Created by: Glen Zhu | Updated Date: April 11th, 2025
In today’s world, modern electrical systems frequently face power surges and voltage irregularities. These issues can damage devices, disrupt operations, and lead to costly repairs. So, how can you ensure your equipment remains protected? The answer is to use an AC Surge Protective Device (SPD). Acting as a strong shield, an AC SPD safeguards devices and ensures the reliability of the electrical system.
Power surges can occur due to various factors, such as lightning strikes, grid fluctuations, or faulty wiring. For instance, in the Philippines, frequent power outages—occurring approximately 32 times a year—highlight the critical need for surge protection. SPD is crucial for protecting valuable data.
Alternating Current (AC) power is the most widely used form of electrical energy in residential, commercial, and industrial power distribution systems around the world. Unlike Direct Current (DC), where electric charge flows in one direction, AC power periodically reverses direction, typically following a sinusoidal waveform.
Most power grids operate at standard frequencies of either 50 Hz or 60 Hz, depending on the region. Additionally, the voltage levels in AC power distribution systems vary globally.
Application | Voltage Level | Frequency |
Residential (EU/Asia) | 230V | 50 Hz |
Industrial | 120V | 60 Hz |
Application | 380V / 400V / 415V | 50 Hz or 60 Hz |
AC power is transmitted over long distances efficiently, but it is highly susceptible to electrical disturbances, especially transient overvoltage, commonly referred to as surges.
A surge, or transient overvoltage, is a sudden, short-duration increase in voltage within an electrical circuit. These surges typically last from microseconds (μs) to milliseconds (ms). Despite their brief duration, they can carry extremely high energy levels that may damage electrical equipment.
Electrical surges can originate from a variety of internal and external sources. Understanding these sources is crucial for implementing effective surge protection strategies.
1. Lightning Strikes
Direct lightning strikes or indirectly induced surges caused by nearby lightning events are the most severe sources of transient overvoltage.
2. Utility Switching Events
Power grid switching operations, capacitor bank switching, and load-shedding can generate switching transients.
3. Electrical Faults
Short circuits, ground faults, and other power system anomalies can cause sudden overvoltage.
4. Switching of Inductive Loads
Motors, transformers, elevators, HVAC systems, and other inductive loads can create switching surges when turned on or off.
5. Electrostatic Discharges (ESD)
Sudden electrostatic discharges from human contact or machinery may induce small surges in sensitive circuits.
6. Internal Equipment Operations
Switching of power factor correction devices, relay operations, or variable speed drives (VFDs) can generate localized transient events.
The Potential Risks of Surges
Surges in AC power systems present serious risks across different environments:
Sector | Impact of Surges |
Residential | Appliance failure, LED light damage, smart home device malfunctions |
Commercial | Computer crashes, data loss, communication interruptions |
Industrial | Equipment downtime, PLC and control system failure, production loss |
Critical Facilities | Medical equipment damage, server downtime, financial system outages |
Surges can damage systems in many ways. They may cause flashovers, corrosion, or harm to sensitive parts like ICs. For example, a ground fault can create short circuits, stopping devices and needing expensive fixes.
Without proper surge protection, even a single transient event can cause irreversible damage. The cost of downtime, repair, or data loss often exceeds the investment in proper Surge Protective Devices (SPDs).
SPDs are designed to provide a safe discharge path for surges, protecting equipment, preserving operational continuity, and enhancing system safety.
SPD (Surge Protective Device) is an essential electrical safety component specifically designed to protect power systems from transient overvoltage, commonly known as surges. These devices act as a critical line of defense by diverting excess surge energy safely to the ground, thereby keeping your system safe and running smoothly.
Surge Protective Devices (SPDs) are categorized into AC (Alternating Current Surge Protective Devices) and DC (Direct Current Surge Protective Devices) types, depending on the nature of the currents they are designed to protect.
AC SPD: Designed to protect systems operating on alternating current (AC), where voltage oscillates sinusoidally at 50-60 Hz (e.g., 230V AC in homes or 480V AC in industrial grids). AC SPDs mitigate surges in power lines connected to utility grids or AC-powered equipment.
In this article, we will focus on AC SPDs only.
