How to choose the right surge protection device (SPD): complete selection guide

 

Choosing a surge protection device (SPD) isn't simply about picking the highest kA rating. The correct selection depends on the electrical system, installation point, expected surge exposure and equipment being protected. IEC 61643-11:2025 sets requirements for low-voltage AC SPDs, including performance, safety and testing.

 

In simple terms, the right SPD depends on where it will be installed and what it needs to protect. For many distribution-board applications, a surge protection device Type 2 is commonly used, while Type 1, Type 1+2 and Type 3 devices may be needed at other points in the system.

Start with the protection point

SPD type	Where it is used	Main purpose
Type 1	Main incoming supply	Handles high-energy surges, including lightning-related exposure
Type 1+2	Main distribution point	Combines Type 1 and Type 2 protection
Type 2	Distribution boards	Limits surge voltages reaching downstream equipment
Type 3	Close to sensitive equipment	Adds protection for sensitive electronic devices

 

The table gives you the basic picture. Type 1 is used closer to the incoming supply, Type 2 is commonly used at distribution boards, and Type 3 provides additional protection close to sensitive equipment.

 

First identify where the device will be installed. Type 1 SPDs address higher-energy lightning exposure, while Type 2 devices are commonly used at distribution boards to limit overvoltages reaching downstream circuits. Type 1+2 combines both protection functions.

 

For many distribution-board applications, a surge protection device type 2 is the practical choice. Type 2 SPDs are tested with an 8/20 μs current waveform and are designed to discharge a surge current while limiting the voltage applied to connected equipment.

Do not choose by kA alone

Check the SPD's core electrical ratings against the actual installation. Uc, or maximum continuous operating voltage, must match the system voltage and earthing arrangement.

 

Up, or voltage protection level, indicates the voltage level limited across the SPD terminals during the specified test condition. It should remain suitable for the protected equipment's withstand capability. In, or nominal discharge current, indicates the rated surge current for the specified test. Imax, or maximum discharge current, shows the device's higher surge-handling capability.

 

A surge protection device Type 2 should therefore be selected using its complete rating information, not one headline number.

Match the SPD to the installation

System configuration matters. Confirm whether the application is single-phase or three-phase, identify the required protection modes, and check the installation and upstream protection requirements. Axis provides Type 1, Type 1+2 and Type 2 options for both single- and three-phase applications.

 

Connection details matter too. Keep SPD connecting conductors as short as practical. Longer wiring can reduce the SPD's effectiveness during a fast surge. Correct earthing and compliance with the manufacturer's installation instructions are essential.

 

A surge protection device spd should also be coordinated with the site's wider lightning protection arrangement, particularly where electrical circuits cross Lightning Protection Zones.

Use a clear selection checklist

Before selecting a surge protection device type 2, check:

• System voltage

• Earthing arrangement

• Installation location

• Uc

• Up

• In

• Imax

• Single-phase or three-phase configuration

• Upstream protection requirements

• Need for downstream Type 3 protection

For a surge protection device spd matched to the actual installation rather than a generic specification, review the electrical system, protection zones and required performance with a qualified electrical professional. Sensitive electronic equipment may also require additional downstream Type 3 protection.

Protecting your electrical system starts with the right SPD

The right SPD depends on the system it is protecting. Axis India offers Type 1, Type 1+2 and Type 2 surge protection solutions for different electrical applications. Review the system requirements, compare the ratings, and choose the protection that fits the installation.

Frequently asked questions

Where is a Type 2 SPD normally installed?

A surge protection device type 2 is commonly installed at a main or sub-distribution board to limit transient overvoltages on downstream circuits.

 

Is a Type 2 SPD suitable for every building?

No. Selection depends on lightning exposure, the building's protection system, installation arrangement and applicable risk assessment.

 

Which SPD is best for a distribution board?

A surge protection device Type 2 is commonly used at distribution boards to limit transient overvoltages and protect downstream circuits. The final selection depends on the electrical system, surge exposure and overall protection arrangement.

 

What is the difference between Uc and Up?

Uc is the maximum continuous operating voltage. Up is the voltage protection level during the specified surge test.

 

How should SPD ratings be compared?

Check Uc, Up, In and Imax against the electrical system and installation conditions. A surge protection device (SPD) should be selected as a complete protection solution, not by kA capacity alone.