IEC 61643-31 Explained: The Standard Behind PV DC Surge Protection

In this guide

1. What IEC 61643-31 covers
2. Ucpv, In, Imax, Up, Iimp, Iscpv and overvoltage behaviour
3. IEC 61643-31 vs IEC 61643-11 and IEC 61643-32
4. Why PV SPDs need a specific test basis
5. How to screen a PV DC SPD: a worked example
6. How to verify the offered model and its documents
7. Common specification gaps
8. Frequently asked questions
9. Before you approve the order

CRESIN CSMS-B40 product example. Match the complete model, voltage variant and terminal arrangement to the documents supplied for your order.

1. What IEC 61643-31 Covers

The IEC catalogue lists IEC 61643-31:2018, including the June 2022 corrigendum. Its scope covers fixed PV-side SPDs for installations up to 1,500 V DC, including the DC interfaces of PV generators and inverters. Energy-storage applications such as batteries and capacitor banks are excluded from the stated scope. [1]

This distinction matters when a quotation says only “DC SPD.” Identify the actual circuit: PV string, combiner output, inverter DC input or battery connection. A device approved for one application should not be assumed suitable for another simply because both operate on DC.

For a hybrid PV-and-storage project, request an application review covering the relevant circuits and operating modes. Do not use a PV product declaration alone to justify a battery-bus application.

Also separate product evaluation from system design. The standard number on a datasheet is a starting point for reviewing the device. Selection of locations, protection types and coordination within the installation requires additional application information.

2. Key PV DC SPD Parameters Explained

Read every value together with its unit, protection mode and configuration. A figure for one plug-in module may differ from the rating of the complete assembly. The following explanations are practical reading aids; the applicable standard and model-specific documents remain the basis for technical acceptance.

2.1 Ucpv: Maximum Continuous Operating Voltage

Ucpv describes the continuous DC-voltage limit for a declared protection mode. It is different from the voltage protection level Up. Some product labels use the shorter notation Uc; ask the supplier to identify the PV rating and its connection arrangement.

Start with the maximum array open-circuit voltage established for the project, taking account of module data, the number of modules in series, site temperature conditions and applicable design rules. The voltage observed while the inverter is producing power is not a sufficient selection basis.

Then check how that voltage relates to the assembly's protected paths, such as positive-to-negative or a conductor-to-PE path. Do not multiply module ratings or assume a connection arrangement from the number of visible cartridges. Manufacturer data may distinguish a single module from a configured combination. [2]

A “1,500 V system” label does not automatically require Ucpv = 1,800 V. Confirm the project voltage and the manufacturer's application conditions. A higher SPD voltage rating cannot justify exceeding the voltage limits of the inverter, modules, cables or other equipment.

2.2 In: Nominal Discharge Current

In is a discharge-current rating associated with an 8/20 µs impulse waveform. It is relevant to the device's surge test performance, not its normal load-carrying current. [3]

For comparison, write down both the number and its label: for example, “In = 20 kA, 8/20 µs,” rather than “20 kA SPD.” Confirm which path or configuration the value covers. If test endurance matters to the purchase, request the applicable report sequence and acceptance results rather than treating a marketing number as a prediction of years in service.

2.3 Imax: Maximum Discharge Current

Imax is the manufacturer's declared maximum discharge-current rating for an 8/20 µs waveform. It is not interchangeable with In or Iimp. [3]

Suppose one offer states In = 20 kA and Imax = 40 kA, while another advertises only “40 kA.” Those offers cannot yet be compared on equal terms. Ask the second supplier to identify the parameter, waveform and configuration.

Do not turn Imax into a promise that the device survives exactly one real-world lightning event, or infer a maintenance interval from the ratio between Imax and In. Procurement should compare documented ratings and operating conditions, then establish an inspection and replacement plan.

2.4 Up: Voltage Protection Level

Up characterises the device's voltage-limiting performance under specified impulse conditions. It describes performance at the SPD terminals, rather than a guaranteed voltage at every connected item of equipment. [3]

Record the protection mode and test basis beside the Up value. A module rating, an assembly rating and a residual-voltage measurement at a selected current are not automatically equivalent. Ask the supplier to resolve any difference between the datasheet, label and report.

Equipment impulse withstand, connection layout and bonding also enter the protection review. Therefore, first establish that the SPD can operate at the required continuous voltage, then assess its protection level and installation. Choosing a higher Ucpv alone does not establish better protection. [4]

2.5 Iimp: Impulse Current for Type 1 Capability

Iimp is associated with Class I testing. Type 1 product documentation commonly identifies a 10/350 µs lightning-current waveform. That test duty differs from an 8/20 µs rating, so equal peak-current numbers do not establish equivalent performance. [4]

For a Type 1+2 PV SPD, request evidence for both claimed test classes and the associated ratings. A large Imax number alone does not demonstrate Type 1 capability. Whether the project needs Type 2 or Type 1+2 protection should follow its lightning-protection and surge-coordination design, rather than the buyer's preference for the largest number on a label.

