Type 1 vs Type 2 SPD: Differences, Applications, and How to Choose the Right Surge Protective Device

Introduction

Surge protective devices (SPDs) are widely used in low-voltage electrical systems to reduce the impact of transient overvoltages and protect connected equipment. However, not all SPDs are designed for the same purpose.

When selecting surge protection, one common question appears frequently:

What is the difference between Type 1 SPD and Type 2 SPD, and which one is suitable for a specific application?

Although both are part of the IEC 61643 surge protection classification system, Type 1 SPD and Type 2 SPD serve different protection roles. The main differences relate to their installation location, surge withstand capability, testing waveform, and typical application scenarios.

This guide explains the key differences between Type 1 vs Type 2 SPD, including technical parameters, installation considerations, and practical selection guidance for electrical and renewable energy applications.

Type 1 SPD vs Type 2 SPD: Quick Comparison

The key point is simple: Type 1 SPD and Type 2 SPD are not competitors. They are designed for different protection zones within an electrical system.

What Is a Type 1 SPD?

A Type 1 SPD is a surge protective device designed to handle high-energy surge currents, especially partial lightning currents entering an electrical installation.

It is typically installed at the origin of the electrical system, such as the main incoming distribution point, particularly in buildings equipped with an external lightning protection system.

The main purpose of a Type 1 SPD is to reduce the impact of large surge currents before they enter the internal electrical network.

Type 1 SPD Key Parameter: Iimp

The primary parameter used for Type 1 SPD classification is:

Impulse current (Iimp)

Iimp represents the ability of the SPD to withstand impulse current under a 10/350μs waveform test.

This waveform is designed to simulate the high-energy characteristics associated with lightning current.

For applications exposed to direct lightning risks, evaluating Iimp capability is an important part of SPD selection.

What Is a Type 2 SPD?

A Type 2 SPD is a surge protective device designed to protect low-voltage electrical equipment from transient overvoltages within the distribution system.

Type 2 SPDs are commonly installed in:

• Distribution boards

• Sub-distribution panels

• Industrial electrical cabinets

• Renewable energy systems

Compared with Type 1 SPD applications, Type 2 SPDs are typically used for downstream protection against induced surges and switching-related overvoltages.

For a more detailed explanation of Type 2 SPD operation, including how surge current is diverted and voltage is limited, you can read our guide: How a Type 2 SPD Works.

Key Differences Between Type 1 and Type 2 SPD

Understanding the difference between Type 1 and Type 2 SPD requires looking beyond the product label.

The important differences are related to:

• protection purpose

• installation position

• surge waveform

• electrical parameters

1. Protection Purpose Difference

Type 1 SPD

Type 1 SPDs focus on handling high-energy surge currents, especially where lightning current may enter the electrical installation.

Typical applications include:

• Buildings with external lightning protection systems

• Main electrical service entrances

Type 2 SPD

Type 2 SPDs focus on limiting transient overvoltages inside the electrical distribution system.

Typical causes include:

• Switching operations

• Induced lightning surges

• Grid disturbances

2. Installation Location Difference

The installation position is one of the most important differences between Type 1 and Type 2 SPDs.

Type 1 SPD Installation

Usually installed:

• At the origin of installation

• Before the main distribution equipment

Its role is to provide the first level of surge protection.

Type 2 SPD Installation

Usually installed:

• Inside distribution boards

• Near sensitive electrical equipment

• In industrial control panels

Its role is to provide protection for downstream equipment.

3. Electrical Parameter Difference: Iimp vs In and Imax

This is where many general articles provide only a surface-level comparison.

From an engineering perspective, Type 1 and Type 2 SPDs are evaluated using different surge test parameters.

Type 1 SPD: Impulse Current (Iimp)

Type 1 SPDs are tested using:

10/350μs waveform

The key parameter:

Iimp (Impulse Current)

This parameter represents the SPD's ability to withstand high-energy impulse current conditions.

Type 2 SPD: In and Imax

Type 2 SPDs are tested using:

8/20μs waveform

Important parameters include:

Nominal Discharge Current (In)

In represents the discharge current capability of the SPD under repeated surge testing conditions.

Maximum Discharge Current (Imax)

Imax indicates the maximum surge current capability of the SPD under an 8/20μs waveform.

Voltage Protection Level (Up)

Up represents the residual voltage level that remains across the SPD terminals during a surge event.

