A common question after a lightning storm, switching event, or unexpected voltage surge is: does an SPD need to be replaced after a surge?

The short answer is no—not automatically.

A surge protective device is designed to limit transient overvoltage and divert surge current. If the surge is within the capability of the SPD and the device has not reached its end-of-life condition, it may continue protecting the system after the event.

However, a severe surge, repeated electrical stress, temporary overvoltage, overheating, or long-term degradation can damage the protective components inside an SPD. In these cases, the protection module may disconnect internally and the SPD may need to be replaced.

따라서 올바른 질문은 단순히 다음과 같은 것이 아닙니다.

“Has the SPD experienced a surge?”

올바른 질문은 다음과 같습니다.

“What condition is the SPD in after the surge?”

This guide explains what happens to an SPD during a surge, how to recognize signs of damage, what a green or red status indicator really means, and when you should replace the protection module or the complete SPD.

주요 내용

• SPD는 not automatically need replacement after every surge.
• One severe surge can cause an SPD to reach end of life, while smaller events may not.
• Repeated electrical and thermal stress can gradually change the characteristics of MOV-based SPDs.
• A red or fault indication normally requires attention according to the manufacturer’s instructions.
• A normal or green status indicator does not tell you the exact remaining surge capacity of the SPD.
• Visible overheating, cracking, melting, or other physical damage is a strong reason to remove the SPD from service and investigate.
• A basic multimeter cannot fully verify whether an SPD still meets its original surge-protection performance.

Does an SPD Need to Be Replaced After a Surge?

Whether an SPD should be replaced depends on its condition after the event.

The important point is that a surge event alone is not an end-of-life indication.

The actual SPD condition and the manufacturer’s maintenance instructions should determine the next step.

What Happens to an SPD During a Surge?

To understand why an SPD does not necessarily need to be replaced after every surge, it helps to understand what the device actually does.

During Normal Operation

Many power SPDs are connected in parallel with the circuit they protect.

During normal operating voltage, the voltage-limiting components inside the SPD remain in a high-impedance state. The normal load current therefore does not need to flow through the SPD protection element.

This is also why SPDs are normally installed in parallel rather than simply being placed in series with the load.

When a Surge Occurs

When a transient overvoltage reaches the SPD, its protective components respond.

In an MOV-based SPD, the metal oxide varistor changes from a high-impedance state toward a conductive state as voltage rises above its operating region.

The SPD then helps:

limit the transient voltage

및

divert surge current away from sensitive equipment.

When the transient event ends, the protection element normally returns toward its high-impedance state.

This operating principle is fundamental to surge protective devices: they contain nonlinear components designed to limit surge voltage and divert surge current. Current IEC requirements use the same basic definition.

Therefore, the fact that an SPD has operated during a surge does not by itself mean that it has failed.

Does One Surge Damage an SPD?

꼭 그렇지는 않습니다.

The result depends on factors such as:

• surge magnitude
• surge waveform
• duration
• number of surge events
• SPD design
• discharge-current capability
• 시스템 전압
• temporary overvoltage conditions
• temperature
• previous electrical stress

A surge that remains within the capability of the SPD may be handled without causing the device to reach end of life.

A much more severe event may cause significant damage in a single occurrence.

Small or Moderate Surge Events

An SPD is designed to respond to transient overvoltages.

If an event remains within the intended operating and surge-handling capability of the product, the SPD may continue working afterward.

This is why it would be incorrect to apply a rule such as:

“One surge = one replacement.”

The device must be assessed according to its actual condition.

Severe Surge Events

A sufficiently severe event can cause the protection element to reach its end-of-life condition in a single occurrence.

Depending on the SPD design, this may result in:

• activation of an internal thermal disconnector
• a red or fault status indication
• operation of a remote signaling contact
• visible heat damage
• disconnection of the protection module
• operation of an external backup protective device

The exact failure behavior varies by product design.

Repeated Surge Events

SPD degradation is also not limited to one dramatic lightning event.

Repeated electrical stresses can gradually affect an MOV’s electrical characteristics.

However, this should not be described as a simple fixed-energy countdown where every surge removes an identical amount of remaining life.

