What Is a Type 2 SPD and How Does It Work

Introduction

Electrical systems today are surrounded by sensitive equipment — from solar inverters and industrial controllers to distribution panels and automation systems. While these devices are designed to operate reliably, they can still be affected by sudden voltage spikes caused by lightning-induced surges, switching operations, or disturbances in the power network.

A Type 2 SPD (Surge Protective Device) is designed to reduce the impact of these transient overvoltages by safely diverting surge current and limiting the voltage that reaches connected equipment.

Unlike traditional circuit protection devices that mainly deal with overload and short-circuit conditions, a Type 2 surge protective device focuses on transient overvoltage protection.

In this guide, we will explain what a Type 2 SPD is, how a Type 2 SPD works, where it is installed, and the key electrical parameters engineers should understand before selecting a surge protection device.

What Is a Type 2 SPD?

A Type 2 SPD is a surge protective device designed for installation in low-voltage electrical distribution systems, typically inside distribution boards, sub-distribution panels, and electrical control cabinets.

Its primary function is to protect electrical equipment from transient overvoltages caused by:

• Indirect lightning effects

• Electrical switching operations

• Grid disturbances

• Sudden voltage fluctuations

A Type 2 SPD works by providing a controlled path for surge current when an abnormal voltage event occurs. Instead of allowing excessive voltage to reach downstream equipment, the SPD limits the surge and helps maintain a safer voltage level for connected devices.

In practical applications, Type 2 SPDs are commonly installed close to the equipment they protect, such as:

• Industrial control systems

• Commercial electrical panels

• Building distribution boards

• Renewable energy systems

• Photovoltaic installations

Type 2 SPD vs Traditional Electrical Protection Devices

It is important to understand that a surge protective device is not a replacement for a circuit breaker or fuse.

Different devices solve different electrical problems:

For example, an MCB may disconnect a circuit during excessive current, but it does not limit a short-duration voltage surge caused by lightning or switching events.

This is why modern electrical systems often combine:

• Circuit protection

• Surge protection

• Switching components

to create a complete low-voltage protection solution.

How Does a Type 2 SPD Work?

The working principle of a Type 2 surge protective device is based on controlling transient voltage and safely discharging surge current.

Most Type 2 SPDs use voltage-limiting components such as metal oxide varistors (MOVs).

The protection process can be explained in four steps.

1. Normal Operating Condition

Under normal voltage conditions, the SPD remains in a high-resistance state.

The electrical system operates normally, and the SPD does not interfere with power delivery.

2. Surge Event Occurs

When a transient overvoltage appears, such as a lightning-induced surge or switching spike, the voltage across the SPD increases rapidly.

At this moment, the SPD detects that the voltage has exceeded its designed operating range.

3. Surge Current Discharge

The internal MOV protection element changes its electrical characteristics and creates a low-impedance path for the surge current.

The excessive surge energy is redirected safely through the protection path.

4. Voltage Limiting

While diverting surge current, the SPD limits the remaining voltage level, known as the voltage protection level (Up).

This helps reduce stress on connected electrical equipment.

After the surge event disappears, the SPD returns to its normal high-resistance condition and remains ready for future protection events.

Where Are Type 2 SPDs Used?

The application of a Type 2 SPD depends on the electrical system design and protection requirements.

Common installation locations include:

Distribution Boards and Electrical Panels

Type 2 SPDs are widely used in low-voltage distribution systems to protect downstream electrical equipment.

Typical applications include:

• Commercial buildings

• Industrial facilities

• Control panels

• Machinery cabinets

Industrial Control Systems

Modern industrial environments contain many sensitive electronic components, including:

• PLC systems

• Controllers

• Power supplies

• Communication modules

Transient voltage events may cause equipment malfunction or unexpected downtime.

A properly selected Type 2 SPD helps improve system reliability by reducing transient overvoltage exposure.

Solar PV Systems

Photovoltaic systems are another important application area for Type 2 surge protection.

Solar installations often include:

• Long DC cable runs

• Outdoor equipment

• Solar inverters

• Combiner boxes

These conditions can increase exposure to induced surge voltages.

For photovoltaic systems, a Type 2 DC SPD is commonly installed on the DC side to protect solar inverters and related DC equipment.

For example, YQNT's LDSP1s-PV40-DC1000 Type 2 DC SPD is designed for photovoltaic applications with:

• Ucpv: 1000V DC

• Nominal discharge current (In): 20kA, 8/20μs

• Maximum discharge current (Imax): 40kA, 8/20μs

• Voltage protection level (Up): < 3.8 kV

• Protection mode: 2+0 or 3+0

These parameters help engineers match the SPD with the requirements of a specific PV system.

Key Parameters of a Type 2 SPD: In, Imax, Up, and Uc Explained

Selecting a Type 2 SPD is not only about choosing a higher discharge current rating.

Engineers usually evaluate several electrical parameters together, including operating voltage, discharge capability, and voltage protection level.

Understanding these specifications makes it easier to select the correct surge protective device for a specific application.

1. Maximum Continuous Operating Voltage (Uc / Ucpv)

The maximum continuous operating voltage (Uc) represents the highest voltage that an AC SPD can continuously withstand during normal operation.

