Der Abstand des SPD zum Wechselrichter ist ein wichtiger Bestandteil der Auslegung des Überspannungsschutzes für Photovoltaikanlagen, insbesondere wenn das SPD in einem Generatoranschlusskasten oder in der Nähe des PV-Generators installiert ist.

Sie haben ein DC-Überspannungsschutzgerät in der PV-Anlage installiert, aber das SPD befindet sich im Generatoranschlusskasten, während der Wechselrichter 20 oder 30 Meter entfernt ist.

Daraus ergibt sich eine sehr praktische Frage:

Reicht dieses SPD noch aus, um den Wechselrichter zu schützen?

Oder sollte ein weiteres SPD näher am Wechselrichter installiert werden?

Die Antwort lautet:

Ja, der Abstand spielt eine Rolle.

In einer Photovoltaikanlage wird der Überspannungsschutz nicht allein dadurch bestimmt, ob irgendwo im Gleichstromkreis ein SPD vorhanden ist. Der Abstand zwischen dem PV-Generator und dem Wechselrichter, der Installationsort des SPD, die Länge der Anschlussleitungen des SPD, die Stoßspannungsfestigkeit der Betriebsmittel sowie das Blitzschutzkonzept beeinflussen das endgültige Schutzkonzept.

IEC 61643-32 befasst sich spezifisch mit der Auswahl, Installation und Koordination von SPDs in Photovoltaikanlagen bis 1.500 V DC. Es unterscheidet zwischen kurzen und langen Abständen zwischen den PV-Modulen und dem Wechselrichter und stellt spezifische Anforderungen an die Platzierung des SPD.

Die richtige Frage lautet also nicht einfach:

“Habe ich bereits ein SPD?”

Sie lautet:

“Ist das SPD am richtigen Ort installiert, um die Geräte zu schützen, die mir wichtig sind?”

Schnelle Antwort

Für PV-Anlagen, die unter die entsprechenden Konfigurationen der IEC 61643-32 fallen:

• wenn die Leitungslänge zwischen den PV-Modulen und dem Wechselrichter weniger als 10 m, kann ein Satz von SPDs ausreichen, sofern die geltenden Schutzbedingungen erfüllt sind;
• wenn dieser Abstand 10 m oder mehr beträgt, besagt die IEC 61643-32, dass zwei Sätze von SPDs erforderlich sind, um sowohl die PV-Module als auch den Wechselrichter für die in den Abschnitten 6.2.1 und 6.2.2 behandelten Konfigurationen ausreichend zu schützen;
• wenn ein äußeres Blitzschutzsystem vorhanden ist und der erforderliche Trennungsabstand nicht eingehalten werden kann, sind die Schutzanforderungen strenger und das zweite SPD am Wechselrichter ist in der in Abschnitt 6.2.3 behandelten Konfiguration zwingend erforderlich.

Verwechseln Sie dies gleichzeitig nicht mit diesem 10-m-Systemabstand mit der ungefähren Empfehlung für 0,5 m SPD-Anschlussleitungen.

Sie beschreiben zwei verschiedene elektrische Probleme.

Wichtigste Erkenntnisse

Warum ist der Abstand des SPD zum Wechselrichter wichtig?

Ein häufiges Missverständnis ist, dass Kupferkabel bei einem Überspannungsereignis elektrisch vernachlässigbar seien.

Bei normaler Betriebsfrequenz oder konstantem Gleichstrom mag diese Annahme plausibel erscheinen.

Ein blitzbedingter Stoßstrom ist jedoch anders.

Stoßströme ändern sich extrem schnell. Jeder Leiter besitzt eine Induktivität, und wenn sich der Strom schnell durch diese Induktivität ändert, baut sich über dem Leiter eine Spannung auf.

Der grundlegende Zusammenhang lautet:

ΔU = L × di/dt

Wo:

ΔU = zusätzliche induktive Spannung über dem Leiter
L = Leiterinduktivität
di/dt = Änderungsrate des Stoßstroms

Diese Gleichung ist nicht auf den Überspannungsschutz beschränkt. Es handelt sich um einen grundlegenden elektromagnetischen Zusammenhang.

Für die Installation von SPD-Geräten verdeutlicht sie jedoch etwas sehr Wichtiges:

Der an das SPD angeschlossene Leiter wird Teil des Überspannungsschutz-Stromkreises.

