SPD Types Explained – Type 1, Type 2 & Type 3
Surge Protection Devices (SPDs) are divided into different types depending on the level of surge protection they provide and where they are intended to be installed.
The main classifications are Type 1, Type 2 and Type 3 SPDs. You may also encounter combined devices such as Type 1 + Type 2 SPDs.
Understanding these differences is important when identifying or replacing an existing SPD.
What Is a Type 1 SPD?
A Type 1 SPD is designed to deal with high-energy surge currents associated with lightning.
These devices are generally installed at the origin of an electrical installation where protection against partial lightning currents is required.
Type 1 SPDs are more commonly encountered in installations where there is an external lightning protection system or where the electrical installation has been assessed as requiring this level of protection.
They provide the first stage of surge protection before additional protection further downstream.
What Is a Type 2 SPD?
A Type 2 SPD is the type most commonly encountered in domestic consumer units and many commercial distribution boards.
Type 2 SPDs protect against transient overvoltages caused by events such as switching operations, disturbances on the electricity supply network and indirect effects of lightning.
If you open a modern domestic consumer unit and see an SPD fitted alongside the protective devices, there is a good chance it will be a Type 2 SPD or a combined device incorporating Type 2 protection.
Type 2 SPDs are available from manufacturers including Wylex, Hager, Crabtree, Schneider Electric, FuseBox and Lewden.
What Is a Type 3 SPD?
A Type 3 SPD provides an additional level of protection close to sensitive electrical or electronic equipment.
Rather than replacing Type 1 or Type 2 protection, Type 3 devices are generally used as an additional stage of protection downstream.
This can provide more localised protection for particularly sensitive equipment.
What Is a Type 1 + Type 2 SPD?
Some SPDs combine Type 1 and Type 2 protection within a single device.
These are commonly described as:
- Type 1+2
- Type 1 / Type 2
- T1+T2
- Combined Type 1 and Type 2 SPD
A combined device can provide protection against the higher-energy currents associated with Type 1 requirements while also providing Type 2 surge protection.
Type 1 vs Type 2 SPD – What's the Difference?
The main difference is the type and level of transient event the device is designed to handle.
Type 1 SPD: Designed for high-energy surge currents associated with lightning and generally installed at the origin where Type 1 protection is required.
Type 2 SPD: Designed to protect against transient overvoltages and is commonly installed in domestic consumer units and commercial distribution boards.
Type 3 SPD: Provides additional protection closer to sensitive equipment and is normally used alongside upstream protection.
One type should not automatically be substituted for another simply because it physically fits.
How Can I Tell What Type of SPD I Have?
The easiest place to start is the information printed on the front or side of the existing SPD.
Look for markings such as:
T1, Type 1, T2, Type 2, T3, Type 3 or T1+T2.
You may also find information including:
- Manufacturer
- Model or part number
- Uc – maximum continuous operating voltage
- Up – voltage protection level
- In – nominal discharge current
- Imax – maximum discharge current
- Iimp – impulse discharge current, commonly associated with Type 1 devices
- Number of poles or protection modes
These specifications can be important when identifying a suitable replacement.
Can I Replace a Type 2 SPD With Any Other Type 2 SPD?
Not necessarily.
Two SPDs can both be classified as Type 2 while having different electrical specifications, connection arrangements, dimensions and manufacturer requirements.
If you are replacing an existing SPD, identifying the exact manufacturer and part number is usually the safest starting point.
Do not assume that an SPD is compatible simply because it fits on the same DIN rail or looks similar.
Choosing the Correct Replacement SPD
When identifying a replacement, check:
- Existing SPD manufacturer
- Model or part number
- SPD type
- Electrical ratings
- Number of poles/modules
- Connection arrangement
- Whether the cartridge is replaceable
- Manufacturer compatibility information
Where possible, replacing an existing SPD with the same manufacturer and model provides the simplest route to establishing compatibility.
ReCircuit Resale stocks a range of new, surplus and discontinued SPDs and electrical components from major manufacturers.
Next Guide: How to Identify the Correct Replacement SPD