An AC SPD is a highly engineered device combining several key components designed for performance and safety:
1. Metal Oxide Varistor (MOV)
MOVs are key components of surge protectors. They soak up extra voltage to keep devices safe. MOVs are primarily composed of zinc oxide (ZnO), accounting for 80-90% of their material. When a power surge happens, the MOV changes how it works. At normal power levels, it blocks electricity. During a surge, it lets electricity flow, sending extra energy away from your devices.
Metal Oxide Varistor (MOV)
MOVs are highly effective at absorbing surge energy and reducing residual voltage. They work well in both computer tests and lab experiments. Tests, such as thermal imaging, demonstrate their ability to withstand repeated surges. But MOVs can wear out after many surges. Regular replacement ensures the continuous effectiveness of the surge protector.
2. Gas Discharge Tube (GDT)
GDTs are another important part of surge protectors. They use a gas-filled tube to deal with big power surges. When a surge hits, the gas inside turns into a conductor. This lets the GDT safely send extra energy away from your devices.
GDTs are highly effective at handling large energy spikes. They are often used in surge protectors for high-energy situations, keeping your electronics safe during big voltage jumps.
Metal Oxide Varistor (MOV)
GDTs and MOVs work together to provide enhanced protection. GDTs handle big surges, while MOVs take care of smaller, more frequent ones. Together, they make sure your surge protector can handle different types of voltage surges. Sharing the work also makes the surge protector last longer.
3. Transient Voltage Suppressor (TVS)
TVSs respond rapidly to suppress voltage surges. They lower the voltage to a safe level, protecting sensitive devices. Unlike MOVs and GDTs, TVSs are made from semiconductors. Their quick action makes them perfect for protecting delicate electronics like computers and phones.
4. Grounding System
The grounding system helps protect electronics from power surges. It provides a safe path for excess electrical energy to dissipate into the ground. During a surge, it moves the extra energy away from your devices. This stops damage to the delicate parts inside your gadgets.
Importance of Grounding Quality
A good grounding makes surge protectors work better. A strong grounding system quickly removes extra energy. Poor grounding may compromise the protective performance of SPDs.
To get the best results, check if your home’s grounding is good. Electricians can test and fix your grounding if needed. Good grounding not only helps surge protectors but also makes your whole electrical system safer.
5. Enclosure
The enclosure is the outer shell of a surge protector. It protects the inside parts, like MOVs, GDTs, and TVSs, from damage. It also blocks dust, water, and other things that could harm the device.
Surge protector enclosures are made from strong materials like plastic or metal. Plastic enclosures are lightweight and corrosion-resistant, making them suitable for residential and office environments. Metal ones are stronger and handle heat better, so they’re used in factories.
Inside the SPD, these components work together to handle extra voltage. If a surge happens, it moves the extra energy away from your devices. This ensures that the electrical system remains protected from surge-related damage.
Understanding the working principle of an AC SPD highlights its importance. Whether for a home, office, or factory, it protects against sudden power surges. It acts like a shield to keep your devices safe.
The operation of an AC SPD can be described in several distinct stages during a surge event:
1. Normal Operation: Under standard AC conditions (e.g., 230V RMS, 325V peak), the SPD remains dormant, with MOVs and GDTs in a high-impedance state, drawing negligible current (<1 µA leakage).
2. Surge Detection: It continuously monitors for overvoltage events. A transient—such as a 10-kA lightning-induced surge—can cause voltage spikes exceeding 6 kV, depending on system impedance. The MOV senses this exceedance past its 275V threshold and activates instantly.
3. Energy Diversion: The MOV’s resistance drops, shunting 8 kA to ground in <25 ns, while the GDT triggers at 600V to handle the remaining 2 kA peak. The grounding path dissipates this energy, limiting voltage across the protected load to <600V.
4. Recovery: After the surge disappears, the AC waveform returns to normal, and the SPD resets to its high-impedance state. If the MOV degrades (e.g., after 100 surges at 10 kA), a thermal fuse disconnects it, triggering an LED indicator to signal the need for replacement. This rapid cycle—often completed in microseconds—prevents damage to downstream equipment.
