Schützt ein SPD vor Überspannung? Ja, aber die Antwort hängt davon ab, um welche Art von Überspannung es sich handelt. Ein Überspannungsschutzgerät ist in erster Linie dazu ausgelegt, transiente Überspannungen zu begrenzen, während temporäre Überspannungen (TOV) und dauerhafte anormale Spannungen eine andere Betrachtungsweise erfordern.

Der Begriff “Überspannungsschutz” kann irreführend sein, da nicht jede Überspannung ein transienter Stoß ist.

Betrachten Sie drei Situationen:

Ein blitzinduzierter Überspannungsimpuls erreicht eine Schalttafel nur für einen winzigen Bruchteil einer Sekunde.

Die Versorgungsspannung steigt aufgrund eines Netzfehlers für mehrere Sekunden signifikant an.

Oder ein loser Neutralleiter führt dazu, dass eine anormale Spannung an einem Teil der Anlage anliegt, bis der Fehler behoben ist.

Alle drei beinhalten Überspannung, aber es handelt sich nicht um dasselbe elektrische Ereignis.

Und ein SPD reagiert nicht auf alle in der gleichen Weise.

Der wichtigste Unterschied ist folgender:

Ein herkömmlicher SPD ist primär dazu ausgelegt, transiente Überspannungen zu begrenzen. Er sollte nicht automatisch als Schutz gegen temporäre oder anhaltende anormale Versorgungsspannung betrachtet werden.

Diese Unterscheidung beeinflusst die Auswahl des SPD, die Fehleranalyse und sogar die Art und Weise, wie Ingenieure ein beschädigtes SPD interpretieren.

IEC 61643-01:2024 definiert Niederspannungs-Überspannungsschutzgeräte (SPDs) als Geräte, die mindestens ein nichtlineares Bauelement enthalten und dazu bestimmt sind, Stoßspannungen zu begrenzen und Stoßströme abzuleiten. Für AC-Niederspannungsstromversorgungssysteme sind die Produktanforderungen festgelegt in IEC 61643-11:2025.

Kurzantwort: Schützt ein SPD vor Überspannung?

Ja – aber nur vor bestimmten Arten von Überspannung.

Ein SPD ist hauptsächlich ausgelegt für Transiente Überspannungen, wie sie durch Blitzeinwirkungen oder Schaltvorgänge verursacht werden.

Es ist normalerweise nicht dazu bestimmt, die Versorgungsspannung zu regeln oder Lasten zu trennen, solange die Effektivspannung zu hoch bleibt.

Die folgende Tabelle zeigt den grundlegenden Unterschied.

Deshalb ist die Frage:

“Verfügt meine Verteilung bereits über einen Überspannungsschutz (SPD)?”

nicht dasselbe wie:

“Ist meine Anlage gegen jede anormale Spannungsbedingung geschützt?”

Das ist sie nicht.

Transiente Überspannung vs. TOV vs. dauerhafte Überspannung

Das Wort Überspannung ist eine weit gefasste Kategorie.

Das Verständnis der Dauer und der Ursache des Ereignisses ist unerlässlich, bevor entschieden wird, welches Schutzgerät ansprechen soll.

1. Transiente Überspannung

Eine transiente Überspannung ist eine kurzzeitige Spannungsstörung.

Typische Ursachen sind:

• Blitzeinwirkungen;
• Schaltvorgänge;
• Schalten induktiver Lasten;
• Schalten von Kondensatoren;
• andere transiente Ereignisse im elektrischen System.

Die Standard-SPD-Prüfung verwendet üblicherweise Impuls-Wellenformen wie die 8/20 μs Stromwellenform assoziiert für Typ-2-Anwendungen.

Das Ereignis geschieht extrem schnell.

Dies ist genau die Umgebung, für die ein SPD ausgelegt ist. Wenn Sie den Begrenzungs- und Stromableitungsprozess genauer betrachten möchten, lesen Sie unseren Leitfaden zu wie ein DC-Überspannungsschutzgerät funktioniert.

