How to Choose a DC SPD for Solar Installations in Spain

Solar photovoltaic systems are exposed to transient overvoltages caused by nearby lightning activity, switching operations, and disturbances transmitted through connected electrical circuits. These events may damage inverters, monitoring equipment, combiner boxes, and other sensitive components.

Choosing the correct DC SPD for solar installations in Spain requires more than matching a device to the nominal system voltage. Designers and installers must also consider the maximum PV open-circuit voltage, SPD classification, discharge capability, voltage protection level, system earthing arrangement, cable distance, installation location, and applicable standards.

However, choosing a DC SPD involves more than matching a device to a nominal system voltage. Designers and installers must also consider the maximum PV open-circuit voltage, SPD classification, discharge capability, voltage protection level, system earthing arrangement, cable distance, installation location, and applicable standards.

This guide explains how to choose a DC SPD for solar installations in Spain and identifies the technical information that should be confirmed before requesting a quotation.

Why Solar PV Systems Need DC Surge Protection

PV modules and their connecting cables are normally installed over large, exposed areas. Long DC cable routes can act as paths through which lightning-induced and switching-related transient overvoltages reach the inverter.

A surge does not necessarily have to originate from a direct lightning strike on the PV array. Nearby lightning can induce transient voltages in DC cables, while switching operations within the installation may also create electrical disturbances.

A DC SPD is designed to:

• Limit transient voltage to an acceptable level
• Divert surge current toward the protective earthing system
• Reduce electrical stress on inverter insulation
• Protect combiner-box and monitoring components
• Reduce the likelihood of downtime caused by surge-related damage

An SPD does not replace a fuse, circuit breaker, isolator, earthing system, or external lightning protection system. Each device performs a different protective function and must be coordinated as part of the complete PV design.

Regulations and Standards Relevant to Spain

Low-voltage electrical installations in Spain are governed by the Reglamento Electrotécnico para Baja Tensión, commonly known as the REBT. The applicable design must also consider the current technical instructions, project specifications, local requirements, and standards referenced by the regulation.

Spain’s official list of standards associated with the REBT includes:

• UNE-EN 61643-31 – Requirements and test methods for SPDs used in photovoltaic installations
• UNE-EN 61643-11 – Requirements and test methods for SPDs connected to low-voltage power systems
• UNE-HD 60364-4-443 – Protection against transient overvoltages of atmospheric origin or caused by switching

For international PV applications, the following IEC documents are also important:

• IEC 61643-31 – Requirements and test methods for SPDs on the DC side of PV installations
• IEC 61643-32 – Selection and application principles for PV DC SPDs
• IEC 60364-7-712 – Electrical installation requirements for photovoltaic power supply systems

IEC 61643-31 applies to SPDs connected to the DC side of PV installations with rated voltages up to 1,500 V DC.

Project requirements may differ according to the type of installation, risk assessment, location, inverter design, external lightning protection system, and requirements of the Spanish authorities or authorised installer. Product selection should therefore be confirmed by the project designer or qualified electrical professional.

Step 1: Calculate the Maximum PV Voltage

The first selection parameter is the SPD’s maximum continuous operating voltage for the PV system, normally identified as Ucpv.

Do not select an SPD only according to the inverter’s nominal operating voltage.

The maximum voltage of a PV string depends on:

• Number of modules connected in series
• Module open-circuit voltage, or Voc
• Lowest expected site temperature
• 모듈 온도 계수
• Design safety factors required by the project

PV module voltage increases as temperature falls. Therefore, the maximum cold-condition open-circuit voltage of the complete string can be higher than its value under standard test conditions.

The SPD’s Ucpv must be suitable for the maximum voltage that can appear continuously across the PV array.

Typical voltage classes

These are application examples, not automatic selection rules. The final SPD voltage must be based on the calculated maximum PV voltage and the manufacturer’s connection diagram.

Selecting an SPD with an insufficient Ucpv may cause premature operation, overheating, or disconnection. Selecting a voltage rating unnecessarily higher than required may result in a higher voltage protection level and less effective protection for sensitive equipment.

Step 2: Choose Type 1, Type 2, or Type 1+2

PV SPDs are normally classified according to the surge current they are designed to handle.

유형 2 DC SPD

A Type 2 SPD is commonly used to protect against induced lightning surges and switching overvoltages.

일반적인 애플리케이션은 다음과 같습니다:

• Residential rooftop PV systems
• Commercial rooftop arrays
• DC combiner boxes
• Array distribution boxes
• DC inputs of inverters
• Systems where direct lightning current is not expected at the SPD location

Type 2 devices are normally specified using nominal discharge current In and maximum discharge current Imax, based on an 8/20 μs current waveform.

유형 1 DC SPD

A Type 1 SPD is designed to discharge partial lightning current. It may be required where the lightning protection design indicates that lightning current can enter the electrical installation.

Type 1 selection is typically associated with:

• Buildings equipped with an external lightning protection system
• Installations where the required separation distance cannot be maintained
• Exposed utility-scale PV systems
• Locations identified by the lightning risk assessment
• Points where partial direct lightning current may enter DC circuits

Type 1 capability is normally expressed using impulse discharge current Iimp, based on a 10/350 μs waveform.

