La distanza dell'SPD dall'inverter è una parte importante della progettazione della protezione dalle sovratensioni fotovoltaiche, specialmente quando l'SPD è installato in un quadro di parallelo o vicino al campo fotovoltaico.

Hai installato un dispositivo di protezione contro le sovratensioni CC nel sistema fotovoltaico, ma l'SPD si trova all'interno del quadro di parallelo mentre l'inverter dista 20 o 30 metri.

Segue una domanda molto pratica:

Quell'SPD è ancora sufficiente per proteggere l'inverter?

Oppure dovrebbe essere installato un altro SPD più vicino all'inverter?

La risposta è:

Sì, la distanza è importante.

In un impianto fotovoltaico, la protezione contro le sovratensioni non è determinata solo dalla presenza di un SPD nel circuito in corrente continua. La distanza tra il campo fotovoltaico e l'inverter, la posizione dell'SPD, la lunghezza dei conduttori di collegamento dell'SPD, la tensione di tenuta a impulso dell'apparecchiatura e la disposizione della protezione contro i fulmini influenzano il concetto di protezione finale.

IEC 61643-32 affronta specificamente la selezione, l'installazione e il coordinamento degli SPD utilizzati in impianti fotovoltaici fino a 1.500 V DC. Distingue tra distanze brevi e lunghe tra i moduli fotovoltaici e l'inverter e fornisce requisiti specifici per il posizionamento dell'SPD.

Quindi la domanda corretta non è semplicemente:

“Ho già un SPD?”

È:

“L'SPD è installato nella posizione corretta per proteggere l'apparecchiatura che mi interessa?”

Risposta rapida

Per gli impianti fotovoltaici coperti dalle configurazioni pertinenti della norma IEC 61643-32:

• quando la distanza del percorso dei cavi tra i moduli fotovoltaici e l'inverter è inferiore a 10 m, un set di SPD può essere sufficiente, a condizione che siano soddisfatte le relative condizioni di protezione;
• quando tale distanza è pari o superiore a 10 m, la norma IEC 61643-32 stabilisce che sono necessari due set di SPD per proteggere adeguatamente sia i moduli fotovoltaici che l'inverter per le configurazioni trattate ai punti 6.2.1 e 6.2.2;
• laddove sia presente un sistema di protezione contro i fulmini esterno e non sia possibile mantenere la distanza di separazione richiesta, i requisiti di protezione sono più rigorosi e il secondo SPD presso l'inverter è obbligatorio nella configurazione trattata al punto 6.2.3.

Allo stesso tempo, non confondere questa distanza di sistema di 10 m con circa raccomandazione per il cavo di collegamento SPD di 0,5 m.

Descrivono due diversi problemi elettrici.

Punti di forza

Perché la distanza dell'SPD dall'inverter è importante?

Un malinteso comune è che il cavo in rame sia elettricamente insignificante durante una sovratensione.

Alla normale frequenza operativa o con corrente continua costante, tale ipotesi può sembrare ragionevole.

Una sovratensione causata da fulmini è diversa.

La corrente di sovratensione cambia estremamente rapidamente. Ogni conduttore possiede un'induttanza e, quando la corrente varia rapidamente attraverso tale induttanza, si sviluppa una tensione ai capi del conduttore.

La relazione fondamentale è:

ΔU = L × di/dt

Dove:

ΔU = caduta di tensione induttiva aggiuntiva attraverso il conduttore
L = induttanza del conduttore
di/dt = velocità di variazione della corrente di sovratensione

Questa equazione non è specifica per la protezione contro le sovratensioni. Si tratta di una relazione elettromagnetica fondamentale.

Per l'installazione di un SPD, tuttavia, spiega qualcosa di molto importante:

Il conduttore collegato all'SPD diventa parte del circuito di protezione contro le sovratensioni.