2. Vorübergehende Überspannung — TOV

Eine TOV ist etwas anderes.

Die Spannung bleibt wesentlich länger erhöht als bei einem Impuls und ist im Allgemeinen eher mit dem Stromnetz als mit einer einzelnen Überspannung im Mikrosekundenbereich verbunden.

Mögliche Ursachen können sein:

• Erdschlüsse;
• Probleme mit dem Neutralleiter;
• Bedingungen der Systemerdung;
• Ferroresonanz;
• Probleme bei der Spannungsregelung;
• anormale Schaltzustände.

Die Stärke allein definiert das Risiko nicht.

Spannung + Dauer + Schutzart + Erdungssystem + SPD-Auslegung sind allesamt von Bedeutung.

ABB unterscheidet beispielsweise Uc, zwischen der maximalen Dauerspannung und UT, der temporären Überspannungsfestigkeit. Ihr OVR-Praxisleitfaden behandelt das TOV-Verhalten getrennt von der Stoßstromfestigkeit und zeigt, dass die auftretende Belastung von der Anschlussart des SPD und der Netzkonfiguration abhängt.

3. Anhaltende oder permanente Überspannung

Wenn eine anormale Versorgungsspannung andauert, anstatt sich wie ein temporäres Fehlerereignis zu verhalten, ändert sich die technische Problemstellung erneut.

Ein herkömmlicher parallel geschalteter SPD sollte nicht als Spannungsregler verwendet werden.

Ein Gerät zur Überwachung der Effektivspannung (RMS) und zur Einleitung einer Abschaltung ist normalerweise erforderlich, wenn das Konstruktionsziel wie folgt lautet:

Trennung der Last, wenn die Versorgungsspannung dauerhaft über oder unter einem akzeptablen Schwellenwert liegt.

Zum Beispiel Schneider Electric Harmony Spannungsüberwachungsrelais bieten Über- und Unterspannungsüberwachungsfunktionen. Dies ist eine andere Funktion als die Hochgeschwindigkeits-Überspannungsableitungsrolle eines SPD.

Warum kann ein SPD einen Stoßstrom bewältigen, wird aber durch eine TOV beschädigt?

This seems contradictory at first.

An SPD may discharge a very large surge current measured in kiloamperes.

This is why asking “does an SPD protect against overvoltage?” requires first identifying whether the event is a transient surge, a TOV, or a sustained abnormal supply condition.

So why could a much smaller abnormal AC voltage damage it?

Die Antwort lautet:

Energy is not determined by current magnitude alone. Time matters.

Consider an MOV-based SPD.

Under normal operating voltage, the MOV remains in a high-impedance state and conducts only a very small current.

When a transient surge raises the voltage sufficiently, the MOV becomes conductive.

Surge current is diverted through the SPD and the voltage is limited.

The surge then disappears very quickly.

The MOV returns toward its normal high-impedance state.

A simplified sequence looks like this:

That last condition is the problem.

If the voltage does not disappear quickly enough, the MOV may continue conducting.

Electrical energy then becomes heat.

In simplified form:

abnormal voltage → MOV current → power dissipation → temperature rise → disconnector operation or component damage

This is why:

40 kA Imax does not mean that an SPD can withstand any abnormal supply voltage.

Imax describes a defined surge-current capability.

TOV behavior describes a completely different type of electrical stress.

Uc, Up and TOV: Three Different Questions

Another common source of confusion is mixing voltage specifications together.

Suppose an SPD datasheet contains Uc, Nach oben and a TOV/UT specification.

They should not be compared as though they describe the same thing.

The IEC definition of an SPD focuses on limiting surge voltage and diverting surge current. IEC 61643-12:2020 separately covers selection, operation, location and coordination principles for AC power SPDs. If the differences between Uc, Up, In, Imax and Iscpv are not yet clear, see our Leitfaden für DC-SPD-Spezifikationen.

Does Higher Uc Mean Better TOV Protection?

Not automatically.

It is tempting to think:

Higher Uc = safer SPD.

Das ist zu einfach ausgedrückt.

