SPDが故障しているかどうかを判断する方法について疑問をお持ちですか？ステータスインジケーターは通常、最初に確認すべき箇所ですが、それだけでサージ保護デバイスの状態のすべてを把握できるわけではありません。.

サージ保護デバイス（SPD）は、保護機能の一部が失われた後でも、外観上は完全に正常に見えることがあります。.

これにより、設置業者やシステム所有者にとって共通の課題が生じます。

SPDが故障しているかどうかをどのように判断すればよいのでしょうか？

最も迅速に確認できるのは、 ステータスインジケーターです。. 多くのモジュール式SPDにおいて、緑色の表示は監視対象の保護モジュールが正常な待機状態であることを示し、赤色または故障の表示は該当モジュールの点検または交換が必要であることを示します。.

ただし、インジケーターは診断の一部に過ぎません。.

SPDは、過熱、目視による損傷、リモートアラームの作動、バックアップ保護装置の動作、または異常に過酷な電気的イベントへの曝露によっても、点検が必要となる場合があります。.

そして重要な点として：

緑色のインジケーターは、サージ保護システム全体が完璧であることを証明するものではありません。.

SPDの状態を判断する正しい方法は、製品のインジケーター、目視点検、設置状況、イベント履歴、およびメーカーの指示を組み合わせて確認することです。.

SPDが故障しているかどうかを判断するにはどうすればよいですか？

ステータスインジケーターが故障状態を示している、1つ以上のモジュールが赤色になっている、筐体に焦げ跡や変形がある、ユニットが過熱している、リモートアラームが作動している、またはSPDが異常な電気的イベントを経験した場合、そのSPDは故障している可能性があります。インジケーターの意味については、必ずメーカーの指示書で確認してください。.

本ガイドでは以下について説明します。 SPDが故障している可能性を示す7つの実用的な兆候, 各兆候が実際に何を意味するのか、またモジュールやSPD全体をいつ交換すべきかについて。.

要点

• A 赤色または故障を示すステータス表示 は、SPDモジュールが本来の保護機能を提供できなくなっている可能性を示す最も明確な兆候の一つです。.
• A 緑色のインジケーターは、通常、モジュールの監視対象の状態のみを確認するものであり、, 残りのサージ耐量全体を保証するものではありません。.
• 焦げ跡、変形、異臭、または異常な発熱がある場合は調査が必要です。.
• 多くの電源用SPDは回路と並列に接続されているため、SPDが故障しても機器はそのまま動作し続けることがよくあります。 並列に （前項の続き）.
• 一般的なデジタルマルチメーター では、Up、In、Imax、Iimp、またはSPDの残寿命を確認することはできません。.
• 落雷のたびにすべてのカートリッジを自動的に交換しないでください。SPDを点検し、メーカーの事後対応手順に従ってください。.
• プラグイン式SPDの場合、ベースおよび周辺の設置環境に損傷がなく、かつメーカーが許可している場合に限り、ベースを交換せずに故障したカートリッジのみを交換できることがあります。.

SPDが「故障する」とはどういう意味か？

SPDは、過渡過電圧を制限し、サージ電流を敏感な電気機器から逸らして保護するように設計されています。.

現代の低圧用SPDには、通常1つ以上の非線形保護素子が組み込まれています。MOV（金属酸化物バリスタ）は、多くのタイプ2および複合型SPD設計で一般的に使用されています。.

IEC規格では、SPDを「サージ電圧を制限し、サージ電流を逸らすための少なくとも1つの非線形素子を含むデバイス」と定義しています。現在のIEC要件では、AC用、汎用DC用、および太陽光発電DC用の各アプリケーションが区別されています。.

通常のシステム電圧下では、サージ保護素子はほとんど導通しない状態を維持します。.

過渡過電圧が発生すると、SPDはサージ電流に対して低インピーダンスの経路を提供し、下流の機器に到達する電圧を制限する役割を果たします。.

しかし、このプロセスは電気的および熱的なストレスを生じさせます。.

繰り返されるサージイベント、深刻なサージ、異常なシステム電圧、またはその他の過酷な条件下では、保護素子が劣化する可能性があります。.

