Surge Protection Device – Pros and Cons

Surge Protection Device - Pros and Cons

Created by: Glen Zhu | Updated Date: Feburary 24TH, 2024

SPD - Pros and Cons

What is power surges and voltage spikes?

A power surge and voltage spike are both terms that refer to a sudden, temporary increase in electrical voltage but they are slightly differ in duration and magnitude.

A power surge is an abnormally high voltage lasting for a short period of time. A voltage spike is a specific type of power surge characterized by a rapid and brief increase in voltage.

A power surge is a temporary increase in voltage on a power line that lasts for at least three nanoseconds, while a power spike is a very short pulse of energy on a power line that lasts for one or two nanoseconds.

Figure 1 – Power surge transient overvoltage

Power surges typically have less voltage than power spikes, usually 10% to 35% above the normal line voltage, and can last from 15 milliseconds up to several minutes. Power spikes, on the other hand, can contain very high voltages, up to and beyond 6000 volts, but usually last only a short duration of time.

Power surges are often caused by electrical overload, bad wiring, power restoration after an outage, or utility company issues, while power spikes are often caused by lightning strikes. Both power surges and voltage spikes can potentially damage electronic devices and appliances, and surge protectors can be used to protect against them.

Figure 2 – Voltage Spikes and Transients

What is a Surge Protection Device?


A surge protection device (SPD), is an electronic equipment that acts as a shield for your electrical systems and devices against power surges and voltage spikes.

When there is a sudden surge of current or voltage in the power circuit or communication line due to external interference, the surge protection device can quickly conduct and divert the surge, thereby preventing damage to other devices in the circuit.

Surge protection devices are used in various settings to protect against indirect lightning, direct lightning impact, or other transient overvoltage electrical surges. They apply to the surge protection requirements in residential homes, the tertiary sector, and industrial areas.

The purpose of surge protection devices

The concept of lightning protection is first put forward as a response to the destructive and unpredictable nature of lightning strikes. Benjamin Franklin’s famous kite experiment in 1752 contributed significantly to people’s understanding of lightning and led to the invention of the lightning rod, a key development in lightning protection.

As people’s increasing reliance on electrical equipment, it is found that there is necessity to protect expensive electronic devices from damaging electrical surges. Then, we began the history of surge protection devices.

The evolution of surge protection devices has been marked by continuous advancements and improvements to enhance their effectiveness in safeguarding electronic and electrical equipment.

The purpose of surge protection devices is to address the challenges posed by transient voltage events and ensure the reliable protection of electronic and electrical systems in an increasingly connected world.

Features of surge protection devices

Knowing the basics of surge protection devices is an important step to get into the world of surge protection. Surge protection devices typically have several key features designed to effectively protect electronic and electrical equipment from transient voltage spikes and surges. Some common features include:

Voltage Clamping: SPDs are designed to clamp excessive voltage to a safe level, preventing it from reaching connected devices.

Response time: SPDs have a fast response time, reacting quickly to voltage surges to divert or suppress the excess energy before it can cause damage.

Energy Handling capacity: The ability of an SPD to handle and dissipate a specific amount of energy is a crucial feature. This is often expressed in joules and indicates how much surge energy the device can absorb.

Multiple Mode Protection: SPDs may provide protection against different modes of surges, such as common mode (line-to-ground) and normal mode (line-to-line), ensuring comprehensive protection.

Thermal Protection: Many SPDs include thermal protection mechanisms to prevent overheating during prolonged or severe surge events.

Compatibility: Ensure the SPD is compatible with the type of power line or data line you want to protect. Some are tailored for AC power, while others cater to specific data lines like telephone or network cables.

Why do we need surge protection devices?

The impact of power surges and voltage spikes can be significant, leading to substantial damage and contributing to the failure of electrical equipment. Damage due to electrical surge is one of the leading causes of failure of electrical equipment. The subsequent maintenance costs are often relatively high.

Surge protection is an investment in security. By safeguarding your equipment from these unexpected surges, you’re protecting your bottom line, your operations, and your valuable data.

There is no surge protection device that is 100% effective. However, it could protect against very large surges in most situations. They are designed to provide a level of protection against electrical surges and transient voltage spikes.

Is a surge protection device worth it?

Power surges and voltage spikes can be caused by various factors, both internal and external. Common causes include the restoration of power after an outage, downed power lines, electrical grid malfunctions or accidents, on/off cycling of large appliances, wiring faults, tripped circuit breakers, and lightning strikes.

While very large surges, primarily caused by lightning and temporary interruptions resulting from storm damage, occur infrequently, normal equipment operation may cause surges over 1,000 volts multiple times per day.

The additional voltage generated by both surges and spikes produces excess heat, posing a serious threat to circuit boards and critical components in electronic equipment. Damage can occur abruptly with large surges or spikes, or gradually over time with smaller, repeated occurrences.

It is worth to install a surge protection device to solve power surge and transient over-voltages. Therefore, it’s important to be aware of these causes and take preventive measures to safeguard electrical equipment from potential damage. This is why we need surge protection devices.