For photovoltaic DC applications, this parameter is usually expressed as Ucpv.

The selected voltage rating should match the actual system voltage.

For example:

A photovoltaic system operating at 1000V DC requires a DC SPD with a suitable Ucpv rating.

YQNT LDSP1s-PV40-DC1000:

• Ucpv: 1000V DC

This specification ensures the SPD can operate safely within the PV system voltage range.

2. Nominal Discharge Current (In)

The nominal discharge current (In) indicates the surge current that the SPD can discharge repeatedly under an 8/20μs waveform test.

It is one of the important indicators used to evaluate SPD performance.

For LDSP1s-PV40-DC1000:

• In: 20kA

• Test waveform: 8/20μs

A higher In rating generally indicates stronger repeated surge discharge capability.

However, the correct value should always be considered together with:

• Installation environment

• Expected surge exposure

• System requirements

3. Maximum Discharge Current (Imax)

The maximum discharge current (Imax) represents the highest surge current capability of the SPD under an 8/20μs waveform.

It describes the maximum surge current that the SPD can handle during a severe transient event.

For YQNT LDSP1s-PV40-DC1000:

• Imax: 40kA

• Waveform: 8/20μs

When selecting a Type 2 SPD, engineers should not look at Imax alone. The protection level, voltage rating, and application environment are also important.

4. Voltage Protection Level (Up)

The voltage protection level (Up) represents the residual voltage that appears across the SPD terminals during a surge event.

A lower Up value generally means better voltage limitation performance.

For sensitive electrical equipment, Up is an important parameter because excessive residual voltage may damage downstream components.

For LDSP1s-PV40-DC1000:

• Up: < 3.8 kV

This value helps engineers evaluate whether the SPD provides suitable protection for the connected PV equipment.

5. Protection Mode and Installation Configuration

Type 2 SPDs can have different protection configurations depending on the electrical system design.

Common configurations include:

• 2+0

• 3+0

• 1+1

• 3+1

The correct configuration depends on:

• System wiring arrangement

• Grounding method

• Protection requirements

For photovoltaic DC systems, selecting the correct protection mode is important because an incorrect configuration may reduce the effectiveness of surge protection.

Type 2 SPD Standards and Testing

Reliable surge protective devices are tested according to international standards.

For low-voltage surge protective devices, one important standard is:

IEC 61643-11

This standard defines testing requirements related to:

• Surge current capability

• Voltage protection level

• Safety performance

For photovoltaic applications, DC surge protective devices are commonly evaluated according to photovoltaic-specific requirements such as:

IEC/EN 61643-31

YQNT photovoltaic SPD products are designed according to relevant international standards to support global electrical protection applications.

How to Select a Type 2 SPD?

When selecting a Type 2 SPD, engineers should consider:

1. System Voltage

Confirm the AC voltage or PV DC voltage level.

Examples:

• 230V AC system

• 600V DC PV system

• 1000V DC PV system

2. Protection Requirements

Evaluate:

• Expected surge exposure

• Equipment sensitivity

• Installation location

3. SPD Electrical Parameters

Check:

• Uc / Ucpv

• In

• Imax

• Up

• Protection mode

4. Supplier Capability

For industrial projects and OEM requirements, technical capability and manufacturing experience also matter.

When comparing different surge protection device suppliers, buyers should evaluate factors such as product testing, certification, technical support, production capability, and customization experience.

You can also read:

How to Compare SPD Manufacturers: A Practical Guide for Electrical Buyers

to understand the key factors when evaluating SPD suppliers.

FAQs About Type 2 SPD

What is a Type 2 SPD used for?

A Type 2 SPD is used to protect low-voltage electrical systems and connected equipment from transient overvoltages caused by lightning-induced surges and switching events.

How does a Type 2 surge protective device work?

A Type 2 SPD works by detecting excessive voltage, diverting surge current through internal protection components such as MOVs, and limiting the remaining voltage level.

Where should a Type 2 SPD be installed?

Type 2 SPDs are commonly installed in distribution boards, electrical panels, industrial control cabinets, and renewable energy systems.

What parameters are important when selecting a Type 2 SPD?

Important parameters include:

• Uc or Ucpv

• In

• Imax

• Up

• Protection configuration

These specifications determine whether the SPD matches the electrical system requirements.

Can a Type 2 SPD be used in solar PV systems?

Yes. Type 2 DC SPDs are commonly used on the DC side of photovoltaic systems to protect solar inverters and DC electrical equipment from transient overvoltages.

Conclusion

A Type 2 SPD is an important component in modern low-voltage electrical protection systems, helping reduce the impact of transient overvoltages caused by lightning-induced surges and switching events.

Understanding how a Type 2 SPD works and how to evaluate key parameters such as Ucpv, In, Imax and Up allows engineers and system designers to select more suitable surge protection solutions.

For photovoltaic, industrial, and commercial applications, choosing the correct SPD configuration and technical specifications is essential for building safer and more reliable electrical systems.

YQNT provides AC and DC surge protective devices, including photovoltaic DC SPDs, designed for renewable energy systems, industrial applications and low-voltage power distribution projects.