How to Select a Type 1+2 Surge Protection Device

Have you ever felt overwhelmed by a long list of surge protection parameters — wondering how to choose between Iimp, Uc, and Up, and worrying about selecting the wrong model, inadequate protection, or even leaving potential safety risks? When choosing a Type 1+2 Surge Protection Device, many users want a complete solution that provides both direct lightning current protection and induced surge protection, but they also worry about spending more than necessary. The following section will help you clarify your thinking and easily find a selection strategy suited to your system.

What Is a Type 1+2 Surge Protection Device?

A Type 1+2 Surge Protection Device can simply be understood as “combining two levels of protection into a single enclosure.”

According to the IEC/EN 61643-11 standard, Type 1 SPD is designed to withstand high-energy impulse currents caused by direct lightning strikes, using the 10/350 μs waveform, while Type 2 SPD is mainly used to handle transient overvoltages caused by indirect lightning effects or switching operations within the electrical system, tested with the 8/20 μs waveform.

Traditionally, these two types of SPDs are installed separately, and sufficient cable distance must be maintained between them to achieve proper energy coordination. Otherwise, both devices may operate at the same time, causing the Type 2 SPD’s MOV components to withstand energy levels beyond their intended capability, which can accelerate aging or even lead to immediate failure.

A Type 1+2 Surge Protection Device solves this issue by integrating both protection stages into a single module with internal coordination completed during the manufacturing process. During installation, there is no need to worry about whether sufficient cable length is available between separate protection devices. One device can provide protection against both lightning current surges and subsequent residual overvoltages, making it especially suitable for applications with limited space in distribution panels or installations where the service entrance is located close to the main distribution board.

When Should You Choose a Type 1+2 Surge Protection Device?

The first step in selecting a Type 1+2 Surge Protection Device is not checking the specification sheet, but identifying which application scenario your electrical system belongs to. The following situations are often where a Type 1+2 Surge Protection Device is the most suitable choice.

Buildings Equipped with an External Lightning Protection System (LPS)

If a building is equipped with an external lightning protection system, such as air terminals and down conductors, a direct lightning strike will cause the lightning current to be discharged to the ground through the down conductors. However, part of the energy can also be coupled into the building’s low-voltage distribution system through the grounding system.

In this situation, relying only on a Type 2 SPD is not sufficient, because it cannot withstand the high-energy impulse current of the 10/350 μs waveform. According to IEC 62305 requirements, buildings with external lightning protection systems should have a device with Type 1 protection capability installed at the entrance of the main distribution board.

If the distribution cabinet has limited space and cannot accommodate separate Type 1 and Type 2 SPDs, a Type 1+2 Surge Protection Device becomes a practical solution that provides both compliance and space efficiency.

High Lightning Risk Areas and Facilities

Even if a building does not have an external lightning protection system, the lightning risk may still be significant in some locations. For example, areas with frequent thunderstorms throughout the year, or open sites without tall surrounding structures for protection, are more likely to be exposed to lightning strikes.

In these situations, if overhead power lines are affected by induced lightning, the surge energy can travel directly along the lines into the electrical distribution system. A Type 2 SPD alone may provide insufficient protection when facing this level of energy impact.

Evaluating the lightning activity level of the installation area in advance is an important factor in determining whether Type 1+2 protection is required. It is better to plan proper protection beforehand rather than wait until equipment failures occur and regret not installing adequate surge protection.

Industrial and Commercial Power Distribution Systems

The sources of surges in industrial and commercial power distribution systems are often more complex than expected. Type 1+2 Surge Protection Devices are widely used in these applications, mainly because:

• There are many production machines and frequent switching operations, which can generate a large number of internal surges.
• Distribution cabinets are usually located close to the main incoming power supply, where installation space is often limited.
• Once surge protection fails, the cost of production downtime or data loss can be extremely high.

Whether installed in the main distribution cabinet of a factory or the electrical room of a commercial building, users typically want to minimize downtime and maintenance costs as much as possible. A Type 1+2 SPD can handle both external lightning surges and internal switching surges, while also reducing wiring complexity and saving cabinet space compared with installing separate Type 1 and Type 2 SPDs.

Photovoltaic Systems, EV Charging Systems, and Critical Infrastructure

Photovoltaic power plants and EV charging stations share a common challenge: their equipment is highly sensitive to voltage fluctuations, and many installations are located outdoors, directly exposed to lightning risks. Once inverters or charging modules are damaged by surges, repair costs and downtime losses can be significant.