How surge protection devices (SPD) work?

Surge protection devices, limit the voltage supplied to electrical devices to a certain threshold by short-circuiting current to ground or absorbing the spike when a transient occurs, and they work by using at least one non-linear component that transitions between a high and low impedance state.

At normal operating voltages, the SPDs stays passive and do not affect the system. When a transient voltage occurs on the circuit, the SPD moves into a state of conduction (or low impedance) and diverts the surge current back to its source or ground.

This limits or clamps the voltage to a safer level. Once the transient is diverted, the SPD automatically resets back to its high-impedance state.

Figure 3 – The operation of surge protection devices

Pros and cons of surge protection devices (SPD)

As we know the importance of surge protection devices, it is worthwhile to delve into further questions. Any differences among various types of surge protection devices? The cost of surge protective devices? And pros and cons of surge protection devices itself?

Types of surge protection devices (SPD)

Surge protection devices could be classified into different types, there are three types of surge protection devices based on its working principle and design features.

Switching surge protection devices (SPD)

Switching surge protection devices also known as short-circuit surge protectors, the natural high impedance flexibly transverse to low impedance when the surge occurs. Components of voltage-switching surge protection devices include discharge gaps, gas discharge tubes, thyristors, and three-terminal bidirectional controllable silicon switch elements.

These surge protection devices control the flow of current by introducing a switch into the circuit. When the voltage exceeds a set threshold, the switch closes, directing the surge current to the ground, thus protecting the connected devices.

Switching-type surge protection devices typically have a fast response time to protect against transient over-voltages, capable of quickly grounding surge currents and high-energy applications. They are suitable for applications that require a rapid protection response, such as those with high demands on equipment.

However, they require external power sources to operate and may produce EMI (electromagnetic interference) and radio frequency interference (RFI) during operation. Additionally, this type surge protection devices are more expensive than other types, and limited for low-energy applications. It is worthing to note that the effectiveness of SPDs can deteriorate over time, becoming less effective.

Clamping surge protection devices (SPD)

This type of surge protection device relies on components (usually varistors or diodes) becoming conductive at a specific voltage. Non-linear components exhibit a unique property: their resistance changes dramatically with voltage.

When normal voltage levels flow through the circuit, the MOVs/diodes offer high resistance, acting almost like open circuits. This means electricity flows minimally through them, allowing your equipment to function unhindered.

However, when a voltage spike occurs, the MOVs/diodes experience a surge of voltage. This triggers a sudden decrease in their resistance, essentially turning them into low-resistance paths. Now, the excess voltage preferentially flows through the SPD instead of your delicate equipment, effectively clamping the voltage at a safe level.

Clamping-type surge protection devices excel in limiting overvoltage and maintaining the voltage at a safe level. They typically start working when the voltage exceeds a specific threshold. Their versatility makes them suitable for various settings, from residential homes to industrial facilities.

With slower response time, they may have lower surge current handling capabilities. MOVs/diodes can gradually lose their effectiveness over time due to repeated exposure to surges. When they fail, they can short-circuit the circuit, requiring immediate replacement.

Combination surge protection devices (SPD)

Combination-type surge protection devices combine multiple protection technologies, often including both switching-type and clamping-type components. This allows for more comprehensive protection, leveraging the rapid response of switching-type components and the voltage-limiting capabilities of clamping-type elements.

Combination-type surge protection devices integrate different types of protection, suitable for applications with high demands on protection performance. Combines the rapid clamping action of MOVs/SADs with the swift diversion of thyristors/MOSFETs, resulting in faster overall protection compared to pure clamping-type SPDs.

Can withstand and safely channel larger surge currents than pure clamping-type SPDs, making them suitable for installations prone to severe surges. Compared to pure switching-type SPDs, the combination approach mitigates electromagnetic interference (EMI) generation during operation.

Combination-type SPDs are generally more expensive than pure clamping-type or switching-type SPDs. Their combined technology makes them more complex than single-technology SPDs. Installation and maintenance may require specialized expertise.

Pros and cons of surge protective devices



Response Time

Response  Stability

Response Dispersion

Residual Current

Leakage Current

Voltage Protection Level


Clamping SPDs

Moderate fast <25ns



Extremely small



Yes, gradually



Moderate slow <25ns



Extremely big




Combination SPDs – series connection








Combination SPDs – parallel connection

MOV is fast

Steady followed by sharp


Extremely big



Yes, gradually

Table 1 – The pros and cons – each type of surge protection devices

Cost of surge protection devices (SPD)

IEC61643 standard strongly recommends to installing surge protection devices for low-voltage power systems. This standard applies to all types of SPDs, including those used in residential, commercial, and industrial installations.

How much do surge protection devices cost? The question is always concerned by people to evaluate whether to equip surge protection devices to protect their buildings from lightning damage.

The key point in assessing the cost-effectiveness of surge protection devices is to weigh the pros and cons that their installation will bring.