そのため、多くのMOVベースのモジュール式SPDには、以下が含まれています。 熱動遮断器.

保護コンポーネントが危険な状態に達した場合、遮断器はそれを回路から切り離すことができます。多くの製品では、この状態が機械的に赤/緑のステータスウィンドウと連動しています。.

例えば、フエニックス・コンタクトの資料では、サージ保護プラグが以下を組み合わせていると説明されています。 バリスタ、熱動遮断装置、およびローカルの緑/赤ステータスインジケーター.

例えば、フエニックス・コンタクトの資料では、熱動遮断装置とローカルの緑/赤表示を組み込んだプラグイン式バリスタモジュールについて説明されています。.

これにより、SPDはより安全に故障（フェイルセーフ）することができます。.

しかし、影響を受けた保護経路が遮断されると、システムは意図したレベルのサージ保護を維持できなくなる可能性があります。.

SPDが故障している可能性を示す7つの兆候

SPDのステータスインジケーターが赤色または故障を示している

通常、これが最初に確認すべき項目です。.

多くのプラグイン式SPDの前面には、小さな機械式ステータスウィンドウが備わっています。.

製品によっては、正常状態が以下のように表示される場合があります：

• 緑色
• 正常
• ノーマル
• 保護中

故障または交換が必要な状態は、以下のように表示される場合があります：

• 赤色
• 交換
• 故障
• 故障

多くのモジュール式MOVベース製品において：

緑色 → 監視対象の保護モジュールが有効であることを示します

赤色 → 内部で切り離しが発生しており、通常は該当モジュールの交換が必要です

ただし、これは すべてのSPDに共通する色のルールではありません.

メーカーによってインジケーターの仕様は異なります。一部のSPDでは機械式ウィンドウの代わりにLEDが使用されます。また、ディスプレイ、警報接点、シンボル、警報音、あるいはこれらの機能を組み合わせたものを使用する製品もあります。.

例えばシュナイダーエレクトリック社では、各相のサージ抑制機能が有効かどうかをLEDの状態によって示すSPDシリーズの仕様を定めています。.

したがって、正確なSPDモデルについては、常にマーキングと取扱説明書を確認してください。.

赤色表示は、電気システム全体が停止することを意味しますか？

通常はそうではありません。.

多くのパネル取り付け型SPDは、 並列に 電源回路と共に設置されます。.

そのため、電気負荷は通常、SPDを通過する電流に依存しません。.

SPD内部の断路器が作動した場合、その経路のサージ保護機能は失われますが、保護対象の機器は正常に動作し続ける可能性があります。.

これが、故障したSPDが見過ごされやすい理由です。.

照明は点灯したままです。.

インバータは動作を継続します。.

機械は運転を継続します。.

しかし、次の過渡現象は同じように制限されない可能性があります。.

2. 1つのモジュールが赤色で、他が緑色の場合

多極SPDは、1つのカートリッジだけを見て判断すべきではありません。.

例えば、マルチモジュール設置では以下のように表示されることがあります：

三相SPDに3つまたは4つのプラグインモジュールがある場合を想定する.

3つが緑色のままで1つがメーカーの故障状態に変化している場合、 SPD全体が完全に動作していると判断してはならない.

少なくとも1つの意図された保護経路が確保されていない状態です。.

Should you replace all modules when only one is red?

Not automatically.

Some modular SPDs are specifically designed so individual cartridges can be replaced.

If:

• only one cartridge has failed,
• the base is undamaged,
• the terminals show no overheating,
• the correct replacement cartridge is available,
• and the manufacturer allows individual replacement,

then replacing the affected cartridge may be sufficient.

However, if there is:

• severe overheating,
• arcing,
• damage to the base,
• several failed modules,
• melted plastic,
• repeated unexplained failures,
• or uncertainty about the condition of the assembly,

the complete SPD and surrounding installation should be investigated.

3. There Are Burn Marks, Discoloration, Cracks, or Deformation

The status indicator is not the only thing that matters.

Always inspect the physical condition of the SPD.