Die Installationsanleitung für Überspannungsschutz von Phoenix Contact liefert ein anschauliches Beispiel unter Verwendung von ca. 1 µH/m Leiterinduktivität. Bei einer Stromänderung von 10 kA über 10 µs können über einem Meter Leiter ca. 1 kV entstehen. Dies ist eher eine Veranschaulichung als ein universeller Auslegungswert, da die tatsächliche Induktivität von der Leitergeometrie und der Leitungsführung abhängt.

Deshalb betonen SPD-Hersteller immer wieder kurze, direkte Verbindungen.

Up ist nicht zwangsläufig die Spannung, die am Wechselrichter anliegt

Angenommen, ein Datenblatt für einen Überspannungsschutz (SPD) gibt Folgendes an:

Spannungsschutzpegel Up = 2,5 kV

Eine gängige Interpretation lautet:

“Wenn dieser SPD anspricht, wird der Wechselrichter nicht mehr als 2,5 kV sehen.”

Das ist zu einfach ausgedrückt.

Nach oben Der Spannungsschutzpegel des SPD wird unter festgelegten Prüfbedingungen bestimmt.

Sobald der SPD in einem realen elektrischen System installiert ist, muss auch die Spannung berücksichtigt werden, die über seinen Anschlussleitungen abfällt.

Eine vereinfachte Betrachtungsweise des installierten Schutzpegels ist:

Effektive Spannung am geschützten Gerät ≈ SPD Up + Spannungsbeitrag der Anschlussleitungen

Schneider Electric veranschaulicht diesen Zusammenhang mithilfe der Induktivitätsgleichung für Leiter und beschreibt das installierte Schutzniveau als SPD Up zuzüglich der in den Anschlüssen entstehenden Spannung.

Das bedeutet nicht, dass man einfach einen festen Wert zu jedem SPD-Datenblatt addieren sollte.

Der tatsächliche Wert hängt ab von:

• Leiterlänge,
• Leiteranordnung,
• Schleifenfläche,
• Stoßstrom,
• Stoßstromkurvenform,
• Potenzialausgleichsanordnung,
• sowie der Punkt, an dem die Spannung bewertet wird.

Die praktische Lehre ist viel einfacher:

Ein guter Überspannungsschutz (SPD) mit schlechter Verdrahtung kann einen schlechteren Schutz bieten, als es das Datenblatt vermuten lässt.

Wenn Sie nicht vertraut sind mit Ucpv, In, Imax, Up und Iscpv, lesen Sie unseren Leitfaden zu Wie man ein DC-SPD-Etikett liest vor der Bewertung der SPD-Platzierung.

Der Abstand zwischen SPD und Wechselrichter und die Leitungslänge des SPD sind nicht dasselbe.

Diese Unterscheidung ist entscheidend, da der Abstand des SPD zum Wechselrichter oft mit der Länge der eigenen Anschlussleitungen des SPD verwechselt wird.

Oft sagen Leute:

“Das SPD muss nah dran sein.”

Aber “nah” kann sich auf zwei völlig unterschiedliche Abstände beziehen.

Abstand 1: PV-Generator / SPD-Standort zum Wechselrichter

Betrachten Sie diese Anordnung:

PV-Generator → Generatoranschlusskasten + SPD → 30 m DC-Kabel → Wechselrichter

Die Frage ist hier, ob der an einem Ende des langen Kabels bereitgestellte Schutz für die Geräte am anderen Ende ausreicht.

Dies ist ein Problem der SPD-Platzierung und -Koordination auf Systemebene.

Hier wird die 10-m-Vorgabe der IEC 61643-32 relevant.

Abstand 2: Die eigenen Anschlussleitungen des SPD

Stellen Sie sich nun vor:

DC Cable → SPD → PE / Bonding Point

The SPD may be installed physically beside the inverter, but its connecting wires may be long and looped around the enclosure.

That is a different problem.

IEC 61643-32 states for the DC-side arrangement in Clause 9.2.5 that the total length of the relevant connecting cables, shown as L1 + L2, should be as short as possible and preferably should not exceed 0.5 m total lead length.

So:

10 m ≠ 0.5 m

The first concerns the distance between protected parts of the PV system.

The second concerns the SPD’s own electrical connection.