MOV degradation depends on the magnitude, duration, repetition, operating voltage, temperature, and other stresses applied to the component. IEC TR 61643-333:2026 specifically addresses characteristic equations and life evaluation for zinc-oxide MOVs, illustrating that MOV life is more complex than a simple fixed “joule balance.”

Why Can an SPD Wear Out Over Time?

Many Type 2 SPDs use metal oxide varistors as their primary voltage-limiting elements.

Under normal voltage, an MOV has high resistance.

When the applied voltage rises sharply during a transient event, the MOV becomes conductive and helps limit the voltage.

Over time, electrical and thermal stress can change the MOV’s characteristics.

A simplified aging path may look like this:

Repeated electrical stress

↓

Change in MOV characteristics

↓

Possible increase in leakage current

↓

Additional heating

↓

Thermal protection operates if necessary

↓

Protection element disconnects

↓

SPD indicates an end-of-life or fault condition

The precise sequence depends on the SPD design.

Modern MOV-based SPDs commonly include thermal protection because an MOV that becomes unstable or overheated must be safely disconnected from the power system.

For example, Schneider Electric describes some of its SPDs as using thermally protected MOVs and instructs replacement of the module when the corresponding indication shows loss of protection.

This internal disconnection is one reason a failed SPD can sometimes leave the protected equipment powered while surge protection for that mode is no longer available.

7 Signs Your SPD Should Be Replaced

There is no single inspection method that applies identically to every SPD.

If you are not sure whether an SPD has failed, see our guide on how to know if an SPD is bad.

However, the following signs usually justify replacement or further investigation.

1. The Status Indicator Shows Red or Fault

For many pluggable DIN-rail SPDs, the front status window provides the fastest visual indication of the protection module’s condition.

A common arrangement is:

Normal indication → protection element has not reported end of life

Red/fault indication → affected module requires replacement

예를 들어, ABB describes mechanical SPD indicators that change from green to red at end of life and states that once this occurs, the SPD should be changed because protection is no longer guaranteed.

However, indicator colors and meanings are product-specific.

Always check the markings, datasheet, or instructions for the exact SPD you are inspecting.

Do not assume that every SPD from every manufacturer uses the same color logic.

2. The Remote Signaling Contact Reports a Fault

Some SPDs include remote signaling terminals, often using a changeover dry contact with terminals such as:

COM

아니요

NC

These contacts allow the SPD’s status to be reported remotely to equipment such as:

• PLC 시스템
• alarms
• building-management systems
• monitoring systems
• SCADA 시스템

When the monitored SPD reaches the state defined by the manufacturer, the remote contact changes state.

But a remote alarm should still be verified.

Check:

1. the local SPD indicator
2. the manufacturer’s contact diagram
3. COM/NO/NC wiring
4. the monitoring circuit

The remote contact tells you about the monitored SPD state. It does not directly measure the SPD’s actual surge-clamping performance.

3. You See Burn Marks, Melting, or Serious Discoloration

Visible heat damage is not a normal service condition.

Warning signs include:

• blackened areas
• melted plastic
• severe discoloration
• damaged terminals
• signs of arcing
• heat-damaged conductors

If these conditions are present, the SPD should not simply be returned to service because its indicator still appears normal.

The circuit should be made safe according to the applicable electrical procedure, and both the SPD and surrounding installation should be inspected.

The cause also matters.

Replacing the SPD without identifying a wiring problem, abnormal system voltage, short-circuit condition, or other fault can result in another failure.

4. The SPD Housing Is Cracked or Deformed

A cracked housing may result from:

• mechanical damage
• excessive heat
• a severe electrical event
• environmental deterioration
• improper installation

Even if the internal condition cannot be seen, physical enclosure damage is a reason to treat the SPD as suspect.

An electrical protection device depends not only on its MOV or other internal component but also on proper insulation, spacing, mechanical connections, and safe containment.

If these have been compromised, replacement is normally the safer maintenance decision.

5. There Is a Burning Smell or Evidence of Overheating

Not every internal problem immediately produces an obvious red indicator.