A suitably higher Uc can give more operating-voltage margin, but SPD selection involves a tradeoff.

The device must remain stable at the expected continuous system voltage while still providing an appropriate surge protection level.

NIST researchers have described this design dilemma for decades: an SPD must provide effective surge limitation without being expected to clamp longer-duration power-frequency overvoltages indefinitely.

Daher:

Do not deliberately oversize Uc simply because you are worried about TOV.

Instead, check:

Real Case 1: A Documented TOV Above 150% Lasted About Four Seconds

This is where the distinction stops being theoretical.

A NIST-hosted paper by François Martzloff and Arshad Mansoor discusses actual power-system overvoltage scenarios.

One example cited from an EPRI report involved a power-system switching incident during restoration of power phase by phase.

The recorded condition produced an RMS voltage exceeding 150% of normal voltage for approximately four seconds.

The researchers identified the phenomenon as a temporary overvoltage associated with ferroresonance.

Notice what makes this different from a normal SPD surge event:

Four seconds may sound short to a person.

For an MOV that is dissipating abnormal power continuously, it is extremely long compared with a microsecond-scale surge.

Real Case 2: Commercial SPDs Were Tested Under Simulated TOV Conditions

Another NIST-hosted TOV study by researchers from Eaton Electrical, EPRI Solutions and François Martzloff investigated what happens when commercial SPDs experience several TOV conditions.

The study intentionally exposed commercial devices to conditions representing real power-system abnormalities.

The test program included the following examples:

The values relate to the study’s 120 V system basis; they must nicht be copied directly as ratings for another SPD or another electrical system.

The result was especially important.

The researchers found that SPD response varied substantially depending on the product design.

The three cord-connected SPD specimens failed under the simulated 1.5 pu neutral-loss condition, while the two permanently connected specimens used in that study survived the first four test scenarios. Under the extreme 3.0 pu test, the permanently connected specimens experienced partial internal failure but retained some protective capability.

This should nicht be interpreted as:

“Hardwired SPDs always survive TOV.”

The study used only a small group of specific products and represents historical designs.

Its real lesson is more useful:

Two products with similar-looking surge ratings may behave very differently under a long-duration abnormal voltage condition.

That is why TOV cannot be judged from Imax alone.

Does an SPD Protect Against Overvoltage Caused by Neutral Loss?

Neutral interruption is one of the most useful examples because it explains why the phrase “the SPD should clamp the voltage” can become dangerous.

In a multi-wire system with unequal phase-to-neutral loads, loss of the neutral can shift the neutral point.

The voltage across individual loads can then become severely unbalanced.

NIST describes loss-of-neutral conditions in North American 120/240 V three-wire systems where one side can approach twice normal voltage depending on the connected load impedances. The paper notes that such neutral problems may result from loose connections, mechanical damage or corrosion.

Now imagine an MOV-based SPD connected across the affected conductors.

If the abnormal power-frequency voltage pushes the MOV into conduction:

it begins conducting continuously.

But an MOV is not supposed to behave like a voltage regulator carrying that current indefinitely.

It may heat rapidly.

Eventually the result may be:

The last point is particularly important.

A typical parallel-connected SPD can disconnect itself while the protected circuit remains energized.

Daher:

SPD failure or disconnection does not necessarily remove the abnormal voltage from the load.

A conventional SPD should therefore not be relied on as the sole protection against neutral-loss overvoltage. Where the design requires abnormal RMS voltage to be detected and the load disconnected, a dedicated voltage-monitoring or protection function may be needed. The neutral fault itself must still be located and corrected.

Why Doesn’t the SPD Simply Clamp the TOV?

Because doing so could require the SPD to absorb or divert power continuously.

Consider a simplified example.

A Type 2 MOV-based SPD is installed across the supply.

A brief transient occurs.

The MOV conducts for a very short time and then stops.

That is normal.

Now assume abnormal mains voltage remains high for many seconds.

If the MOV attempts to hold the voltage down continuously, the SPD essentially becomes part of a power-frequency current path.

