Surge Protection Device Selection Guide for Electrical Engineers and Buyers

Introduction

Selecting a Surge Protection Device (SPD) is not simply a matter of choosing the highest surge current rating. The right SPD depends on four things: the electrical system, installation location, surge level, and equipment sensitivity.

For electrical engineers and B2B buyers, the correct SPD selection usually starts with five questions:

1. Where will the SPD be installed?
   Main incoming supply, distribution board, or near sensitive equipment?

2. What type of electrical system needs protection?
   AC power system, DC system, photovoltaic system, or industrial equipment?

3. Which SPD type is required?
   Type 1, Type 2, Type 3, or combined Type 1+2 protection?

4. Do the technical parameters match the application?
   Including maximum continuous operating voltage (Uc), voltage protection level (Up), and discharge current capability.

5. Does the SPD comply with the required standards?
   Such as IEC 61643-11 for AC surge protective devices or IEC 61643-31 for photovoltaic applications.

In practice, incorrect SPD selection may cause insufficient protection, higher project costs, or poor coordination with the electrical system. A properly selected SPD provides a safe path for surge current. It helps reduce the risk of damage to connected equipment.

This guide explains the key selection criteria from an engineering and procurement perspective, helping buyers and designers evaluate SPD solutions based on technical requirements rather than only product price or surge current ratings.

How to Select the Right SPD: A Practical Decision Framework

In practice, SPD selection usually follows the same steps as electrical system design.

When selecting an SPD, start with the protection requirements of the electrical system rather than choosing a product directly from a catalog.

The basic decision process is:

Electrical system → Installation location → Required SPD type → Technical parameters → Compliance verification

The following framework can be used for most low-voltage electrical applications.

Step 1: Identify the Electrical System Before Selecting an SPD

The first step in SPD selection is understanding the protected system.

Different systems have different voltage characteristics and surge risks.

For example:

• A building distribution system may require AC surge protection.

• A photovoltaic installation requires DC SPD protection designed for PV voltage conditions.

• Industrial facilities may require higher surge capacity because of motors, switching operations, and large electrical loads.

The SPD voltage rating must always be compatible with the system voltage.

Choosing an SPD with unsuitable voltage characteristics may reduce protection reliability or cause unnecessary operation of the device.

Step 2: Determine the SPD Installation Location

SPD type selection starts with one basic question: where will the device be installed?

A common mistake in SPD purchasing is selecting a device only by surge current rating while ignoring where the device will be installed.

Typical installation locations include:

The installation position should be considered together with the building's lightning protection system, grounding arrangement, and equipment protection requirements.

For a detailed comparison between Type 1 and Type 2 protection approaches, engineers can also refer to our guide on "comparison between Type 1 and Type 2 surge protection devices".

Understanding Different Types of Surge Protection Devices

SPD classification is mainly related to the location of installation and the type of surge current the device is designed to handle.

The main categories used in low-voltage systems are:

• Type 1 SPD

• Type 2 SPD

• Type 3 SPD

• Type 1+2 SPD

Type 1 SPD: Protection Against External Lightning Current

Type 1 SPD is generally installed at the incoming power supply side of a building or facility.

Its main purpose is to handle surge currents caused by direct or partial lightning effects entering the electrical installation.

The key parameter for Type 1 SPD selection is:

Iimp (impulse discharge current)

TIimp shows how much impulse current a Type 1 SPD can handle during a lightning current test, typically tested with a 10/350 μs waveform according to IEC requirements.

For example, YQNT Type 1 SPD products are designed for applications requiring high impulse current capability. The LDSP1-A25 series includes:

These parameters should be evaluated according to the actual lightning protection requirements of the project rather than selected only by current rating.

Type 2 SPD: Protection for Distribution Systems

Type 2 SPD is commonly installed in distribution boards and electrical panels.

Its role is to protect downstream electrical equipment from transient overvoltages caused by:

• switching operations

• inductive loads

• residual surge energy after upstream protection

The main selection parameters for Type 2 SPD include:

• Uc

• Up

• In

• Imax

For example, a Type 2 SPD designed for a low-voltage distribution system may require:

When selecting Type 2 protection, it is also useful to understand how the SPD works and where it is normally applied. A separate explanation is available in:

[Type 2 SPD working principle and applications]

Type 1+2 SPD: Combined Protection Solution

Type 1+2 SPD combines the functions of Type 1 and Type 2 protection in one device.

It is often considered when the project requires:

• lightning current capability

• distribution-level surge protection

• simplified installation

• reduced panel space requirements

For example, YQNT Type 1+2 AC SPD solutions integrate high discharge capability with low-voltage protection requirements for low-voltage distribution systems.

The LDSP1s12.5 series provides:

The selection between Type 1, Type 2, and Type 1+2 SPD should be based on the system protection design, not simply on which product has the highest numerical rating.

What Parameters Should You Check When Selecting an SPD?

After choosing the SPD type and installation location, the next step is checking the technical parameters.

For electrical engineers and buyers, the main parameters are:

• Uc

• Up

• Iimp

• In

• Imax

These values show whether an SPD is suitable for a specific electrical system.

1. Uc: Is the SPD Voltage Rating Suitable for the System?

Uc (Maximum Continuous Operating Voltage) is the maximum voltage that an SPD can withstand continuously during normal operation.

The Uc value should match the system voltage.

A wrong Uc selection may cause:

• unnecessary SPD operation

• reduced protection performance

For example, the YQNT PV SPD model LDSP1s-PV40-DC1000 is designed for photovoltaic DC systems.