Mixing these two numbers produces a lot of incorrect SPD advice online.

What Exactly Does IEC 61643-32 Say About 10 m?

When engineers discuss der Abstand des SPD zum Wechselrichter in a PV system, the 10 m value is one of the most important distances to understand.

IEC 61643-32:2017 Clause 9.2.5 addresses installation of SPDs on the DC side.

For PV installations described in 6.2.1 und 6.2.2, it states that when distance E between the PV modules and inverter is equal to or greater than 10 m, two sets of SPDs are necessary to sufficiently protect both the PV modules and inverter.

When the distance between the protected units is weniger als 10 m, one set of SPDs may be enough. The standard also notes that, for common PV modules, the inverter normally has the lower rated impulse withstand voltage, so installation of the SPD close to the inverter is recommended.

This means that the often-mentioned “10-meter rule” is not simply an industry habit.

It has a specific basis in IEC 61643-32.

However, it should not be transformed into an oversimplified statement such as:

“Every solar installation anywhere in the world automatically requires two SPDs once the cable reaches exactly 10 meters.”

That is also incorrect.

IEC 61643-32 defines specific PV configurations, and national adoption, local installation standards, equipment instructions, risk assessment, and lightning protection conditions still have to be considered.

Which PV Installations Does the 10 m Requirement Apply To?

The context matters.

IEC 61643-32 separates common PV installations into several arrangements.

PV Installation Without an External Lightning Protection System

This is the configuration described in Clause 6.2.1.

In general, IEC illustrates protection at both the inverter side and PV-array side, but it allows one of the DC SPDs to be omitted under specified conditions.

For example, where the distance between inverter and PV array is less than 10 m and the voltage protection level of the remaining SPD is sufficiently coordinated with the PV array impulse withstand voltage, the additional SPD may not be necessary.

PV Installation With External LPS and Separation Distance Maintained

Clause 6.2.2 addresses a building with an external lightning protection system where the required separation distance between the LPS and PV installation is maintained.

Again, IEC generally shows protection at both ends but permits omission under specified conditions.

The DC-side 10 m principle in Clause 9.2.5 applies to this configuration as well.

PV Installation With External LPS and Separation Distance Not Maintained

This is a more severe condition.

When the required separation distance cannot be maintained, conductive PV components may become part of the lightning-current path.

IEC 61643-32 specifies Class I tested SPDs at the relevant locations for this configuration, and Clause 9.2.5 notes that the second SPD at the inverter is mandatory for the case described in 6.2.3.

If the difference between Class I, Class II and the commonly used Type 1, Type 2 and Type 1+2 terminology is unclear, see our guide to DC SPD classes and types.

Daher:

Do not use distance alone to decide the SPD Type when an external lightning protection system is involved.

The LPS design and separation distance must be evaluated first.

What Does “One Set of SPDs May Be Enough” Really Mean?

This sentence is important.

IEC does nicht say:

“If the PV cable is 9 meters long, one SPD is always enough.”

It says one set may be enough.

Warum?

Because distance is only one factor.

The SPD voltage protection level still has to be coordinated with the impulse withstand voltage of the equipment being protected.

IEC uses:

Uw = rated impulse withstand voltage of the equipment

und

Nach oben = voltage protection level of the SPD.

For effective equipment protection, IEC 61643-32 states that Up must be lower than Uw and generally recommends maintaining at least a 20% safety margin:

Up ≤ 0,8 × Uw

subject to the applicable exceptions and coordination conditions.

So a short cable does not excuse poor SPD selection.

The SPD still has to be electrically suitable for the equipment.

For a broader selection workflow covering voltage rating, Up, discharge-current ratings and installation conditions, see wie ein DC-Überspannungsschutz für eine Photovoltaikanlage zu dimensionieren ist.

A Simple PV Example

Consider two systems using exactly the same Type 2 DC SPD.

System A

PV Array → 5 m DC Cable → SPD → Inverter

The SPD is close to the inverter.

System B

PV Array → SPD → 30 m DC Cable → Inverter

Both systems contain one SPD.

But they should not automatically be treated as equivalent protection designs.

For the relevant IEC configurations, System B crosses the 10 m distance described in Clause 9.2.5, meaning protection at both ends must be considered according to the standard requirement.