Well, the truth is — AC SPDs are everywhere around us, quietly protecting the critical electrical systems we all rely on every single day. Let’s break it down by industry to see just how important they are.
Factories and industrial plants are filled with expensive machinery, robots, control panels, and sensitive electronics. Imagine what would happen if a sudden voltage surge struck those systems — production downtime, equipment damage, and, of course, huge financial losses.
That’s why AC SPDs are commonly installed in:
Their job here? Prevent production disruptions and protect costly equipment from electrical damage. In some industries like semiconductor, chemical, or pharmaceutical production, downtime from a surge isn’t just annoying, it can cost thousands of dollars per minute.
Think about office buildings, shopping malls, data centers, hospitals, or airports. These places have loads of electrical and electronic devices — from lighting systems to elevators, HVAC systems to security equipment, and of course, IT infrastructure.
In these environments, SPDs play a crucial role in:
Without SPDs, a single surge could knock out an entire building’s power control system or damage critical IT equipment.
Yes, AC SPDs are also commonly used in homes — residential settings — especially in areas prone to lightning strikes or unstable power supplies.
Why? Because today’s homes are smarter and more electronic-heavy than ever before:
All these gadgets are sensitive to surges. An SPD in the home’s main electrical panel provides peace of mind by safeguarding everything connected to the grid.
Airports, railway stations, metro systems, highway toll booths — they all depend on complex electrical systems for operations, signaling, lighting, and safety.
SPDs here help avoid chaos by:
In Telecom & Data Centers and Renewable Energy Systems, DC SPDs are more widely used than AC SPDs.
Note: Surge protection is needed wherever sensitive devices are used. Installing AC SPDs helps avoid costly damage and ensures smooth operations.
Now that we know what AC SPDs are, how they work, and where they’re commonly used, here comes an extremely important question:
How do you choose the right AC SPD for your project or electrical system?
Step 1: Know Your Power System
Before selecting any SPD, the first thing you need to know is what type of power system you are protecting.
Common AC power systems include:
Power System Type | Features | SPD Requirements |
TN-S / TN-C-S | Neutral and PE separate | Standard SPD |
TT System | Earth independent of neutral | Needs lower Up & higher Iimp |
IT System | No direct earth connection | Special SPD needed |
Tip: Check your power supply diagram or consult an electrical engineer — it’s crucial for proper SPD coordination.
Step 2: Identify the Installation Location (SPD Class)
The location of your SPD decides its “class” or “type” — basically, how strong it needs to be.
SPD Type | Installation Position | Protection Capability |
Type 1 (Class I) | Main power incoming point (near meter) | Withstand direct lightning strikes (high energy) |
Type 2 (Class II) | Distribution boards, sub-panels | Handle switching surges, indirect lightning |
Type 3 (Class III) | Close to sensitive equipment | Fine protection for electronics |
Suggestion: Use consistent formatting like bullet points or arrows:
Type 1 → Type 2 → Type 3 (Layered defense like armor)
Step 3: Look at the Key Parameters of AC SPD
This is where the technical data comes in. Let’s make it simple:
Parameter | Meaning | What to Check |
Uc (Maximum Continuous Operating Voltage) | Maximum voltage SPD can handle without damage | Must be equal to or greater than your system voltage |
In (Nominal Discharge Current) | Current level SPD can repeatedly handle | Higher In means better durability and stability |
Imax (Maximum Discharge Current) | Max surge current SPD can handle once | Directly linked to protection strength |
Up (Voltage Protection Level) | Residual voltage let-through | Should be lower than the equipment’s maximum withstand voltage |
Response Time | Speed of SPD action | Usually in nanoseconds |
Number of Poles | L/N/PE lines to be protected | Depends on system: Single-phase / 3-phase / Neutral |
Step 4: Other Considerations You Can’t Ignore
Here are some often-overlooked but important factors when selecting AC SPDs:
1. Safety Certification
Look for IEC 61643-11 or equivalent standards (like UL, GB)
2. Visual or Remote Indication
SPD failure indicator (green/red window)
Optional remote alarm output
3. Replaceable Modules
Modular SPD = easy to replace damaged parts without rewiring
4. Coordination with Circuit Breaker or Fuse
Proper backup protection (like MCB or fuse) is essential for safe SPD operation.