2.6 Iscpv: Short-Circuit Current Rating

Iscpv relates to the prospective fault current for which the PV SPD is rated with its specified disconnector arrangement. It addresses a different condition from the impulse ratings In and Imax. [3]

Ask the designer for the available fault current at the proposed installation point. Ask the supplier for the corresponding Iscpv rating, disconnector details and any required external backup protection. Put these answers together in the selection record.

Do not assume that a high surge-current rating covers a high prospective short-circuit current. Likewise, “no backup fuse required” needs documented application conditions; it should not be treated as a universal property of all voltage variants or installations.

2.7 TOV, Thermal Stability and Failure Behaviour

A short impulse and a longer-lasting abnormal voltage impose different stresses. An impulse-current rating alone does not explain how the SPD behaves during sustained electrical overstress.

For PV devices, examine operating-duty performance, disconnector operation and failure-mode behaviour. These are identifiable topics in IEC 61643-31; they should not be replaced by a generic “TOV passed” statement. [3]

Thermal stability concerns cooling after stress while the device remains energised under specified conditions. Disconnection addresses a different function: removing a failing protective element from the circuit.

If a supplier claims temporary-overvoltage performance, request the test reference, AC or DC conditions, applied voltage, duration, tested connection and result. Do not transfer an AC neutral-displacement explanation directly to a PV DC circuit. Equally, do not assume that the absence of a TOV line in a short catalogue settles the device's safety performance.

Ask what happens when protection is lost: which part disconnects, how the status changes, whether a remote contact is provided and which replacement module is authorised. A status window and a remote contact communicate condition; neither replaces the required protection and disconnection functions.

3. IEC 61643-31 vs IEC 61643-11 and IEC 61643-32

These references answer different questions. Record the part number and edition explicitly rather than requesting an unspecified “IEC 61643 certificate.”

The IEC catalogue includes the June 2022 corrigendum in Part 31, the October 2026 corrigendum in Part 11:2025 and the June 2019 corrigendum in Part 32. Confirm the edition and applicable corrections required by the project. [1] [5] [6]

An AC-only report does not establish PV DC suitability. A product report also does not establish that the selected installation location, cabling or coordination is correct. Keep those reviews connected, while identifying who is responsible for each decision.

For the AC-side documentation, see our IEC 61643-11:2025 guide for SPD buyers.

4. Why PV SPDs Need a Specific Test Basis

A PV generator has a source characteristic that differs from a conventional AC supply. DC also lacks the periodic current zero-crossings present in AC. The product's protective components and disconnection arrangement must be assessed for the relevant source and fault conditions. [4]

When reviewing a report, separate three questions:

1. Surge performance: which claimed ratings and protection modes were evaluated?
2. Behaviour after electrical stress: what results support continued operation or the intended failure response?
3. Applicability to the delivered product: does the tested assembly match the quoted and supplied configuration?

A photograph of a test bench cannot answer those questions. Ask for identifiable records showing the test item, applicable reference, conditions and result. If only a summary is available initially, record what remains to be verified before approval.

A PV installation contains several electrical interfaces. Review the actual cable routes and SPD locations rather than selecting protection from the plant's power rating alone.

5. How to Screen a PV DC SPD: A Worked Example

Use a staged review so that an attractive price or headline current rating does not obscure an unsuitable configuration.

Step 1: Establish the project conditions

Collect the module datasheet, string arrangement, minimum design temperature, inverter model, earthing arrangement and proposed SPD location. Obtain the design team's maximum PV voltage and available fault-current assessment. Identify whether the protection design calls for Type 2 or Type 1+2 capability.

Step 2: Screen the declared operating voltage

Illustrative example: assume the project assessment establishes 1,080 V as the voltage against which the offered configuration must be screened for the relevant protection mode. This value is hypothetical and is not a universal design factor.

Step 3: Check protection and fault-current compatibility

For a candidate that passes the voltage check, review Up, the required test class, In, any declared Imax, Iimp where applicable, and Iscpv. Compare the exact assembly rather than a catalogue family name. Ask for the stated backup protection and connection instructions.

Step 4: Complete the installation review

Confirm SPD locations, lead routing, bonding, coordination with inverter protection and any additional protection needed along the circuit. Cable lengths and the existing lightning-protection arrangement can affect this review. Follow the project requirements and manufacturer instructions; the voltage table alone is not an installation design. [4]

Browse the CRESIN PV DC SPD range, then request a datasheet for the complete model proposed for your application.

String inverters at a PV installation. Confirm the actual DC-side and AC-side protection arrangement from the project design and equipment instructions.