The same applies to critical infrastructure such as data centers and water treatment plants. A single unexpected outage may affect not only the equipment itself but also the entire business operation chain. These applications require a high level of operational continuity. Installing a Type 1+2 Surge Protection Device at the main power distribution entrance can help address both lightning surges and internal switching surges, reducing the risk of major losses caused by unexpected failures.

How to Select the Right Type 1+2 Surge Protection Device for Your Electrical System?

Once the application scenario has been identified, the actual selection process begins. The following six factors provide a practical step-by-step approach to selecting the right Type 1+2 Surge Protection Device, from installation location to specific technical parameters.

Select Based on Installation Location and Lightning Protection Zone (LPZ)

The starting point of selection is to first determine which protection zone boundary the device will be installed at. According to the IEC 62305 classification, the external area of a building is defined as LPZ 0A/0B, while the main distribution board is typically located at LPZ 1. Moving further downstream to LPZ 2 and LPZ 3, the surge energy is progressively reduced.

A Type 1+2 Surge Protection Device is usually installed at the boundary between LPZ 0 and LPZ 1, such as the service entrance or main distribution board. This location is where lightning current and induced surge energy first enter the electrical system. If your SPD is intended to be installed at this point, a Type 1+2 solution is generally the appropriate choice.

However, for downstream sub-distribution boards, a standalone Type 2 SPD is often sufficient, and there is usually no need for over-specification. Always determine the installation location first before selecting the parameters — the order matters.

Select Based on the Earthing System (TN, TT, or IT)

The type of earthing system directly determines how the SPD should be wired and how many poles are required. This step is often overlooked, but choosing the wrong configuration can significantly reduce the protection performance. Common scenarios include:

• TN-S system: The neutral conductor and protective earth (PE) conductor are separated throughout the system. A 4-pole device (3L+N with separate connection to PE) is typically required.
• TN-C-S / TT system: A 3+1 configuration is generally used, with an additional GDT module installed between N and PE to handle different fault conditions.
• TN-C system: The neutral conductor and protective conductor are combined as PEN, so only an L-PEN connection can be used. A separate N-PE connection must not be installed.
• IT system: The system has no direct connection to earth or is connected through high impedance, which requires a significantly higher Uc withstand capability.

Therefore, before selecting an SPD, always confirm the earthing system used in the project location and then choose the appropriate number of poles and wiring configuration based on the product specifications. This is often more important than simply looking at the kA rating.

Select the Appropriate System Voltage and Maximum Continuous Operating Voltage (Uc)

The Uc parameter refers to the maximum voltage that an SPD can continuously withstand under normal operating conditions. It must have sufficient margin above the system’s rated phase voltage; otherwise, the device may operate incorrectly or experience premature aging even without any surge events.

According to the general requirements of IEC 61643-11, Uc should not be lower than 1.1 times the nominal system voltage. For example, in a standard 230/400V three-phase system, a Uc rating of 275V is typically the minimum choice. However, for TT earthing systems, the neutral point voltage may temporarily rise during fault conditions, so a higher Uc margin is often required, such as 320V.

Therefore, SPD selection should not be based only on whether the voltage rating matches the system. The earthing system must also be considered at the same time. These two factors are closely related, and evaluating either one separately can easily lead to incorrect selection.

Determine the Required Impulse Discharge Current (Iimp)

Iimp is the parameter that best reflects the lightning current withstand capability of a Type 1+2 Surge Protection Device. Measured in kA, it corresponds to the 10/350 μs waveform. The required value mainly depends on the building’s Lightning Protection Level (LPL).

If a formal lightning risk assessment has been carried out, buildings with higher protection levels such as LPL I and LPL II typically require an Iimp of at least 25 kA per pole. For standard commercial and residential buildings with LPL III and LPL IV, 12.5 kA is generally sufficient.

If no risk assessment has been performed, a common industry practice is to use 12.5 kA as the minimum reference value, while areas with frequent lightning activity are recommended to choose a 25 kA rating directly. Selecting an Iimp value that is too low may result in the SPD being unable to effectively handle the energy of a real direct lightning strike.

Evaluate the Nominal Discharge Current (In) and Maximum Discharge Current (Imax)

If Iimp represents the “big event” of a direct lightning strike, then In and Imax deal with the surge energy that occurs more frequently in daily operation. Both parameters are based on the 8/20 μs waveform:

• In (Nominal Discharge Current): The discharge current level that the SPD can withstand repeatedly without performance degradation, representing long-term reliability.
• Imax (Maximum Discharge Current): The highest single surge current the SPD can withstand, representing the safety limit under extreme conditions.