Warning signs include:

• Blackening
• Brown discoloration
• Melted plastic
• ハウジングのひび割れ
• Bulging or deformation
• Damaged terminals
• Loose cartridge
• 腐食
• 湿気による汚染
• アーク放電の兆候

An SPD showing obvious thermal or mechanical damage should not simply be left in service because its indicator still appears green.

Physical damage can be caused by several different conditions, including:

• severe surge stress,
• abnormal overvoltage,
• poor terminal connection,
• overheating,
• contamination,
• incorrect installation,
• inappropriate system voltage,
• or an electrical fault.

The cause therefore matters.

Simply changing the cartridge without understanding why it was damaged can allow the same problem to happen again.

A damaged SPD should be treated differently from a normally disconnected module

There is an important difference between:

A clean module that has reached its manufacturer-defined replacement condition

そして

An SPD showing burning, melting, arcing, or mechanical damage.

In the second situation, inspection should extend beyond the replaceable cartridge.

Check the:

• SPD base
• terminals
• conductor insulation
• backup protection
• earthing connection
• surrounding enclosure
• システム電圧
• connection condition

Severe physical damage is a reason to investigate the entire installation rather than simply installing a new plug.

4. The SPD Is Abnormally Hot or Produces an Unusual Smell

Electrical equipment naturally operates at different temperatures.

But an SPD that becomes unusually hot, produces a burnt smell, or shows progressive discoloration deserves immediate attention.

MOV-based protective components can experience increasing leakage and thermal stress as they degrade.

Proper SPD designs therefore use internal disconnecting or protective mechanisms to reduce the risk of an unsafe end-of-life condition.

What should you do if the SPD feels hot?

Do not diagnose an energized SPD by repeatedly touching it.

If abnormal heating is suspected, inspection should be carried out by qualified personnel using appropriate procedures and instruments.

考えられる原因は以下の通り：

• SPDの劣化
• sustained overvoltage
• incorrect Uc or Ucpv selection
• loose terminals
• excessive ambient temperature
• poor ventilation
• system faults
• unsuitable SPD application

A hot SPD does not automatically prove that the MOV itself has failed.

For example, a poorly tightened terminal can create local resistance and heating even if the surge component has not reached its end of life.

That is why the location of the heat and the overall installation condition should be investigated.

5. The SPD Remote Alarm Reports a Fault

Industrial SPDs frequently offer an optional remote signaling contact.

Instead of requiring someone to open the electrical cabinet and visually check the SPD, the remote contact can communicate the SPD’s model-defined condition to equipment such as:

• BMS（バッテリーマネジメントシステム）
• PLC
• SCADA
• monitoring panel
• alarm lamp
• maintenance system

Phoenix Contact, for example, offers SPD assemblies combining local green/red indication with remote signaling.

This is useful in:

• solar PV plants,
• telecom systems,
• industrial plants,
• data centers,
• energy storage installations,
• remote substations,
• unattended electrical cabinets.

What does a remote alarm prove?

Usually, it tells you that the SPD’s monitored mechanism has changed state.

It does not automatically tell you:

• how large the surge was,
• why the SPD failed,
• how much lifetime remains in other modules,
• whether the earthing system is correct,
• whether the installation leads are too long,
• or whether the SPD rating is correct.

Remote signaling is therefore a maintenance tool, not a complete SPD diagnostic system.

If a remote alarm appears, confirm the local SPD status and inspect the device according to the manufacturer’s instructions.

6. The SPD or Its Backup Protective Device Operates Unexpectedly

SPDs can be installed with upstream or dedicated overcurrent protection depending on the SPD design and system requirements.

If the associated fuse or circuit breaker operates unexpectedly, do not immediately assume that the breaker itself is faulty.

Possible causes can include:

• internal SPD damage,
• abnormal power-frequency overvoltage,
• short-circuit conditions,
• incorrect SPD selection,
• unsuitable backup protection,
• wiring problems,
• or other system faults.

The backup protective device and the internal SPD disconnector do different jobs.