Consider: Does your SPD require a backup device? What type and rating?
Step 5: Choose Based on Your Application
Application | Suggested SPD Type | Notes |
Industrial plants | Type 1 + Type 2 + Type 3 | Heavy surge environment |
Residential buildings | Type 2 + Type 3 | General protection |
Solar PV systems | DC SPD + AC SPD | Both sides need protection |
Data centers | Type 2 + Type 3 | Sensitive equipment |
Telecom or IT systems | Type 3 near device | Fast response priority |
Quick Example of SPD Selection
Imagine you’re selecting an SPD for a small factory’s incoming AC panel:
| Condition | Recommended SPD |
| Power Supply | 3-phase 400V TN-S system |
| Installation Point | Main panel |
| Suggested SPD | Type 1+2 combined SPD, Uc=385V, Iimp=25kA, Imax=100kA, Up≤ 2.5kV, 4-pole design |
Choosing the right AC SPD isn’t just about the specs — it’s about understanding:
The more you know your project, the easier it is to pick the perfect SPD.
Remember: A well-selected SPD doesn’t just protect your equipment — it protects your investment, your production, your data, and sometimes even your safety.
When it comes to surge protection devices (SPDs), there are many brands available in the market. But why do so many engineers, panel builders, and project owners trust LSP AC SPDs?
The reason is simple — LSP specializes in surge protection, designing products to perform reliably in real-world industrial and commercial environments.
1. LSP is not just an OEM brand. It’s a manufacturer that focuses purely on surge protective technology.
All the SPDs strictly follow the international IEC 61643-11 standard and are built for industrial-grade applications.
In short, LSP knows how to protect your electrical system effectively.
2. Full Range of Products for Various Applications
One of LSP’s biggest strengths is the complete AC SPD product line, which fits into many industries and different installation environments.
Benefit: Modular designs make it easy to combine and expand as needed.
3. Strong Technical Features for Better Protection
Core Technologies:
4. Safety-Focused and Maintenance-Friendly Design
LSP SPDs are engineered with safety and maintenance in mind.
Standard Features:
Protection Level:
5. Complete International Certifications
LSP AC SPDs are certified by multiple global standards, making them trustworthy for global projects.
Ideal for export markets and high-standard project bidding.
6. Market Feedback:
In Conclusion, LSP AC Surge Protection Device — Your Reliable Surge Protection Partner
Key Benefits | Highlights |
Technical Strength | High energy, low voltage, fast response |
Wide Product Range | Full series for multiple scenarios |
Safety Design | Visual status, replaceable modules, remote alarm |
Electrical Performance | Industry-leading specifications |
Value for Money | High quality with reasonable pricing |
Ideal for:
End-users seeking stable and reliable surge protection solutions
Interested in learning more about LSP AC SPD products or getting a quote?
Feel free to contact LSP’s technical team — we’re ready to provide customized surge protection solutions tailored to your project needs.
In today’s world, where electrical systems are becoming more complex and sensitive than ever before, installing a reliable AC Surge Protective Device (SPD) is no longer just an option — it’s a necessity.
Power surges can happen anytime, anywhere — triggered by lightning strikes, grid switching, equipment failures, or even internal disturbances. Without proper surge protection, the consequences can be severe: damaged equipment, downtime, data loss, and significant financial loss.
That’s exactly where AC SPDs step in as the first line of defense.
A well-selected and properly installed AC SPD helps to:
When selecting an AC SPD, it’s essential to consider:
Among various brands available in the market, LSP AC SPDs stand out for their:
Whether for residential buildings, commercial complexes, industrial plants, data centers, or renewable energy systems, LSP provides surge protection solutions that are trusted and proven in real-world applications.
Ready to Protect Your Power System?
Explore LSP’s full range of AC SPDs and discover how our solutions can help protect your projects from costly surge damage.
For product details, technical support, or custom solutions, feel free to contact us anytime!
LSP’s reliable surge protection devices (SPDs) are designed to meet the protection needs of installations against lightning and surges. Contact our Experts!
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