If you notice:

• a burning smell
• abnormal heat
• softened plastic
• terminal overheating
• heat damage around the DIN rail or conductors

disconnect and investigate the equipment using the required safe electrical procedure.

Do not continue using an SPD simply because power is still reaching the protected equipment.

A parallel-connected SPD can lose its protective function while the main circuit continues supplying the load.

6. A Replaceable Protection Module Has Disconnected

Many modular SPDs use plug-in cartridges.

If an internal disconnector has operated and the cartridge indicates end of life, the affected cartridge normally needs replacement.

That does not necessarily mean the complete SPD base must always be replaced.

If:

• the base is undamaged
• the contacts are in good condition
• there are no signs of overheating
• the correct compatible replacement module is available

the manufacturer may allow replacement of the cartridge only.

Schneider Electric, for example, provides model-specific replacement modules for certain modular SPD families rather than requiring replacement of every part of the assembly.

But never assume that a pluggable SPD cartridge is automatically safe to remove while energized.

Pluggable does not mean hot-swappable.

Follow the manufacturer’s instructions and the required electrical isolation procedure before servicing the SPD.

7. The New SPD Keeps Failing Again

One of the most important warning signs is not the first failure.

It is repeated early failure after replacement.

If a newly installed SPD quickly reaches its fault or end-of-life condition again, simply installing another identical device may not solve the problem.

Investigate possible causes such as:

• incorrect Uc or MCOV selection
• system voltage higher than expected
• temporary overvoltage
• neutral or earthing-system problems
• wrong SPD configuration for the electrical system
• incorrect AC/DC application
• inadequate coordination
• installation errors
• severe or unusually frequent surge exposure
• unsuitable backup protection

For PV applications, correct voltage selection is especially important. See how to select the correct DC SPD voltage rating for a solar PV system.

Current IEC SPD requirements specifically consider system and fault conditions such as expected short-circuit current and temporary-overvoltage stresses when evaluating SPD applications.

Repeated failure should therefore be treated as a system-level troubleshooting problem, not merely a replacement problem.

Can an SPD Still Be Good If the Indicator Is Green?

Usually, a manufacturer-defined normal indication means the SPD has not reported its end-of-life condition through that indicator mechanism.

For a deeper explanation, see what an SPD green indicator can and cannot tell you about the protection condition.

But there is an important distinction:

Normal indicator ≠ exact measurement of remaining SPD life.

A basic mechanical indicator normally does not tell you:

• remaining surge-current capacity
• percentage of MOV life remaining
• exact degradation level
• future number of surges the SPD can withstand
• whether the original voltage-protection level has been independently verified

So avoid statements such as:

“Green means the SPD is 100% healthy.”

또는

“Green means the SPD has full surge capacity remaining.”

A more technically accurate interpretation is:

The SPD’s normal status indication shows that its internal monitoring or disconnection mechanism has not indicated end of life according to the product design.

That is useful information—but it is not the same as a complete electrical performance test.

ABB’s guidance illustrates this distinction well: the mechanical indicator is specifically an end-of-life indicator, changing state when the device reaches the defined replacement condition.

Should You Replace an SPD After a Major Lightning Event?

Not automatically—but the inspection should be more thorough.

The words “lightning event” can describe very different electrical stresses.

A distant lightning event that induces a relatively small transient is not the same as a severe nearby or direct lightning-current event.

The correct SPD type and coordinated protection system also matter.

For example, a Type 2 SPD is primarily tested for surge-current conditions different from those associated with the lightning-current testing of a Type 1 SPD.

So after a known major event, check more than just the color window.

Inspect:

• the SPD status indicator
• remote signaling status
• plug-in modules
• SPD base
• terminals
• conductors
• backup fuse or circuit breaker
• upstream and downstream protective devices
• evidence of damage elsewhere in the system

If nearby electrical equipment has also been damaged, or the lightning event was unusually severe, a more detailed electrical inspection is justified even when the status window has not changed.

For critical installations, follow the site’s maintenance plan, lightning-protection procedure, and manufacturer-specific recommendations.

Replace the SPD Cartridge or the Whole SPD?

For modular SPDs, a failed cartridge does not always require replacing the complete assembly.