6. How to Verify the Offered Model and Its Documents

Use the quotation, label, datasheet and supporting documents as one review package. A standards reference on the enclosure is not, by itself, evidence of third-party certification.

1. Identify the exact assembly. Record the full model code, voltage variant, base and cartridge combination, terminal arrangement and options such as remote signalling.
2. Identify the document type. Distinguish the manufacturer's declaration from a laboratory report and a certification body's certificate. Ask what claim each document supports.
3. Match the coverage. Check the model, configuration and ratings against the offer. If a document covers a family, request the evidence that includes the particular variant being purchased.
4. Check traceability. Record the issuing organisation, document number, date and standard edition. Verify a certification claim through the issuer's published verification route where available.
5. Resolve technical differences. Ask for a written explanation of mismatched voltage ratings, protection modes, current values, Up figures or disconnector requirements.
6. Compare the sample and delivery specification. Check markings, dimensions, terminals, accessories and replacement-module identification. Agree how a proposed substitution will be reviewed.

A useful purchasing record has one row per offered model, with a link or document reference for each important claim. Leave missing evidence visible. An empty field is more useful than an assumption that turns into a problem after delivery.

For the wider supplier assessment, use our SPD manufacturer qualification guide.

7. Common Specification Gaps

Send these questions with the request for quotation. Compare price and lead time after the technical differences are visible, rather than trying to reconstruct them once the order has been placed.

8. Frequently Asked Questions

Is IEC 61643-31 the same as IEC 61643-11?

No. Part 31 concerns PV DC SPD products; Part 11 concerns AC SPD products. Shared symbols do not make their application evidence interchangeable. Check the exact circuit and declared standard before comparing devices.

Does a PV installation need both DC and AC surge protection?

Both sides need to be considered in the system assessment. Identify the protection already included in the equipment and the additional measures required by the installation design. Do not assume one SPD at one interface addresses every exposed circuit. [6]

What Ucpv should a 1,500 V PV DC SPD have?

There is no universal answer based only on that label. Establish the maximum voltage for the relevant configuration and protection mode, then apply the manufacturer's limits and project requirements. Do not automatically substitute 1,800 V as a general rule.

Does a larger Imax mean a better SPD?

Not by itself. Compare the same parameter, waveform and configuration, then review voltage suitability, protection level, fault-current compatibility and supporting evidence. A single headline current cannot replace that assessment.

What does Type 1+2 PV mean?

It describes a PV SPD claiming both Type 1 and Type 2 capability. Request the associated test-class evidence and ratings. Do not infer both capabilities from Imax or from the product's appearance.

What should I check when a supplier claims TOV performance?

Ask for the applicable test reference, voltage, duration, circuit configuration and result. Also review the PV device's overstress, disconnection and failure-mode information. A short “TOV tested” statement leaves those application details unresolved.

Does an inverter's internal SPD eliminate external protection?

Its presence alone is not enough to decide. Check the inverter documentation, internal SPD capability, cable arrangement and the wider protection design. Record why any external SPD is included or omitted.

Can a PV DC SPD be used on a battery bus?

A Part 31 declaration alone does not establish that suitability. Request evidence for the battery circuit and its operating and fault conditions rather than extending a PV claim to another application.

How should I handle an older EN 50539-11 reference?

Ask which dated standard the project accepts and which reference appears on the actual product documents. Do not assume that a report to one reference automatically demonstrates compliance with another. Resolve acceptance with the specifying party before ordering.

9. Before You Approve the Order

A useful IEC 61643-31 review ends with an identified PV DC SPD configuration, a completed comparison of relevant ratings, traceable supporting documents and agreed application requirements. It should also tell the operator how to recognise lost protection and obtain the correct replacement.

Keep that record with the purchase order. It gives the supplier, installer and maintenance team a shared specification to work from when a model, voltage variant or accessory changes.

Request a PV DC SPD Selection Review

Send CRESIN your project information and request a proposed configuration with its available technical documentation:

• Module datasheet, modules per string and minimum design temperature, or the established maximum array voltage.
• Inverter model, earthing arrangement and single-line diagram.
• Proposed SPD locations, cable lengths and lightning-protection information.
• Available fault-current information and required SPD type, where already specified.
• Destination market, applicable standards, quantity and required options.

Ask for the complete model code, datasheet, connection instructions and the documents supporting its declared application and ratings.

Request PV SPD Selection

Technical References

1. IEC 61643-31:2018 — official scope and publication details.
2. IEC 61643-31 public preview — terminology and contents.
3. DEHN — lightning and surge protection for rooftop PV systems.
4. IEC 61643-11:2025 — official scope and publication details.
5. IEC 61643-32:2017 — selection and application principles.

This article explains product review and selection considerations. Exact test procedures, acceptance criteria and installation requirements should be taken from the applicable standards, project specification and model-specific instructions.