유형 1+2 DC SPD

A Type 1+2 SPD combines lightning-current and induced-surge protection in one device.

It may be considered for:

• Exposed PV sites
• Inverter inputs requiring combined protection
• Installations with external lightning protection
• Projects that specify both Type 1 and Type 2 performance at the same location

The SPD type must be selected according to the project’s lightning protection concept. It should not be chosen only because a higher type number appears more powerful.

Step 3: Compare In, Imax, Iimp, and Up

Different SPD ratings describe different aspects of performance.

Nominal discharge current: In

In indicates the current that a Type 2 SPD can discharge repeatedly under the specified test conditions, normally using an 8/20 μs waveform.

It is one of the principal ratings used when comparing Type 2 SPDs.

Maximum discharge current: Imax

Imax is the maximum 8/20 μs discharge current that the SPD can handle under its specified test conditions.

A high Imax rating alone does not prove that an SPD is suitable for a particular installation. It must be considered together with In, Up, Ucpv, short-circuit behaviour, connection arrangement, and the applicable test standard.

Impulse discharge current: Iimp

Iimp is used for Type 1 and Type 1+2 devices and represents lightning impulse current capability using a 10/350 μs waveform.

When Type 1 protection is required, compare the Iimp value per pole or protection mode according to the project specification.

Voltage protection level: Up

Up indicates the residual voltage that appears across the SPD during the specified discharge test.

The Up value should be lower than the impulse withstand level of the equipment being protected. Connection cables also add voltage during a surge, so the effective protection level at the inverter can be higher than the SPD’s catalogue value.

This is why short, direct SPD connections are essential.

Step 4: Confirm the PV System Configuration

A PV DC circuit may be floating, functionally earthed, or configured according to a specific inverter topology. The SPD must use a connection arrangement suitable for that system.

Before selecting the number of poles or protection modes, confirm:

• Positive conductor configuration
• Negative conductor configuration
• PE connection
• Whether either DC pole is earthed
• Inverter insulation and monitoring method
• Required SPD wiring topology
• Number of MPPT inputs
• Number of strings and combiner boxes

Do not assume that an AC SPD with a similar voltage can be used on the PV DC side. PV systems have specific continuous-voltage and fault-current characteristics. The device should be designed and tested for photovoltaic DC applications according to IEC/UNE-EN 61643-31.

Step 5: Check Short-Circuit and Backup Protection Requirements

A PV SPD must be able to disconnect safely if it reaches the end of its service life.

Important parameters include:

• PV short-circuit withstand capability
• Internal thermal disconnector
• Required upstream backup fuse
• Maximum permissible backup protection
• Available prospective fault current
• Coordination with gPV fuses or DC circuit breakers

The external backup fuse should not be selected only according to the SPD’s physical size. Follow the SPD manufacturer’s data sheet and verify compatibility with the PV string current and the system’s fault characteristics.

The SPD protects against transient overvoltage. The gPV fuse or DC breaker protects against overcurrent and short-circuit conditions. One device cannot replace the other.

Step 6: Select the Correct Installation Location

Typical DC SPD locations include:

• PV array or string box
• DC 컴바이너 박스
• Main DC distribution cabinet
• 인버터 DC 입력
• Both ends of a long DC cable route

The most suitable arrangement depends on cable length, exposure, lightning protection design, equipment withstand level, and project risk assessment.

For a compact rooftop installation with short DC cable routes, a Type 2 SPD near the inverter may provide the required protection when permitted by the design.

For longer routes between the PV array and inverter, coordinated SPDs may be required at both ends. This reduces the voltage stress that can develop along the cable and improves protection for equipment at each location.

Some industry design guidance uses approximately 10 metres as a point at which additional coordination should be considered. This should not be treated as a universal rule for every Spanish installation. The final placement must follow the applicable design standard, risk assessment, cable routing, and equipment manufacturer’s instructions.

Step 7: Keep SPD Connections Short

Even a correctly rated SPD can provide poor protection if it is installed with long or badly routed cables.

During a surge, cable inductance creates additional voltage. Longer conductors can therefore increase the total voltage reaching the inverter.

Good installation practice includes:

• Keeping conductors as short and direct as possible
• Avoiding unnecessary cable loops
• Routing positive, negative, and PE connections appropriately
• Using the conductor size specified by the manufacturer
• Providing a reliable PE connection
• Avoiding sharp bends where practical
• Separating protected and unprotected conductors
• Following the SPD wiring diagram exactly

The objective is to reduce the total connection length and minimise the effective protection level at the protected equipment.

Step 8: Consider the Enclosure and Environment

DIN-rail SPD modules do not automatically provide outdoor protection. Their environmental protection depends on the enclosure in which they are installed.

For rooftop and outdoor PV systems in Spain, check:

• Enclosure IP rating
• Ambient temperature range
• UV exposure
• Condensation risk
• 환기
• 고도
• Pollution level
• Terminal torque requirements
• Accessibility for inspection and replacement

The SPD’s declared ratings apply under the operating conditions stated in its data sheet. High internal cabinet temperatures should be considered, especially in outdoor enclosures exposed to direct sunlight.