Use the physical condition of the base and the manufacturer’s instructions to make the decision.

The most important rule is:

Replace only what the manufacturer allows you to replace.

A cartridge from a different series may physically look similar while having a different Uc, discharge rating, protection level, internal circuit, or coding system.

Always use the specified replacement module.

How to Check an SPD After a Surge

A practical post-surge inspection can follow seven basic steps.

Step 1: Check the Status Indicator

Start with the front status window.

Look for the manufacturer-defined normal, fault, or end-of-life condition.

Step 2: Check Remote Signaling

If the SPD includes remote contacts, verify whether the monitoring system has received a fault signal.

Compare the result with the manufacturer’s COM/NO/NC diagram.

Step 3: Look for Physical Damage

확인:

• burns
• cracking
• melting
• discoloration
• loose parts
• abnormal smell

Step 4: Inspect the Module and Base

For a modular SPD, inspect both the plug-in cartridge and the base.

A new cartridge should not be installed into a heat-damaged or mechanically damaged base.

Step 5: Inspect Connections

Loose or heat-damaged conductors can affect both safety and surge protection.

Also check the SPD connection conductors and protective-earth connection according to the installation instructions.

In solar PV systems, the distance between the SPD and inverter and the connection lead length can also affect practical surge protection performance.

Step 6: Understand the Event

Ask what happened before the SPD changed state.

Was there:

• a thunderstorm?
• a known lightning event?
• a supply fault?
• an abnormal system voltage?
• equipment switching?
• a neutral problem?
• repeated SPD failure?

This information can help distinguish normal end-of-life behavior from a broader installation problem.

Step 7: Replace or Test as Required

If the SPD has reached its defined end-of-life state or shows physical damage, replace the affected component according to the manufacturer’s instructions.

If the condition is uncertain and the application justifies deeper verification, use the appropriate professional SPD testing method or manufacturer-approved test equipment.

Can You Test an SPD After a Surge With a Multimeter?

A multimeter can be useful around an SPD, but it cannot fully prove that the SPD still has its original surge-protection performance.

For example, a multimeter may help with:

• checking a remote signaling contact
• confirming whether a dry contact is open or closed
• limited resistance or continuity checks where permitted
• troubleshooting associated wiring

But an ordinary multimeter does not reproduce the electrical conditions used to determine major SPD parameters such as:

• voltage protection level, Up
• nominal discharge current, In
• maximum discharge current, Imax
• impulse current, Iimp

If these ratings are unfamiliar, our DC SPD 사양 가이드를 참조하십시오. explains Ucpv, In, Imax, Up and other common SPD markings in more detail.

따라서

A successful multimeter continuity or resistance check is not proof that the SPD still meets its original surge-protection specification.

Professional SPD verification may require dedicated equipment capable of testing the relevant electrical characteristics.

Phoenix Contact, for example, provides dedicated CHECKMASTER equipment for electrical testing of compatible pluggable SPDs and notes that visual inspection alone may not reliably determine an SPD’s functional capability.

Also remember that some electrical tests performed elsewhere in an installation can interact with an SPD.

ABB installation guidance, for example, specifies that the SPD should be disconnected before certain insulation testing because the SPD can respond to the test voltage as though it were an overvoltage.

Always follow the SPD and test-equipment manufacturer’s instructions.

For a more complete inspection procedure, see our guide on how to test an SPD.

How Long Does an SPD Last?

There is no universal fixed service life that applies to every SPD.

It would therefore be misleading to say:

“Every SPD must be replaced after three years.”

or:

“An SPD always lasts ten years.”

Actual service life depends on many variables, including:

• electrical stress history
• surge magnitude and repetition
• 시스템 전압
• Uc or MCOV selection
• temporary overvoltage conditions
• SPD technology
• ambient temperature
• installation quality
• coordination with other SPDs
• lightning exposure
• manufacturer design

A severe event may cause end of life much earlier than expected.

Another SPD in a relatively quiet installation may remain serviceable for many years.

For that reason, condition-based inspection and manufacturer-defined status indications are generally more useful than assigning one universal expiration date.

