK homes and light commercial installs, a Type 2 at the consumer unit is the correct and complete specification. A Type 1 is only added where direct-strike risk exists.

What is the BS number for a Type 2 SPD?

Type 2 SPDs are covered by BS EN 61643-11, the product standard manufacturers test and certify against. BS 7671 is the separate wiring regulation that says when an SPD should be fitted. The two numbers cover different things, which is a common source of confusion.

Is BS EN 61643-11 the same for Type 1, Type 2 and Type 1+2?

Yes. BS EN 61643-11 covers all three. The type classification describes the surge waveform and the location in the installation, not a separate standard.

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