The longer the current flows, the greater the thermal stress.

That can lead to:

thermal runaway → disconnector operation → loss of SPD protection or component damage

This is exactly why SPDs require coordinated fault and disconnection behavior rather than simply “clamping everything.”

TOV Withstand Does Not Mean TOV Protection for the Load

This distinction is extremely important when reading datasheets.

Suppose a manufacturer states that an SPD has a certain UT or TOV capability.

That generally describes the SPD’s behavior under specified test conditions.

It does not automatically mean:

“The downstream equipment will remain at normal voltage throughout the TOV.”

These are different functions.

Compare them:

Schneider’s Harmony control relays, for example, monitor overvoltage and undervoltage conditions with threshold and timing functions; this is fundamentally different from the shunt surge-diversion function of an SPD.

Can a Circuit Breaker Protect Against Overvoltage?

A standard circuit breaker should not automatically be treated as an overvoltage protector either.

Its primary job is overcurrent protection.

If voltage rises while load current remains below the breaker trip characteristic, an ordinary breaker may remain closed.

That means four devices can perform four different functions:

This is why replacing one device with another based only on the word “protection” is a mistake. For the separate question of SPD overcurrent coordination, see our guide to SPD backup fuse and circuit-breaker selection.

Can a Bigger kA SPD Solve a TOV Problem?

Nein.

Suppose one SPD is rated:

In = 20 kA
Imax = 40 kA

and another says:

Imax = 60 kA

The 60 kA product is not automatically better at surviving a temporary power-frequency overvoltage.

The ratings describe different stresses.

Therefore, if SPDs repeatedly fail without obvious lightning activity, simply purchasing a higher-Imax model may not solve the actual problem.

Repeated SPD Failure: What Should You Investigate?

This is a situation where field diagnosis matters more than changing brands.

Use this investigation table.

NIST’s historical analysis lists power-system faults, poor voltage regulation, conductor problems, generator conditions, ferroresonance and loss of neutral among conditions capable of contributing to SPD overvoltage stress. If a device already shows a red indicator, abnormal heating or visible damage, our guide on wie man erkennt, ob ein SPD defekt ist explains the next inspection steps.

What About TOV in Solar PV DC Systems?

Extra care is required here.

Most discussion of power-frequency TOV relates to AC systems.

A PV DC system has different operating conditions.

Important PV DC concerns include:

IEC 61643-31:2018 specifically covers SPDs intended for the DC side of PV installations up to 1500 V DC. IEC 61643-41:2025 now covers general DC low-voltage SPDs up to 1500 V DC, but it explicitly excludes PV applications, which remain within IEC 61643-31.

Therefore, do not take an AC TOV number from a 230/400 V AC SPD datasheet and assume the same rule applies to a 1000 V or 1500 V PV SPD.

For PV systems, check the exact:

Ucpv + topology + protection mode + manufacturer documentation + applicable PV SPD standard.

For voltage selection, see our DC SPD voltage selection guide. For grounded versus floating PV arrangements and protection paths, see 2P vs 3P DC SPD for Solar PV.

AC SPD vs PV DC SPD Under Overvoltage

This is another reason AC and DC SPDs should not be interchanged casually.

IEC currently lists IEC 61643-11:2025 for AC low-voltage SPDs, while IEC 61643-31:2018 addresses PV DC SPDs. For a practical explanation of why an AC-only SPD should not simply be moved to a DC circuit, see What Happens If You Use an AC SPD on a DC System?.

Common Mistakes About SPD and Overvoltage

How to Select an SPD When TOV Is a Concern

Instead of starting with:

“How many kA do I need?”

start with the electrical system.

Installation also matters after the product is selected. Long SPD connecting conductors can increase the voltage appearing at the protected equipment during a fast surge; see our guide to SPD distance from the inverter and SPD lead length.

This order avoids a common purchasing mistake:

choosing the largest kA number first and checking voltage compatibility later.

Practical Example: Diagnosing an SPD That Keeps Failing

Assume an electrician installs a new Type 2 SPD.

A few days later the status window indicates replacement.