The arrangement would typically become:

PV Array → SPD 1 → 30 m DC Cable → SPD 2 → Inverter

The exact SPD test class and ratings depend on the lightning protection condition and installation design.

The important point is:

One SPD located somewhere on a long PV cable does not automatically provide sufficient coordinated protection at both ends.

What If the SPD Is Inside the PV Combiner Box?

In this situation, der Abstand des SPD zum Wechselrichter becomes particularly important because the protection device may be located at one end of a long DC cable.

This is one of the most common real-world situations.

A commercial PV system may look like:

PV-Strings

↓

PV-Kombinator-Box

• string fuses
• DC-Trennschalter
• DC SPD

↓

Long DC Cable

↓

Wechselrichter

An installer opens the combiner box and sees a Type 2 SPD.

The natural question is:

“Why would I need another SPD? There is already one here.”

If the inverter is only a short distance away, the existing arrangement may satisfy the applicable protection requirements.

But if the cable route between the PV generator and inverter reaches the distance defined by IEC 61643-32, protection at both ends becomes relevant.

Phoenix Contact’s current PV application guidance follows the same basic arrangement: it identifies DC surge protection near the PV panels and DC protection near the inverter and specifically uses 10 m as the cable-distance criterion for the inverter-side location.

So the combiner-box SPD is not “wrong.”

It may simply represent only one protection location within a larger surge-protection concept.

What If the Inverter Already Has a Built-In SPD?

Now the situation becomes more interesting.

Suppose the system is:

PV Array → External SPD → 25 m DC Cable → Inverter with Built-In Type 2 SPD

Potentially, you already have protection at both ends.

But you cannot confirm that from the words:

“Built-in SPD”

alone.

You need to check what is actually inside the inverter.

Important questions include:

• Is the built-in SPD on the DC side?
• Does it protect every relevant DC input or MPPT arrangement?
• Is it Type 2 or Type 1+2?
• What is its Ucpv?
• What is its Up?
• Is it replaceable?
• Does the inverter manufacturer count it as part of the required system surge protection?
• Are additional external SPDs specified in the installation manual?

A built-in SPD may form part of the inverter-side protection stage.

But:

Built-in SPD does not automatically mean complete PV-system surge protection.

If this is the situation in your system, read My Solar Inverter Already Has an SPD — Do I Still Need an External SPD? for a detailed explanation of when built-in and external protection may need to work together.

This is why SPD location and inverter documentation must be considered together.

SPD Distance From Inverter Checker

Why Must SPD Connecting Wires Be So Short?

Now return to the second distance problem.

Even if your SPD is installed at exactly the correct system location, its wiring can still reduce protection performance.

Bedenken Sie:

Installation A

DC conductor → short connection → SPD → short PE connection

and:

Installation B

DC conductor → long loop → SPD → long loop → PE

The SPD model is identical.

Its datasheet Up is identical.

Its Imax is identical.

But the installed protection can be different.

Phoenix Contact explains that excessive SPD connection length raises the effective voltage protection level because of voltage developed across the conductor inductance. Its installation guidance references the 0.5 m connection-length principle and shows how conductor voltage has to be added to the SPD protection level when evaluating the complete installed protection.

IEC 61643-32 gives the same practical message for the DC side:

keep the SPD connecting cables as short as possible.

The 0.5 m figure should therefore be treated as a wiring target, not as a reason to mount an SPD exactly 500 mm from the inverter.

An Engineering Example of Lead-Inductance Voltage

Suppose we use a simplified conductor inductance of:

L ≈ 1 µH/m

and a surge-current rise of:

10 kA in 10 µs

Then:

di/dt = 1 kA/µs

For one meter:

ΔU = L × di/dt

ΔU ≈ 1 µH × 1 kA/µs

ΔU ≈ 1 kV

This is the type of example Phoenix Contact uses to demonstrate why lead length matters.

But this should nicht be turned into a calculator that claims:

“Every meter always adds exactly 1 kV.”

It does not.

Real values change with:

• conductor spacing,
• conductor shape,
• routing,
• loop geometry,
• current waveform,
• current magnitude,
• and the actual surge-current path.

The calculation is best used to explain the physics, not to produce false precision.

Can I Solve the Distance Problem by Using a Higher-kA SPD?

Nein.