Key data:

This allows engineers to select the SPD according to the actual system voltage.

2. Up: How Well Does the SPD Protect Equipment?

Up (Voltage Protection Level) refers to the maximum residual voltage that can appear when the SPD operates.

Simply explained:

A lower Up value means the SPD can limit surge voltage more effectively.

However, selecting an SPD only by Up is not enough.

Engineers should also consider:

• SPD type

• discharge capability

• equipment sensitivity

• installation position

For example:

YQNT SPD products use MOV-based voltage limiting technology in applicable models to control residual voltage during surge events.

3. Understanding Iimp, In and Imax

Surge current parameters are often misunderstood.

They describe different test conditions and protection capabilities.

Iimp: Lightning Current Capability

Iimp is mainly used for Type 1 SPD evaluation.

It represents the ability to handle partial lightning current using a 10/350μs waveform.

Example:

YQNT LDSP1-A25:

In and Imax: Type 2 SPD Selection

For Type 2 SPD selection:

• In shows the nominal discharge current capability.

• Imax shows the maximum discharge current capability.

A higher Imax value does not always mean a better choice.

The SPD still needs to match:

• system voltage

• installation location

• required protection level

4. Check Protection Mode and System Configuration

SPD configuration should match the electrical system.

Common configurations include:

Before selecting an SPD, engineers should confirm:

• power system type

• grounding method

• protected conductors

5. Verify SPD Standards and Technical Documents

For B2B projects, technical documents are an important part of product evaluation.

Buyers and engineers usually check:

Common SPD standards include:

IEC 61643-11

For low-voltage AC surge protective devices.

IEC 61643-31

For photovoltaic DC surge protective devices.

A qualified SPD supplier should provide clear technical documents to help engineers complete product selection and project evaluation.

SPD Selection Checklist for Electrical Projects

Before selecting an SPD model, engineers can check the following points:

This checklist helps project teams compare SPD solutions based on technical requirements, not only price.

How to Select SPD Based on Different Applications?

SPD selection depends on the electrical environment.

Different applications have different surge risks and protection requirements.

Industrial Electrical Systems

Industrial systems may include:

• motors

• control cabinets

• automation equipment

• switching devices

These systems can experience transient overvoltages caused by switching operations and inductive loads.

Common considerations:

• higher surge exposure

• equipment sensitivity

• continuous operation requirements

Typical solutions may include:

• Type 2 AC SPD for distribution panels

• Type 1+2 SPD for higher exposure locations

Commercial Buildings

Commercial buildings usually require SPD protection for:

• power distribution systems

• lighting systems

• building automation equipment

Selection normally focuses on:

• correct voltage rating

• suitable protection level

• coordination between SPD and equipment

Solar PV Systems

PV systems require DC surge protection because solar installations have:

• long outdoor cable routes

• DC voltage exposure

• lightning-induced surge risks

Engineers should check:

• PV system voltage

• Ucpv rating

• IEC 61643-31 compliance

For detailed PV protection design, a dedicated guide on surge protection for solar PV systems can provide more application-specific information.

Common SPD Selection Mistakes

1. Choosing SPD Only by Imax

A common mistake is comparing products only by:

20kA, 40kA, 100kA.

But SPD selection also requires checking:

• Up

• Uc

• SPD type

• installation location

2. Selecting the Wrong SPD Type

Type 1, Type 2, and Type 1+2 are designed for different locations.

The right SPD type is determined by its installation position, not only by the current rating.

3. Ignoring Technical Documentation

For B2B projects, product information is part of the selection process.

Missing datasheets or unclear specifications can create problems during:

• project approval

• installation

• maintenance

How to Evaluate an SPD Manufacturer Before Purchasing?

For distributors, OEM customers, and project buyers, selecting the right supplier is as important as selecting the right SPD model.

A professional SPD manufacturer should provide:

For companies comparing suppliers, reviewing the manufacturer's technical capability, documentation quality, and application experience can reduce selection risks.

You can also refer to:

How to evaluate SPD manufacturers before purchasing

for a supplier comparison approach.

FAQ

Q: How do I choose the right SPD for my electrical system?

Choose an SPD based on:

• installation location

• system voltage

• SPD type

• Up value

• Iimp/In/Imax ratings

• applicable standards

Q: Should I choose a Type 1 SPD or a Type 2 SPD?

It depends on the installation position.

• Type 1 SPD is mainly used at incoming power supplies where lightning current protection is required.

• Type 2 SPD is commonly used in distribution boards for internal surge protection.

Q: What is the difference between Iimp, In, and Imax in SPD selection?

They describe different surge current capabilities.

• Iimp: lightning impulse current capability

• In: nominal discharge current

• Imax: maximum discharge current

Q: What should distributors check before purchasing SPD products?

The main parameters are:

• Uc

• Up

• Iimp/In/Imax

• SPD type

• IEC compliance

The correct combination depends on the application.

Q: What documents should I request from an SPD manufacturer?

For B2B purchasing, request:

• product datasheet

• technical specifications

• installation instructions

• compliance information

• OEM capability information if customization is required

Conclusion

A correct SPD selection requires understanding the whole electrical system.

Engineers and buyers should evaluate:

• where the SPD will be installed

• which SPD type is suitable

• whether voltage and current parameters match

• whether technical documents and standards are available

For project-based purchasing, working with an experienced SPD manufacturer can help ensure the selected product matches technical requirements and application conditions.

A complete SPD selection process should combine electrical design requirements, product specifications, and supplier capability.