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

Surge Protection Devices (SPDs) come in three categories based on where in the installation they are installed and what magnitude of surge they are designed to handle. Most UK domestic and commercial installations need a Type 2 SPD at the consumer unit as a minimum.

Electrical surges — brief overvoltage transients caused by lightning, grid switching, or large motor loads — are one of the most common causes of electronic equipment failure and a contributing factor in electrical fires. SPDs protect against these events by diverting excess voltage safely to earth before it can damage connected equipment or wiring.

The three SPD categories define where in the supply chain they are installed, not simply how powerful they are. Understanding the difference is essential for correct specification under BS 7671:2018 Amendment 2.

The three SPD categories

Type	Location	Impulse rating	Protects against	Standard
Type 1	Origin of installation — main incomer, before 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 / distribution board	5–40 kA (Imax)	Indirect lightning surges and switching transients from the grid or within the building	BS EN 61643-11
Type 3	Point of use — at 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 required when a building has a lightning protection system (LPS) installed, when overhead supply cables are used (rather than underground cables), or when the installation is at elevated risk of direct lightning strike — typically isolated buildings, tall structures, or buildings in areas of high lightning ground flash density. For most standard UK domestic properties with underground DNO supply cables, Type 1 is not required unless a lightning protection system is present.

Type 1 devices must be installed upstream of the consumer unit, typically at the service head or meter position, by arrangement with the DNO. They require a direct earth connection and often a coordinated backup overcurrent device.

Type 2 — the standard for UK domestic and commercial

Type 2 SPDs are installed at the consumer unit or distribution board and protect against the most common surge sources: indirect lightning, switching transients from the grid, and surges generated internally by motors, air conditioning compressors, and other inductive loads switching on and off.

Under BS 7671:2018 Amendment 2, a Type 2 SPD is now required at all consumer units in new residential buildings in England (Building Regulations Part P) and is strongly recommended for all other domestic and commercial installations. A risk assessment is technically required, but in practice most competent installers specify one as standard given the low cost relative to the protection provided.

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

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

A Type 1+2 combined SPD provides both Type 1 and Type 2 protection in a single unit, installed at the consumer unit position. This is the appropriate specification when:

A building has an external LPS (lightning protection system) requiring Type 1
Overhead supply cables are used, increasing direct strike risk
The installer wants to future-proof the installation against a possible LPS addition
Space is limited and a combined device is more practical than two separate units

The WCED WSPDTE series provides Type 1+2 combined SPDs in 2-pole (2-module) and 4-pole (4-module) configurations. These are the correct specification for installations requiring both protection levels in a single device.

Which type do I need?

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

Shop WCED Surge Protection Devices

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

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Frequently Asked Questions

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

Generally no — for standard domestic buildings 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 required when there is a direct risk of lightning strike via the supply cables or an installed LPS that introduces the possibility of large surge currents at the installation origin.

What is the difference between Iimp and Imax ratings?

Iimp (impulse current) is the rating used for Type 1 SPDs — it represents the device's ability to handle the high-energy, short-duration surges from a direct lightning strike. Imax (maximum discharge current) is used for Type 2 devices — it represents the maximum surge current the device can handle without damage. The two values are measured using different waveforms and are not directly comparable.

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

Yes — in the majority of UK domestic installations, a Type 2 at the consumer unit is the correct and complete specification. A Type 1 is only needed when direct strike risk via the supply cables or structure exists. Installing a Type 2 without a Type 1 is perfectly compliant and standard practice in most UK domestic and light commercial installations.

Further reading:
Do I need surge protection? 18th Edition guide
SPD for EV chargers
SPD kA rating explained (40kA)
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