Suppose one SPD has:

Imax = 40 kA

and another:

Imax = 80 kA

It is tempting to think:

“If my SPD is far from the inverter, I will simply install the 80 kA model.”

That does not solve the placement problem.

Imax describes the maximum discharge-current capability under the specified 8/20 µs test conditions.

It does not eliminate:

• long cable routes,
• conductor inductance,
• poor bonding,
• incorrect SPD location,
• excessive connecting-lead length,
• or lack of SPD coordination.

A higher Imax may be appropriate for some installations, but it is not a substitute for correct SPD placement.

Can a Lower Up Solve a Long-Distance Installation?

Again, not by itself.

A lower Up can improve equipment protection because it means the SPD limits voltage to a lower level under its specified test conditions.

But the final installed protection depends on the complete circuit.

Zum Beispiel:

SPD A

Up = 2.0 kV
Very long connecting conductors

SPD B

Up = 2.5 kV
Very short, direct connections

You cannot determine which installation produces the lower voltage at the equipment terminals from the SPD label alone.

The conductor voltage contribution also matters.

That is why SPD selection and SPD installation should never be treated as separate topics.

Does the Cable Route Matter, or Only the Cable Length?

The physical cable route matters too.

Cable length is an easy number to measure, but electromagnetic behavior is influenced by geometry.

For surge currents, good practice includes:

• keeping outgoing and return/current-path conductors close together where appropriate,
• minimizing loop area,
• avoiding unnecessary conductor loops,
• using short bonding paths,
• and following the SPD manufacturer’s recommended connection arrangement.

IEC 61643-32 itself emphasizes minimizing loop areas in DC-side installation diagrams and recommends direct earthing between SPD and inverter for optimum overvoltage protection.

So two systems with the same “10 m cable length” are not necessarily electromagnetically identical.

What Changes on the AC Side of the Inverter?

An inverter is connected to more than one electrical system.

It has a DC input from the PV array and an AC connection to the distribution system.

IEC 61643-32 also addresses the AC side of the PV installation.

For the AC side, it recommends that where the wiring between the SPD near the origin of the electrical installation and the inverter is 10 m oder mehr beträgt, the inverter should be protected by an additional SPD adjacent to the inverter.

For the more severe external-LPS configuration described in Clause 6.2.3, the additional SPD at the inverter is mandatory.

Phoenix Contact’s current selection guidance follows the same basic structure, showing an additional AC-side SPD near the inverter when the cable length to the main distribution is 10 m or more.

Daher:

A DC SPD does not replace AC surge protection.

Both electrical interfaces need to be assessed.

SPD placement is only one part of the overall protection architecture. For the relationship between SPDs, gPV fuses, DC isolators, combiner boxes and inverter protection, see our complete solar PV electrical protection guide.

Do Communication Cables Need Attention Too?

Modern PV inverters may also be connected to:

• RS-485,
• Ethernet,
• energy meters,
• data loggers,
• sensors,
• remote monitoring systems,
• weather stations,
• or control equipment.

These conductors can provide another path for transient overvoltages.

IEC 61643-32 states that when SPDs are required for the power circuits, surge protection should also be considered for telecommunications and signalling circuits associated with the PV system. Phoenix Contact makes the same practical recommendation for common inverter interfaces such as Ethernet and RS-485.

So an engineer reviewing inverter surge protection should ask:

“What conductors enter the inverter?”

not only:

“Where is the DC SPD?”

What If the Building Has an External Lightning Protection System?

This is where simplified internet advice becomes especially risky.

If a building has an external lightning protection system (LPS), first determine whether the required separation distance s between the lightning protection system and the PV installation is maintained.

Separation Distance Maintained

For the IEC configuration where the external LPS exists but separation distance is maintained, Class II tested PV SPDs are used at the relevant DC locations in the arrangement described by IEC 61643-32.

The 10 m DC-side placement principle still applies to the configuration covered by 6.2.2.

Separation Distance Not Maintained

If separation distance cannot be maintained, parts of the PV system can carry partial lightning current.

This changes the required protection concept.

IEC 61643-32 specifies Class I tested SPDs at the relevant locations for this configuration, and the protection arrangement becomes more stringent.

This is why you should never decide:

“Type 2 is enough because the cable is only 8 meters.”

without first knowing the lightning protection condition.

Distance is only one part of the design.