A lower Up value generally indicates better voltage limitation performance for connected equipment.

Example: Type 2 DC SPD for Photovoltaic Systems

For photovoltaic applications, YQNT's LDSP1s-PV40-DC1000 is designed as a Type 2 DC SPD for PV systems.

Technical parameters include:

• SPD Type: Type 2

• Application: Photovoltaic DC systems

• Ucpv: 1000V DC

• In: 20kA, 8/20μs

• Imax: 40kA, 8/20μs

• Up: < 3.8 kV

• Protection mode: 2+0 or 3+0

• Standard: IEC/EN 61643-31

These parameters demonstrate how engineers evaluate a Type 2 SPD based on system voltage, surge capability, and protection requirements.

Type 1 vs Type 2 SPD Applications: Which One Should You Choose?

There is no universal answer that Type 1 SPD is always better or Type 2 SPD is always sufficient.

The correct choice depends on the electrical installation design and risk environment.

Application 1: Buildings With External Lightning Protection

Where a building has an external lightning protection system, Type 1 SPD may be required because the installation may experience partial lightning current.

Application 2: Commercial and Industrial Electrical Systems

For many low-voltage distribution systems, Type 2 SPDs are commonly installed in distribution boards to protect connected electrical equipment.

Application 3: Solar PV Systems

Photovoltaic systems require careful surge protection planning because they usually include:

• Outdoor installation

• Long DC cable runs

• Sensitive inverter equipment

Type 2 DC SPDs are widely used on the DC side of PV systems to protect components such as solar inverters and DC distribution equipment.

Can Type 1 and Type 2 SPDs Be Used Together?

Yes.

In many electrical installations, Type 1 and Type 2 SPDs can work together as part of a coordinated surge protection strategy.

A typical arrangement may include:

• Type 1 SPD at the incoming power side

• Type 2 SPD at downstream distribution points

The actual protection design depends on:

• installation requirements

• lightning risk assessment

• electrical system configuration

How to Choose Between Type 1 and Type 2 SPD?

When selecting between Type 1 and Type 2 SPD, engineers should consider:

1. Installation Environment

Where will the SPD be installed?

• Incoming electrical supply?

• Distribution board?

• PV DC system?

2. Surge Exposure Level

Does the installation face:

• Direct lightning exposure?

• Induced surges?

• Switching disturbances?

3. Electrical Parameters

Important specifications include:

• Iimp

• In

• Imax

• Up

• System voltage rating

4. Supplier Capability

For industrial projects and OEM requirements, evaluating the SPD manufacturer is also important.

Factors may include:

• Certification capability

• Production experience

• Technical support

• Customization ability

For a detailed guide on evaluating suppliers, you can read:

How to Compare SPD Manufacturers

FAQs About Type 1 vs Type 2 SPD

What is the main difference between Type 1 and Type 2 SPD?

The main difference is their protection purpose and installation position. Type 1 SPD is designed for high-energy surge current protection at the origin of an installation, while Type 2 SPD is used mainly for distribution-level transient overvoltage protection.

Do I need a Type 1 or Type 2 SPD?

The choice depends on the installation environment, lightning protection requirements, system design, and applicable standards.

Can a Type 2 SPD replace a Type 1 SPD?

Not always. Type 1 and Type 2 SPDs are designed for different protection levels and may be used separately or together depending on the electrical installation requirements.

What is Iimp in a Type 1 SPD?

Iimp is the impulse current rating used for Type 1 SPD testing with a 10/350μs waveform.

What are In and Imax in Type 2 SPD?

In and Imax are surge current ratings used for Type 2 SPD evaluation under an 8/20μs waveform.

Conclusion

Understanding the difference between Type 1 vs Type 2 SPD is essential when designing reliable low-voltage electrical protection systems.

Type 1 SPD and Type 2 SPD are designed for different applications:

• Type 1 SPD focuses on high-energy surge current protection at the installation origin.

• Type 2 SPD focuses on protecting downstream electrical equipment from transient overvoltages.

By evaluating installation conditions, surge exposure, and technical parameters such as Iimp, In, Imax, and Up, engineers can select a more suitable surge protection solution.

As a manufacturer of AC and DC surge protective devices, YQNT focuses on providing reliable SPD solutions for photovoltaic systems, industrial applications, and low-voltage electrical protection projects.