Step 9: Plan Inspection and Replacement

SPDs are not permanent, maintenance-free components. Their protective elements can deteriorate after repeated surge events.

Useful maintenance features include:

• Visual status indicator
• Replaceable plug-in cartridge
• Remote signalling contact
• Clear model and voltage identification
• Accessible DIN-rail mounting

The module should be inspected according to the maintenance plan and after significant lightning activity or a known surge event.

Replace the module when:

• The status indicator shows end of life
• The thermal disconnector has operated
• There are signs of overheating or damage
• The device fails inspection or testing
• Replacement is required by the manufacturer’s instructions

Always isolate the relevant DC circuit and follow safe working procedures before inspection or replacement.

Practical Selection Table

This table is a preliminary guide only. It does not replace the project risk assessment or the work of an authorised electrical designer.

Information to Send When Requesting a DC SPD Quotation

Providing complete technical information helps the supplier select the correct product and prevents delays.

Send the following details:

1. Country and project location
2. Residential, commercial, industrial, or utility-scale application
3. Maximum calculated PV string voltage
4. Nominal DC system voltage
5. Required Type 1, Type 2, or Type 1+2
6. Required In, Imax, or Iimp
7. Required voltage protection level
8. Number of poles and connection diagram
9. 접지 방식
10. Inverter model and number of MPPT inputs
11. 설치 위치
12. Required quantity
13. Required certification and documentation
14. OEM label or packaging requirements
15. Delivery location and project schedule

If the SPD type is not yet confirmed, provide the PV module data, number of modules per string, minimum design temperature, inverter model, system drawing, and lightning protection information.

Common DC SPD Selection Mistakes

Avoid these common errors:

• Selecting the SPD only by nominal voltage
• Ignoring cold-condition PV string Voc
• Using an AC SPD on the DC side
• Choosing Type 2 where Type 1 capability is required
• Comparing products only by Imax
• Ignoring Up and equipment withstand voltage
• Installing the SPD with long connecting wires
• Using the wrong protection topology
• Ignoring backup-fuse requirements
• Installing indoor modules in an unsuitable outdoor enclosure
• Failing to inspect the status indicator
• Assuming one SPD automatically protects every part of a large PV installation

How to Choose a DC SPD for Solar Installations in Spain

Selecting a suitable DC SPD for solar installations in Spain requires coordination between the PV system voltage, lightning risk, SPD classification, installation location, earthing arrangement, and applicable Spanish requirements.

The most important steps are:

1. Calculate the maximum cold-condition PV voltage.
2. Select the correct Ucpv rating.
3. Determine whether Type 1, Type 2, or Type 1+2 is required.
4. Compare In, Imax, Iimp, and Up.
5. Confirm the system topology and number of protection modes.
6. Check short-circuit and backup-protection requirements.
7. Choose suitable installation locations.
8. Keep connecting conductors short.
9. Verify enclosure and environmental conditions.
10. Plan inspection and cartridge replacement.

KUANGYA supplies DC SPDs for solar PV applications in 600 V, 1,000 V, and 1,500 V configurations, including Type 2 and Type 1+2 options.

View the KUANGYA DC SPD range for photovoltaic systems or contact us with your system voltage, SPD type, discharge-current requirements, wiring configuration, quantity, and project location to request a data sheet and B2B quotation.

자주 묻는 질문

Is a Type 2 SPD suitable for every rooftop PV system?

Not automatically. Type 2 is widely used for induced lightning and switching surges, but the final selection depends on the lightning protection system, risk assessment, equipment location, and project requirements.

Can I use a 1,000 V SPD in a 1,000 V PV system?

Only if the SPD’s Ucpv is suitable for the maximum calculated PV voltage under the lowest expected temperature. Do not rely only on the nominal system description.

What is the difference between In and Imax?

In is the nominal discharge current used to evaluate repeated Type 2 surge performance. Imax is the maximum 8/20 μs discharge current the SPD can withstand under specified test conditions.

When is a Type 1+2 SPD used?

It is used where the design requires both partial lightning-current discharge and Type 2 surge-limiting performance at the same installation point.

Where should the DC SPD be installed?

Common locations include the combiner box and inverter DC input. Long cable routes or exposed systems may require coordinated SPDs at more than one location.

Which standard applies to photovoltaic DC SPDs in Spain?

UNE-EN 61643-31 is the principal Spanish standard covering requirements and test methods for SPDs used in photovoltaic installations. The complete installation must also follow the REBT and other applicable technical requirements.

Technical References

• Spain’s Low-Voltage Electrotechnical Regulation – REBT
• 2025 Spanish list of standards referenced by the REBT
• IEC 61643-31: Requirements for PV surge protective devices
• IEC 61643-32: Selection and application of PV DC SPDs
• IEC 60364-7-712: Requirements for PV installations

This article provides general technical guidance. Final SPD selection and installation should be verified by the responsible project designer or an authorised electrical professional in accordance with current Spanish requirements.