Practical Installation Scenarios

Scenario 1: Small Rooftop PV System

PV Array → 6 m DC Cable → Inverter

No external LPS.

A suitable SPD is installed close to the inverter.

In this case, one set of DC SPDs may be sufficient if the applicable IEC conditions, Up coordination, equipment withstand voltage, and manufacturer instructions are satisfied.

The fact that the distance is below 10 m helps, but it is not the only requirement.

Scenario 2: Combiner Box 25 m From the Inverter

PV Array → Combiner Box + SPD → 25 m DC Cable → Inverter

For the relevant IEC 61643-32 configurations, the distance is ≥10 m.

Protection should therefore be provided at both ends in accordance with the standard arrangement.

A second suitable SPD close to the inverter is required for the configurations addressed by Clause 9.2.5.

Scenario 3: Inverter Has Built-In Type 2 DC SPD

PV Array → External SPD → 25 m DC Cable → Built-In SPD → Inverter

This may already resemble a two-location protection concept.

But the built-in device must be checked against:

• IEC classification,
• Ucpv,
• Up,
• protected poles/modes,
• inverter topology,
• and manufacturer instructions.

Do not remove the external SPD simply because the inverter datasheet says “SPD included.”

Scenario 4: SPD Beside the Inverter but With Long Leads

PV Array → Inverter Cabinet

Inside the cabinet:

DC terminal → 80 cm wire → SPD → 70 cm PE wire

The system-level location may be good.

The SPD wiring is not.

The long connecting conductors can increase the installed protection level because of their inductive voltage.

In this case, the first fix is not necessarily another SPD.

It may be to redesign the connection.

Scenario 5: Building With External LPS and Separation Distance Not Maintained

Now cable distance alone is no longer the main issue.

The system has to account for partial lightning current, lightning equipotential bonding, SPD test class, and the complete LPS design.

This requires a lightning-protection-based SPD design rather than a simple “less than or greater than 10 m” decision.

Quick Engineering Decision Table

Häufige Fehler

Mistake 1: “One SPD Protects the Entire PV System”

An SPD protects according to its location, installation, and coordination with the rest of the system.

A device installed at one end of a long conductor should not automatically be assumed to provide the same protection at the other end.

Mistake 2: “10 m Is Just a Recommendation From SPD Manufacturers”

Nein.

The 10 m distinction appears directly in IEC 61643-32.

For the relevant DC-side configurations, ≥10 m leads to a two-SPD requirement for sufficient protection of both PV modules and inverter.

Mistake 3: “9.9 m Means One SPD Is Definitely Enough”

Also incorrect.

Below 10 m, IEC says one set may be sufficient.

Protection-level coordination and the rest of the installation still matter.

Mistake 4: “0.5 m Means the SPD Must Be Within 0.5 m of the Inverter”

Nein.

The 0.5 m guidance refers to the SPD’s relevant connecting conductors.

It is not the same measurement as the PV-array-to-inverter distance.

Mistake 5: “A Bigger kA Rating Fixes Poor Placement”

Nein.

Imax does not compensate for long conductors, poor bonding, or incorrect protection location.

Mistake 6: “A Built-In SPD Means External SPDs Are Unnecessary”

Not automatically.

Built-in protection has to be evaluated as part of the full PV protection concept.

Mistake 7: “If the DC Side Is Protected, the Inverter Is Protected”

The inverter also connects to AC and often to communication lines.

All possible surge-entry paths should be reviewed.

Field Checklist Before Deciding Whether You Need Another SPD

Before deciding that one SPD is enough, check:

PV Layout

• distance along the cable route between PV array and inverter;
• location of combiner boxes;
• location of existing SPDs;
• outdoor and indoor cable sections.

SPD

• IEC test class / SPD Type;
• Ucpv;
• Up;
• In;
• Imax or Iimp where applicable;
• Iscpv;
• protected modes;
• backup protection requirements.

Wechselrichter

• rated maximum DC voltage;
• rated impulse withstand voltage Uw, if available;
• built-in DC SPD;
• built-in AC SPD;
• manufacturer’s external SPD requirements.

Einrichtung

• SPD lead length;
• bonding conductor length;
• cable routing;
• loop area;
• PE routing;
• earthing arrangement.