A new cartridge is installed.

It fails again.

It would be easy to conclude:

“The SPD quality is poor.”

But that is only one possibility.

A better troubleshooting sequence is:

Only after these checks should repeated SPD replacement be treated as a simple product issue.

SPD vs Overvoltage Relay: Do You Need Both?

In some installations, yes.

They solve different problems.

Think of them this way:

SPD:
“What happens if a very fast surge arrives?”

Voltage monitoring protection:
“What happens if the supply voltage remains abnormal?”

A system containing both functions may therefore provide broader protection than either one alone.

But the exact protection design depends on the installation, applicable codes and equipment requirements.

SPD Overvoltage Protection Checklist

Before approving an SPD specification, confirm the following:

Häufig gestellte Fragen

Does an SPD Protect Against Overvoltage or High Voltage?

An SPD primarily protects against transient overvoltage, such as short-duration surges caused by lightning effects or switching events. It should not automatically be treated as protection against every temporary or sustained abnormal supply voltage. If the supply voltage remains excessively high, separate voltage monitoring or disconnection protection may be required.

Can an SPD protect against temporary overvoltage?

It depends on the SPD and the specific TOV condition.

The datasheet or manufacturer documentation may specify TOV withstand or behavior for defined voltage, duration and connection conditions.

Do not assume that every SPD will survive every TOV.

What happens if mains voltage stays above the SPD’s Uc?

The result depends on how far the voltage exceeds Uc, how long it lasts and the SPD design.

In an MOV-based SPD, excessive continuous voltage can increase MOV current and heating.

This may eventually cause thermal disconnection or damage.

Is TOV the same as a lightning surge?

Nein.

A lightning-related surge is a short transient event.

A TOV lasts much longer and is usually associated with a power-system abnormality.

The stresses placed on an SPD are therefore very different.

Does Imax tell me the TOV capability?

Nein.

Imax is a surge-current parameter.

TOV behavior must be evaluated separately.

Does a 40 kA SPD protect against a 400 V overvoltage?

That question cannot be answered from 40 kA.

You need to know the nominal system voltage, Uc, connection mode, TOV declaration, duration of the abnormal voltage and the SPD design.

Can an SPD prevent damage from a broken neutral?

Do not rely on an SPD alone.

A broken or displaced neutral can create dangerous abnormal phase-to-neutral voltages.

Neutral integrity must be restored, and where required a dedicated voltage-monitoring and disconnection function should be used.

Can a circuit breaker replace an SPD?

Nein.

A conventional circuit breaker protects primarily against overcurrent and short circuit.

An SPD limits transient overvoltage.

They perform different functions.

Can an overvoltage relay replace an SPD?

Nein.

A voltage-monitoring relay can detect abnormal RMS voltage and initiate a switching action.

It does not replace the high-speed surge-diversion function of an SPD.

Schlussfolgerung

Also, does an SPD protect against overvoltage?

The technically correct answer is:

An SPD protects against transient overvoltage, but it should not be treated as universal protection against every temporary or sustained abnormal voltage condition.

Surge current ratings such as In, Imax and Iimp describe transient performance.

Uc/Ucpv describes continuous voltage compatibility.

Nach oben describes surge-voltage limitation.

And TOV behavior describes how the SPD responds to a specified temporary abnormal-voltage condition.

These parameters should never be treated as interchangeable.

Real-world research also shows why the distinction matters. NIST/EPRI investigations found dramatically different SPD responses to temporary-overvoltage conditions, ranging from survival to internal failure depending on the device and the applied stress.

The practical rule is simple:

First identify the electrical event. Then select the protection function.

Use an SPD for transient surge protection.

Use appropriate voltage monitoring or disconnection when persistent abnormal supply voltage must be detected and removed.

And if SPDs repeatedly fail, investigate system voltage, neutral condition, earthing, Uc/Ucpv and TOV conditions before simply replacing the module again.

For PV applications, always verify the exact SPD model against the system’s maximum DC voltage, PV topology and applicable IEC 61643-31 requirements.