The internal thermal disconnector may operate because a surge protection element has reached an unsafe thermal condition without necessarily creating the type of sustained overcurrent required to trip a conventional breaker.

So this situation is possible:

SPD = failed

Breaker = still ON

This does not automatically mean the breaker has failed.

Likewise, repeatedly fitting a larger breaker is not a correct solution to repeated SPD disconnection.

The cause of the SPD failure must be investigated first.

7. The SPD Has Experienced a Major Lightning or Surge Event

A major lightning or switching event is an important reason to inspect an SPD.

But it is important to use careful wording here.

A lightning event does not automatically mean the SPD must be replaced.

SPDs are specifically designed to handle transient surge currents within their declared performance capabilities.

Therefore:

Lightning nearby ≠ SPD automatically destroyed

However, after a known severe event, especially at a critical facility, it is good maintenance practice to inspect:

• visual indicator status,
• remote alarm status,
• physical condition,
• cartridges,
• terminals,
• protective conductors,
• backup protection,
• and manufacturer-required diagnostics.

If a module has entered the manufacturer’s failed state, replace it.

If there is visible damage, investigate further.

If everything remains normal, follow the manufacturer’s maintenance and post-event instructions rather than replacing the SPD without evidence.

Does a Green SPD Indicator Mean the SPD Is Definitely Good?

そうだ。.

This is one of the most important distinctions when inspecting an SPD.

If the manufacturer defines green as the normal state, a green indicator usually means something like:

The monitored disconnect mechanism has not indicated failure and the protection module remains in its normal available state.

That is useful information.

But it is not the same as proving every aspect of SPD performance.

A green indicator normally cannot prove:

• the SPD has its original remaining surge capacity,
• the voltage protection level Up is still exactly the declared value,
• the SPD is correctly sized for the system,
• Uc or Ucpv is correct,
• the earthing system is effective,
• all terminals are properly tightened,
• connection leads are sufficiently short,
• the required backup protection is correct,
• upstream and downstream SPDs are coordinated,
• every surge path is protected.

Think of the indicator as a condition signal, not a laboratory test.

If your SPD is still green, see our detailed guide to what an SPD green indicator can — and cannot — confirm about the protection system.

This is also why normal indication should be combined with periodic inspection.

Can an SPD Fail Without the Equipment Losing Power?

そうだ。.

This surprises many people.

A typical shunt-connected SPD is installed parallel to the circuit being protected.

A simplified arrangement looks like this:

Power Supply → Load

with the SPD connected from the live conductors toward the relevant protection path, such as PE.

The load does not normally receive its operating current through the SPD.

Therefore, when the SPD’s internal protective element is disconnected at end of life:

Load power may remain ON

while

surge protection may be reduced or lost.

This is exactly why local indicators and remote alarms are important.

Without inspection, a failed SPD can remain installed for months while everything downstream appears to operate normally.

Can You Test an SPD With a Multimeter?

When learning how to know if an SPD is bad, it is important to understand that a normal digital multimeter cannot fully verify surge protection performance.

This question needs a careful answer.

A normal multimeter cannot fully test SPD performance.

A digital multimeter cannot reproduce the standardized surge conditions used to determine major SPD ratings.

It cannot verify:

• In — Nominal Discharge Current
• Imax — Maximum Discharge Current
• Iimp — Impulse Discharge Current
• Up — Voltage Protection Level
• impulse durability
• complete remaining surge capacity

These characteristics require controlled test equipment and defined test procedures.

IEC SPD requirements use standardized testing to establish performance and safety characteristics; ordinary low-voltage resistance measurements are not substitutes for those tests.

What can a multimeter sometimes help check?

Depending on the SPD and the manufacturer’s instructions, a multimeter may help with:

• remote dry-contact continuity,
• basic wiring verification,
• investigation of an obvious short circuit,
• checking auxiliary circuits.

But there is no universal resistance reading that means “SPD good.”

For MOV-based products, the small test voltage produced by a normal multimeter may be far below the voltage at which the varistor significantly conducts.

A healthy MOV can therefore appear as very high resistance or open circuit.

A degraded MOV may also appear open under the same low test voltage.