SPD Replacement Decision Checklist

Use this quick decision guide after a surge event.

자주 묻는 질문

Does an SPD need to be replaced after every surge?

아니요.

SPDs are designed to respond to transient overvoltages. Experiencing a surge does not automatically mean the SPD has reached end of life.

Replace or service it when the manufacturer’s status indication, inspection results, electrical testing, or physical condition shows that it is no longer serviceable.

Can an SPD work more than once?

예.

Many SPDs are designed to withstand multiple surge events within their specified capability.

However, the number and severity of events an SPD can withstand cannot be reduced to one universal number because different surge stresses and product designs produce different effects.

Can one lightning strike destroy an SPD?

예.

A sufficiently severe lightning-related event can cause an SPD to reach end of life in one occurrence.

Whether this happens depends on the actual current and voltage stress reaching the SPD, the SPD type and ratings, installation, and the overall lightning and surge protection system.

Does a green SPD indicator mean the SPD is still good?

It normally means the SPD has not indicated its manufacturer-defined end-of-life state through that indicator.

It should not normally be interpreted as an exact measurement of remaining surge capacity.

Always check the product instructions for the specific meaning of its status window.

Should a red SPD be replaced?

For SPDs where red is defined as the end-of-life or replacement indication, yes—the affected module or device should be serviced or replaced according to the manufacturer’s instructions.

ABB, for example, states that when its standard SPD indicator changes from green to red at end of life, the SPD must be changed because protection is no longer guaranteed.

Can I replace only the SPD cartridge?

If the SPD uses manufacturer-approved replaceable modules and the base remains undamaged, replacing only the affected cartridge may be permitted.

Check that the replacement module has the correct model, voltage rating, and compatibility.

If the base, terminals, housing, or contacts have been damaged, replace the complete affected assembly as required.

Can I replace a pluggable SPD module while the circuit is energized?

Do not assume that you can.

A pluggable design makes maintenance easier, but it does not automatically mean the module is approved for energized replacement.

Follow the manufacturer’s instructions and the required electrical isolation and safety procedure before removing or installing an SPD module.

Can a multimeter tell if an SPD is still good?

Not completely.

A multimeter may help test remote contacts or perform limited circuit checks, but it cannot reproduce the surge test conditions needed to verify the SPD’s full protection performance.

Dedicated test equipment or manufacturer-defined electrical testing may be required for more detailed verification.

Final Decision: When Should You Replace an SPD?

Do not replace an SPD simply because a surge occurred.

An SPD is specifically designed to respond to transient overvoltage events, and one surge does not automatically mean the device has reached end of life.

Instead, base the decision on the actual condition of the SPD.

Replacement is normally justified when:

• the manufacturer-defined end-of-life indicator has operated
• the remote monitoring system reports a confirmed SPD fault
• an internal protection module has disconnected
• the housing or base is physically damaged
• there is evidence of overheating, burning, or melting
• manufacturer-approved testing shows the SPD is no longer serviceable

A normal status indication and the absence of physical damage generally mean there is no obvious end-of-life indication, but they do not provide an exact measurement of remaining surge capacity.

And if an SPD repeatedly fails shortly after replacement, do not simply install another one.

Investigate the system voltage, Uc or MCOV selection, temporary overvoltage conditions, electrical configuration, wiring, backup protection, and the severity of the surge environment.

The best replacement decision is therefore based not on:

“Did a surge happen?”

but on:

“What does the SPD condition tell us after the surge?”

About KUANGYA Surge Protective Devices

KUANGYA provides AC and DC surge protective devices for electrical distribution and solar PV applications, including modular designs with visual status indication and optional remote signaling functions for easier inspection and maintenance.

For photovoltaic DC applications, SPD selection should consider factors such as maximum PV system voltage, Ucpv, SPD type, discharge-current ratings, voltage protection level, system configuration, and installation position.

PV-side SPDs are specifically addressed by IEC 61643-31 for photovoltaic installations up to 1500 V DC.

If you need help selecting a replacement SPD, send us your:

AC or DC application + system voltage + required SPD type + quantity

and KUANGYA can help you check a suitable model.