Generally, an In rating of at least 20 kA is considered an acceptable baseline, while higher values provide greater safety margins. However, these two parameters are not simply a case of “the higher, the better.” Higher ratings do not always mean better value or suitability. The key is to match the SPD with the actual surge frequency and intensity expected in your system.

During selection, you should compare the product specifications item by item rather than making a decision based on a single parameter.

Select the Appropriate Voltage Protection Level (Up)

Up determines how low the residual voltage can be limited when a surge occurs. This value must be lower than the withstand voltage level of downstream equipment; otherwise, even if the SPD operates correctly, the equipment may still be damaged.

According to the overvoltage category classification in IEC 60664-1, common electronic devices and household appliances typically have a withstand voltage of around 2.5 kV. In such cases, selecting an SPD with an Up value below 2.5 kV is generally sufficient.

However, if the downstream equipment includes sensitive electronic devices or data-related equipment, the withstand voltage level is often only around 1.5 kV. In these situations, an SPD with a lower Up value should be selected, or an additional Type 2/Type 3 SPD should be installed downstream for further protection.

Common Mistakes When Selecting a Type 1+2 Surge Protection Device

Understanding all the parameters does not necessarily mean you will avoid selection mistakes. The following issues are some of the most easily overlooked yet potentially critical mistakes that often occur in real-world projects.

Focusing Only on the kA Rating While Ignoring Overall Performance

Many people’s first reaction when selecting an SPD is that “the higher the kA rating, the better.” They place an order simply after seeing a higher number on the specification sheet, while equally important parameters such as Up and Uc may not actually match the system requirements.

In reality, a higher value for a single parameter does not necessarily mean better overall protection performance. If the Up value is too high, downstream equipment can still be damaged. SPD selection is not about comparing one number — it requires matching multiple parameters together to achieve effective protection.

Ignoring the Differences in Selection Requirements Caused by the Earthing System

The TN, TT, and IT earthing systems require completely different pole configurations and wiring methods. However, many people take shortcuts by directly copying the SPD model used in another project. As a result, the protection mode may be incorrect after installation, or the N-PE connection may not be suitable for that specific system.

Once the earthing system is overlooked, even the most accurate parameter selection afterward will not solve the problem. It must always be confirmed correctly at the beginning of the selection process.

Incorrect Selection of the Maximum Continuous Operating Voltage (Uc)

If the Uc value is selected too low, the SPD may frequently operate incorrectly under normal operating voltage conditions, or even experience premature aging and failure. Choosing a Uc value that is only at the edge of the nominal voltage range can also cause problems when the grid voltage fluctuates.

This is especially important in TT systems, where the neutral point voltage may temporarily rise during fault conditions. Without sufficient voltage margin, a Uc rating that appears to be “adequate” may actually leave insufficient safety headroom.

Ignoring the Coordination Between the Backup Protection Device and the SPD

The SPD itself also requires a backup protection device, such as a circuit breaker or fuse. If an internal SPD fault occurs, this protection device must be able to disconnect the circuit quickly; otherwise, there may be a risk of fire.

In some projects, this step is skipped for convenience, or an unsuitable backup protection device is selected. When a fault actually occurs, it may be discovered that the backup protection rating does not match the SPD specifications or the system short-circuit current requirements.

Incorrect Installation Location Selection

The primary purpose of a Type 1+2 SPD is to be installed at the service entrance or main distribution board, which is typically the LPZ 0/1 boundary. If it is installed in a downstream distribution board, it is not only an unnecessary over-configuration, but more importantly, it fails to block the most dangerous direct lightning energy at the source.

In other words, the protection effort is wasted at the wrong location, while the critical first line of defense that should handle high-energy lightning currents may still be missing.

How Do IEC and EN Standards Affect the Selection of Type 1+2 Surge Protection Devices?

All the parameters and selection principles discussed above are not arbitrary — they are based on two core standards: IEC/EN 61643-11 and IEC 62305.

IEC/EN 61643-11 defines how SPDs should be tested and specifies their performance requirements, while IEC 62305 provides guidance on how the overall lightning protection system of a building should be designed and where SPDs should be installed.

In simple terms, one standard focuses on whether the device meets the required performance criteria, while the other focuses on whether the SPD is installed in the correct location within the protection system. When selecting a Type 1+2 Surge Protection Device, these two standards should be considered together to ensure both equipment performance and system protection requirements are properly addressed.

Performance Requirements for Surge Protection Devices According to IEC/EN 61643-11

This standard sets the “qualification baseline” for Type 1+2 Surge Protection Devices. It specifies the tests that must be passed before a product can be recognized as a genuine Type 1+2 SPD.