So:

Open circuit on a multimeter does not prove the SPD is healthy.

Likewise:

A continuity beep is not a universal SPD pass/fail test.

Dedicated SPD or MOV test equipment can provide more useful diagnostic information for some products, but results must still be compared with manufacturer-defined values for that specific SPD.

Should You Use a Megohmmeter to Test an SPD?

Generally, do not apply an insulation resistance tester directly across an SPD unless the manufacturer specifically provides a procedure allowing it.

Megohmmeters use test voltages much higher than an ordinary multimeter.

Because an SPD is intentionally designed to conduct when voltage rises above certain conditions, insulation testing can:

• produce misleading readings,
• cause the SPD to conduct,
• interfere with the test,
• or potentially stress the device.

For system insulation testing, SPDs may need to be disconnected or removed according to the manufacturer’s instructions and applicable installation procedures.

Never assume an SPD should behave like ordinary insulation.

Why Do SPDs Fail?

Understanding the reason is important because simply installing another SPD may not solve the underlying problem.

1. Repeated Surge Exposure

Every surge does not necessarily destroy an SPD.

However, repeated surge activity can progressively stress protective components.

The actual service life depends on factors such as:

• surge magnitude,
• number of events,
• サージ波形,
• product design,
• system conditions,
• temperature,
• and protection coordination.

There is therefore no reliable rule such as:

“An SPD always lasts exactly five years.”

Calendar age alone does not determine SPD condition.

2. A Surge Exceeds the Device’s Capability

SPDs have declared surge-current capabilities.

A sufficiently severe electrical event can exceed the capability of a particular protection system.

This is one reason correct Type selection and coordinated surge protection are important.

Type 1, Type 2, and combined Type 1+2 SPDs are not simply different quality levels.

If you are unsure which classification applies, see our guide to Type 1 vs Type 2 vs Type 1+2 SPD for a more detailed comparison.

3. Temporary Overvoltage

A transient surge and a temporary overvoltage are not the same thing.

A surge is generally very short.

A temporary overvoltage, or TOV, can remain for much longer.

An SPD designed to conduct short transient energy should not be expected to clamp an abnormal power-frequency overvoltage indefinitely.

Improper TOV conditions can therefore create serious stress on an SPD.

Current IEC requirements specifically consider TOV and fault conditions as part of SPD application and testing.

4. Incorrect Uc or Ucpv Selection

Selecting an SPD with an unsuitable maximum continuous operating voltage can cause problems.

For AC systems, the relevant value is commonly expressed as ウク.

For photovoltaic applications, Ucpv is particularly important.

For photovoltaic DC applications, IEC 61643-31 specifies requirements and test methods for SPDs intended for the DC side of PV installations.

If you are not familiar with these ratings, our guide to DC SPD specifications explains Ucpv, In, Imax, Up and Iscpv separately.

If the SPD’s voltage rating is too low for the maximum voltage that can continuously appear in the system, the protection component can be stressed during normal or abnormal operating conditions.

For PV systems, remember that array voltage changes with temperature.

Maximum PV open-circuit voltage under expected low-temperature conditions therefore needs to be considered when selecting the DC SPD.

For the full selection process, see how to select the correct DC SPD voltage rating for a solar PV system.

5. Incorrect Installation

Even a good SPD can perform poorly if it is installed incorrectly.

Important installation factors include:

• wiring topology,
• polarity,
• grounding arrangement,
• 導体の長さ,
• conductor routing,
• terminal torque,
• backup protection,
• SPD location.

Long connection leads are particularly important because the inductive voltage developed along the conductors during a rapidly changing surge current can add to the voltage seen by the protected equipment.

SPD location and lead length are two different installation issues. See why SPD distance from the inverter matters for a detailed explanation of the 10 m system-distance rule and the approximately 0.5 m connection-lead recommendation.

This means SPD performance depends not only on the number printed next to 上へ, but also on how the SPD is actually installed.

6. Environmental Conditions

Environmental stress can also shorten SPD service life.