La guida all'installazione dei dispositivi di protezione contro le sovratensioni di Phoenix Contact fornisce un esempio illustrativo utilizzando un'induttanza del conduttore di circa 1 µH/m. Con una variazione di corrente di 10 kA in 10 µs, si può sviluppare una tensione di circa 1 kV su un metro di conduttore. Si tratta di un'illustrazione piuttosto che di un valore di progettazione universale, poiché l'induttanza effettiva dipende dalla geometria e dal percorso del conduttore.

Ecco perché i produttori di SPD sottolineano ripetutamente l'importanza di collegamenti brevi e diretti.

Up non è necessariamente la tensione vista dall'inverter

Supponiamo che la scheda tecnica di un SPD dichiari:

Livello di protezione di tensione Up = 2,5 kV

Un'interpretazione comune è:

“Se questo SPD interviene, l'inverter non vedrà più di 2,5 kV.”

È troppo semplicistico.

Su Up è il livello di protezione di tensione dell'SPD determinato in condizioni di prova specificate.

Una volta installato l'SPD all'interno di un impianto elettrico reale, deve essere considerata anche la tensione che si sviluppa lungo i conduttori di collegamento.

Un modo semplificato per considerare il livello di protezione installato è:

Tensione efficace presso l'apparecchiatura protetta ≈ Up dello scaricatore (SPD) + contributo di tensione dei conduttori di collegamento

Schneider Electric illustra questa relazione utilizzando l'equazione dell'induttanza dei conduttori e descrive il livello di protezione installato come l'Up dello scaricatore più la tensione sviluppata nei suoi collegamenti.

Ciò non significa che si debba semplicemente aggiungere un numero fisso a ogni scheda tecnica di uno scaricatore.

Il valore effettivo dipende da:

• lunghezza del conduttore,
• disposizione dei conduttori,
• area dell'anello,
• corrente di picco,
• forma d'onda del picco,
• schema di collegamento equipotenziale,
• e il punto in cui viene valutata la tensione.

La lezione pratica è molto più semplice:

Un buon SPD con un cablaggio scadente può fornire una protezione installata peggiore di quanto suggerito dalla sola scheda tecnica.

Se non si ha familiarità con Ucpv, In, Imax, Up e Iscpv, consulta la nostra guida su come leggere l'etichetta di un SPD in corrente continua prima di valutare il posizionamento dell'SPD.

La distanza tra SPD e inverter e la lunghezza dei cavi dell'SPD non sono la stessa cosa

Questa distinzione è fondamentale perché la distanza dell'SPD dall'inverter viene spesso confusa con la lunghezza dei conduttori di collegamento dell'SPD stesso.

Spesso si dice:

“L'SPD deve essere vicino.”

Ma “vicino” può riferirsi a due distanze completamente diverse.

Distanza 1: Campo fotovoltaico / Posizione dell'SPD rispetto all'inverter

Si consideri questa disposizione:

Campo fotovoltaico → Quadro di parallelo + SPD → 30 m di cavo CC → Inverter

La questione qui è se la protezione fornita a un'estremità del cavo lungo sia sufficiente per l'apparecchiatura all'altra estremità.

Si tratta di un problema di posizionamento e coordinamento dell'SPD a livello di sistema.

È qui che diventa rilevante la disposizione di 10 m della norma IEC 61643-32.

Distanza 2: Conduttori di collegamento propri dell'SPD

Now imagine:

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 la distanza dell'SPD dall'inverter 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 e 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 inferiore a 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.

Pertanto:

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 non say:

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

It says one set may be enough.

Perché?

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

e

Su = 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 come dimensionare un SPD CC per un impianto fotovoltaico.

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, la distanza dell'SPD dall'inverter 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:

Corde PV

↓

Scatola combinatore FV

• string fuses
• Isolatore DC
• SPD DC

↓

Long DC Cable

↓

Inverter

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.

Considerate:

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 non 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?

No.

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.

Ad esempio:

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 pari o superiore a 10 m, 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.

Pertanto:

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

Errori comuni

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”

No.

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”

No.

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”

No.

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.

Inverter

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

Installazione

• 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?

Sì.

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?

No.

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?

No.

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?

No.

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?”

È:

“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