Lightning Protection

• external LPS present or absent;
• required separation distance;
• whether separation distance is maintained;
• lightning equipotential bonding requirements.

Only after these points are understood should the designer decide whether an additional SPD is unnecessary, recommended, or required.

FAQ

Does the distance between the SPD and inverter really matter?

Ja.

The physical distance between protected parts of the PV system is specifically considered in IEC 61643-32, and long SPD connection leads can also increase the effective installed protection level.

These are two separate effects.

Do I need two DC SPDs when the PV array is 15 m from the inverter?

For PV installations covered by IEC 61643-32 Clauses 6.2.1 and 6.2.2, when the cable-route distance E between PV modules and inverter is equal to or greater than 10 m, Clause 9.2.5 requires two sets of SPDs to sufficiently protect both ends.

The exact SPD class and ratings still depend on the system and lightning protection arrangement.

If the distance is only 8 m, is one SPD definitely enough?

Nein.

IEC states that one set may be enough below 10 m.

The SPD voltage protection level, equipment impulse withstand voltage, installation arrangement, and other conditions still need to be satisfied.

Where should the single SPD be installed if the distance is less than 10 m?

IEC notes that common PV modules generally have a higher rated impulse withstand voltage than the inverter, and therefore recommends installing the SPD close to the inverter when one set is used.

Is 10 m measured as straight-line distance?

For practical application, the relevant distance is the electrical cable-route distance between the units, not simply the straight-line distance measured through the air.

Is 0.5 m the distance between the SPD and inverter?

Nein.

For the DC-side arrangement in IEC 61643-32 Clause 9.2.5, the 0.5 m recommendation refers to the total relevant SPD connecting leads, identified as L1 + L2 in the standard example.

Why does longer SPD wiring reduce protection?

Because the connecting conductors have inductance.

During a fast-rising surge current, the conductor develops an additional voltage:

ΔU = L × di/dt

This additional voltage contributes to the installed voltage appearing at the protected equipment.

Can an inverter’s built-in SPD count as the inverter-side SPD?

Potentially, yes.

But its Type/test class, Ucpv, Up, protected circuit arrangement, installation, and manufacturer requirements must first be verified.

Do not assume all built-in SPDs are equivalent.

Does a DC SPD protect the inverter from AC-side surges?

Nein.

DC and AC are separate surge paths.

The AC-side protection arrangement must be evaluated separately.

What if my building has an external lightning protection system?

First determine whether the required separation distance between the external LPS and PV installation is maintained.

If it is not maintained, IEC 61643-32 applies a more stringent lightning-current protection arrangement using Class I tested SPDs at the relevant locations.

Final Answer

Yes. SPD distance from inverter matters in solar PV surge protection design.

But there are two different distances that must not be confused.

The first is:

the cable-route distance between the PV array and inverter.

For the relevant IEC 61643-32 configurations:

E < 10 m

→ one set of SPDs may be sufficient if the required protection conditions are met.

E ≥ 10 m

→ two sets of SPDs are necessary to sufficiently protect both PV modules and inverter.

The second distance is:

the length of the SPD’s own connecting conductors.

These conductors should be kept as short as possible, with IEC 61643-32 giving a preferred total lead length of no more than approximately 0.5 m for the DC-side arrangement shown in Clause 9.2.5.

Neither rule should be used alone.

A technically sound PV surge-protection design also considers:

Up, Uw, Ucpv, SPD test class, lightning protection system, separation distance, bonding, earthing, cable routing, inverter built-in protection, AC-side protection, and SPD coordination.

The useful question is therefore not:

“How many SPDs does my solar system have?”

Sie lautet:

“Are the SPDs positioned, selected, and connected so that every vulnerable part of the system receives the required protection?”

That is the difference between simply installing an SPD and designing a coordinated surge-protection system.

Need Help Reviewing Your PV SPD Layout?

If you are unsure whether the existing SPD is far enough from the inverter to require another protection stage, send us:

• PV system voltage,
• inverter model,
• array-to-inverter cable distance,
• existing SPD location,
• SPD specifications,
• and a simple system layout.

KUANGYA can help you identify the SPD parameters and installation positions that should be checked before product selection.

You can also view our DC surge protective devices for solar PV systems for available Type 2 and Type 1+2 DC SPD options.

KUANGYA — Surge Protection for Solar PV Systems