Test Item	Corresponding Waveform	Verification Purpose
Class I (Type 1) Test	10/350 µs	Verifies whether the SPD can withstand the declared Iimp impulse current
Class II (Type 2) Test	8/20 µs	Verifies whether In can withstand 15 repeated surge impulses and whether Imax meets the required level
Voltage Protection Level Test	8/20 µs	Confirms whether the Up value remains within the specified range
Aging and Thermal Stability Test	—	Verifies whether MOV performance remains stable during long-term operation

Only after passing all of these tests can a product datasheet legitimately include both sets of parameters: Iimp and In/Imax. Missing any one of these requirements means it cannot be considered a true Type 1+2 Surge Protection Device.

Guidance on SPD Configuration According to the IEC 62305 Lightning Protection Standard

While IEC 61643-11 focuses on whether the SPD itself meets the required performance standards, IEC 62305 focuses on how the overall lightning protection system should be designed and implemented.

It divides buildings into different Lightning Protection Zones (LPZ 0A, 0B, 1, 2, and 3), defines what level of protection should be installed at each boundary, and provides the basis for determining whether a building requires an external lightning protection system and what Lightning Protection Level (LPL) is needed.

The decision mentioned earlier — whether the required Iimp should be 12.5 kA or 25 kA — is essentially derived from the LPL classification defined in IEC 62305. These two standards are intended to be used together; relying on only one of them may result in an incomplete SPD selection.

Frequently Asked Questions

Can a Type 1+2 SPD Replace Separate Type 1 and Type 2 SPDs?

Yes, a Type 1+2 SPD can replace separate Type 1 and Type 2 devices. It integrates the high discharge capacity for direct lightning (10/350 μs) and the low voltage protection level for induced surges (8/20 μs) into one unit. This combined functionality makes it ideal for main distribution boards, saving space and reducing costs while ensuring reliable protection for connected equipment.

Does a Residential Distribution Board Need a Type 1+2 SPD?

A Type 1+2 SPD is recommended for residential panels if the building has an external lightning protection system or is supplied by overhead lines. It provides comprehensive protection against both direct lightning strikes and switching surges. Using this combined device saves space in compact distribution boxes while ensuring superior safety for sensitive modern home electronics.

How to Choose a 1P, 2P, 3P, or 4P Type 1+2 Surge Protection Device?

Selection depends on your earthing system. Use 1P or 2P for single-phase (1P for TN-C, 2P for TN-S/TT). For three-phase systems, choose 3P for TN-C or 4P for TN-S and TT networks. This ensures all active lines, including the neutral, are protected against the ground. Correct pole configuration is essential for maximizing safety and meeting IEC standards in various residential or industrial grids.

How Many kA Should You Choose for a Type 1+2 SPD?

The kA rating depends on the Lightning Protection Level (LPL). For Type 1+2 SPDs, focus on the impulse current (Iimp). Usually, 12.5 kA per pole is sufficient for standard buildings, while 25 kA is used for high-risk sites. Ensure the chosen rating matches your site’s risk assessment and local standards to safely handle expected surge energy from direct lightning and switching operations.

Is a Type 1+2 SPD Suitable for Three-Phase Systems?

Yes, Type 1+2 SPDs are perfectly suitable for three-phase systems. They are typically available in 3P configurations for TN-C networks and 4P configurations for TN-S or TT networks. By protecting all three phases and the neutral, these devices safeguard industrial and commercial equipment against both direct lightning strikes and switching surges in a single, space-saving unit.

Can One Type 1+2 SPD Protect an Entire Building?

A Type 1+2 SPD at the main board provides primary defense against lightning and surges. However, it may not be enough for large buildings. Because the protection radius is limited (usually 10 meters), sensitive equipment far from the main panel needs additional Type 2 or 3 SPDs. One unit protects the entry point, but a multi-level approach is best for total building safety.

How Often Should a Type 1+2 SPD Be Replaced?

Type 1+2 SPDs do not have a fixed expiration date. Their lifespan depends on the frequency and intensity of the surges they absorb. You must replace the unit when the visual status indicator turns from green to red. Additionally, regular annual inspections or checks after major lightning storms are recommended to ensure the device is still functional and protecting your electrical system.

Can a Type 1+2 SPD Be Added If a Separate Type 1 SPD Is Already Installed in the Panel?

Adding a Type 1+2 SPD alongside an existing Type 1 in the same panel is not recommended due to redundancy and potential device coordination issues. If Type 1 is already installed, you should simply add a standalone Type 2 SPD to handle switching surges. Alternatively, remove the old unit and completely replace it with the Type 1+2 SPD for unified protection.