例を挙げよう：

• excessive cabinet temperature,
• moisture,
• condensation,
• dust,
• corrosive atmosphere,
• vibration,
• poor ventilation.

These conditions can affect terminals, insulation, contacts, and surrounding installation components even before the internal surge element reaches normal end of life.

How to Check an SPD: A Practical Inspection Process

A simple field inspection can follow this order.

Step 1: Identify the Exact SPD

Check:

• manufacturer,
• model,
• AC or DC application,
• Type classification,
• voltage rating,
• replacement cartridge number.

Do not install a cartridge just because it physically fits the base.

Step 2: Read the Status Indicator

Confirm what the indicator means for that exact product.

Do not automatically assume every green window means normal and every red window means failure without checking the manufacturer’s markings.

Step 3: Inspect Every Module

For multi-pole SPDs, inspect all cartridges.

One failed module can mean the complete intended protection arrangement is no longer available.

Step 4: Look for Physical Damage

をチェックする：

• burning,
• melting,
• discoloration,
• cracks,
• moisture,
• loose modules,
• damaged terminals.

Step 5: Check Remote Signaling

If remote signaling is installed, compare the remote alarm state with the local status.

A mismatch should be investigated.

Step 6: Consider Recent Events

Ask whether the installation recently experienced:

• lightning,
• switching events,
• abnormal system voltage,
• equipment faults,
• fuse operation,
• circuit breaker operation.

Step 7: Decide Whether to Replace or Investigate Further

Replace the SPD Cartridge or the Whole SPD?

Many DIN-rail SPDs are modular.

They consist of:

Base + replaceable protection cartridge

For reference, you can also view our DC surge protective device range, including modular Type 2 and Type 1+2 models with replaceable cartridges.

This allows easier maintenance.

Replace only the cartridge when:

• the product is designed for plug-in replacement,
• only the cartridge has reached its replacement condition,
• the base is undamaged,
• terminals are sound,
• there are no signs of overheating or arcing,
• and the correct compatible cartridge is available.

Consider replacing the complete SPD when:

• the base is burnt,
• terminals are damaged,
• plastic has melted,
• there has been severe arcing,
• multiple components are damaged,
• the SPD is non-modular,
• the original replacement cartridge is unavailable,
• or the manufacturer requires complete replacement.

Never bypass the SPD’s internal thermal disconnector or attempt to reset a sealed failed cartridge.

A cartridge that has entered its defined end-of-life condition is normally intended to be replaced rather than repaired.

Does a Failed SPD Need to Be Replaced Immediately?

If the manufacturer-defined indication shows that the intended surge protection path is no longer available, replacement should not be unnecessarily delayed.

The electrical system may continue running without it.

But that does not mean continued operation without surge protection is desirable.

This is especially important for:

• solar inverters,
• industrial control systems,
• PLCs,
• communication equipment,
• data centers,
• EV charging infrastructure,
• energy storage systems,
• expensive electronic loads.

The longer the failed SPD remains in place, the longer the equipment may remain exposed to the next transient event.

How Often Should an SPD Be Inspected?

There is no single inspection interval suitable for every installation.

Inspection frequency should consider:

• manufacturer instructions,
• site maintenance procedures,
• lightning exposure,
• system importance,
• environmental conditions,
• past surge activity,
• criticality of protected equipment.

Inspection is particularly useful:

• during routine electrical maintenance,
• after a known severe surge or lightning event,
• after unexplained protective-device operation,
• after changes to the electrical system,
• when a remote alarm occurs.

For unattended or critical installations, remote signaling can make it easier to detect a failed SPD quickly.

SPD Failure Does Not Always Mean the SPD Was Poor Quality

Seeing a failed SPD sometimes leads to the assumption:

“The SPD failed, so it must be defective.”

That conclusion is not always correct.

An SPD is a protective device exposed directly to electrical stress.

A failure indication may mean that it experienced the kind of abnormal condition its protective and disconnecting mechanisms were designed to handle safely.

The more useful question is:

Why did the SPD reach this condition?

Investigate:

• event severity,
• system voltage,
• Uc or Ucpv selection,
• SPD Type,
• installation,
• grounding,
• lead length,
• backup protection,
• TOV exposure,
• environmental conditions.

If the same SPD position fails repeatedly, replacing cartridges without investigating the system is not enough.

How to Know If an SPD Is Bad: Final Inspection Checklist

The easiest sign of SPD failure is a manufacturer-defined failure or replacement indication, commonly red on many modular SPDs.

But that should not be the only check.

An SPD should also be investigated if you find:

1. A red or failed status indicator
2. One failed module among several modules
3. Burning, cracking, melting, or discoloration
4. Abnormal heating or burnt odor
5. A remote fault alarm
6. Unexpected SPD or backup-protection operation
7. Evidence of a significant lightning, surge, or abnormal electrical event

At the same time, do not assume that a green indicator proves the entire surge protection system is perfect.

It usually confirms only the condition monitored by that particular SPD.

And do not rely on a normal multimeter resistance test to prove surge performance.

Correct SPD assessment combines:

product status + visual inspection + installation condition + event history + manufacturer instructions.

If a modular SPD has reached its defined end-of-life state, replace the affected cartridge or assembly as specified.

More importantly, if failure is repeated or accompanied by physical damage, investigate the underlying electrical system before simply installing another SPD.

Ultimately, how to know if an SPD is bad comes down to combining the status indication, physical inspection, event history, installation condition and manufacturer guidance rather than relying on a single test.

よくある質問

How to Know If an SPD Is Bad During a Basic Inspection?

Start with the manufacturer’s status indicator. If the product defines the displayed condition as normal and there is no physical damage or alarm, the monitored module remains in its normal indicated state. However, the status indicator does not prove complete surge performance or remaining lifetime.

Does green mean an SPD is good?

On many modular SPDs, green means that the monitored protection module has not entered its failure or disconnection state.

But always confirm the manufacturer’s markings because indicator systems vary between products.

Green should not be interpreted as proof that the complete installation is perfectly protected.

What does a red SPD indicator mean?

On many plug-in MOV-based SPDs, a red indicator means the protection module has reached a manufacturer-defined failed or replacement condition, often associated with an internal disconnector.

The affected cartridge normally needs to be replaced.

Check the exact product instructions before taking action.

Can an SPD still supply power when it has failed?

そうだ。.

Most panel-mounted SPDs are connected in parallel with the protected circuit.

The load can therefore remain energized even if the SPD protection element has been disconnected.

Can I test an SPD with a multimeter?

Only to a limited extent.

A multimeter may help check remote dry contacts or investigate certain basic electrical conditions when permitted by the manufacturer.

It cannot verify surge ratings such as Up, In, Imax, or Iimp, and there is no universal resistance value that proves an SPD is healthy.

Should I replace an SPD after every lightning strike?

Not automatically.

Inspect the SPD after a significant event and follow the manufacturer’s maintenance instructions.

Replace it if it shows a failure indication, physical damage, abnormal condition, or if the manufacturer specifically requires replacement after the event.

Can I replace only the red SPD cartridge?

Replaceable cartridges are common in modular SPDs. For example, Schneider Electric explains that when the SPD end-of-life indicator turns red, the cartridge should be replaced.

Often yes, if the SPD is designed with replaceable plug-in modules and the base is undamaged.

Use only the correct compatible replacement cartridge specified for that SPD.

If the base, terminals, or surrounding components show heat or arc damage, the complete assembly should be investigated.

Why does my SPD keep turning red?

Repeated failure can indicate more than ordinary surge aging.

考えられる原因は以下の通り：

• repeated severe surges,
• incorrect SPD voltage rating,
• temporary overvoltage,
• incorrect application,
• installation problems,
• grounding problems,
• inappropriate backup protection,
• excessive environmental stress.

If cartridges repeatedly fail at the same location, investigate the system instead of continuing to replace modules without identifying the cause.

Can an SPD last forever if the indicator stays green?

No reliable fixed lifetime can be determined from indicator color alone.

SPD life depends on the electrical stress it experiences, environmental conditions, product design, and installation.

The indicator should be treated as one part of a wider inspection and maintenance process.