It seems that we save a lot of money by cutting down the cost of surge protective device installation the potential loss would far overtake. Any incidents of equipment damage, downtime, data loss could happen when exposed to the threat of surges or transient over-voltages.

With surge protection device vs. Without SPD

The big advantages of surge protection devices lie in their ability to get free from the threat of lightning currents or transient over-voltages, ensuring a long-term stable operation of equipment. But the upstream usually need the coordination of MCB or fuse and is a must for earthing systems.

Surge protection devices prove their benefits in various ways over a long-term running. Our expensive devices and equipment are protected from electrical failures and malfunctions, not only reducing overall maintenance expenses but also prolong their service life.

Besides, the role of surge protection devices in preserving the integrity of critical information becomes more pronounced. Surge protection devices safeguard the data communication and storage for data centers and telecommunication systems, ensuring that data transmitted through phone lines, fiber optics, and other communication channels remains secure.

The potential risks of not using surge protection devices include device damage, data loss, fire hazards, reduced equipment longevity, and potential productivity and revenue loss.

Some risks may occur if unproperly using surge protection devices. If the chosen SPD is not suitable or if it is installed incorrectly, there is a risk of fire hazards. After installation, the surge protector may not function as intended.

There is a risk of increasing the probability of equipment being struck by lightning. If a series-type surge protector is chosen, it may potentially impact the normal operation of related circuits.

Although these risks do exist, under normal circumstances, as long as you follow the instructions and use the protector correctly, these risks can be completely avoided. Therefore, when selecting, installing, and using surge protectors, remember to choose the appropriate model and follow the correct procedures step by step.

The lifespan of surge protection devices (SPD)

The ability of each surge protector to withstand lightning strikes is limited to a certain number of occurrences. If the number of lightning strikes exceeds the designated limit for the surge protector, it will become damaged and require immediate replacement and maintenance.

Surge protectors are susceptible to mechanical damage based on their usage environment. For instance, damage to the protection casing can lead to leakage or water ingress, posing a safety risk in lightning protection.

Any surge protector with damaged casing or unclear markings should be promptly replaced and repaired.

Power surge protectors are typically installed indoors, experiencing less exposure to lightning currents, resulting in a relatively longer lifespan. The usual operational cycle for lightning protection devices is around 5 years, and timely replacement is necessary to ensure effective lightning protection.

In accordance with the lightning protection device testing technical specifications, annual inspections are required for all lightning protection devices.

After the general surge protector’s protection action occurs, it is usually invisible to the naked eye. To determine whether a power surge protector is faulty, degraded, or has been damaged by lightning, it is typically assessed through its indicator window. If the indicator window changes from green to red, it indicates a malfunction in the lightning protection device, and replacement is necessary.

Do cheap surge protection device (SPD) work?

The difference between a cheap and an expensive surge protection device lies in its effectiveness in dissipating lightning currents. The factors that influence effectiveness are the quality of internal components.

Normally, the quality of Metal Oxide Varistors (MOVs) depends on the operation of surge protection devices. Choosing a reliable metal oxide varistor is crucial; considerations such as UL or IEC certification, Joule rating, response time, environmental factors, and warranty should be taken into account.

The certification is also an authoritative factor to consider when determining if a surge protection device is reliable. The concern is that many cheap surge protection devices are not lightning-proof, and the inexpensive MOVs may not withstand transient over-voltages in a very short time. Therefore, when choosing surge protection devices, priority should be given to reliability and safety.

Traditional vs. Upgraded surge protection devices (SPD)

The evolution of surge protection devices has undergone significant advancements over time. Traditional surge protectors, characterized by their susceptibility to filament formation, face challenges in promptly discharging surges to the earth. This limitation can lead to overvoltage, causing potential safety hazards such as fires within the surge protection devices (SPDs).

In response to these challenges, upgraded surge protectors incorporate innovative disconnection mechanisms that effectively isolate and extinguish arcs.

This enhanced design ensures that when surge capacity exceeds the device’s threshold, a trigger mechanism is activated, facilitating the safe dissipation of the surge energy to the ground. The introduction of this unique feature addresses the shortcomings of traditional surge protectors, contributing to improved safety and reliability.

Moreover, the use of quality high-energy MOVs in upgraded surge protection devices has proven to be a valuable enhancement. The quality high-energy MOVs not only increase the service life of the devices but also enable them to better withstand the impact of high surge currents.

This improvement is particularly crucial in environments where frequent or intense surges may occur, ensuring the longevity and sustained effectiveness of the surge protection system.

Surge Protection Device (SPD) - New vs. Traditional

Coordination between surge protection device and its disconnect circuit breaker or fuse

What is a circuit breaker?

A circuit breaker is an electrical safety device that automatically interrupts the flow of current when it exceeds its design limitations, preventing the supply of energy to the loads.

It works like an automatic switch, which has a base current value, switching off the circuit where it was installed whenever this value is exceeded. The circuit breaker contains two different tripping principles to protect the circuit: thermal protection design and magnetic tripping mechanism.

The basic components of a circuit breaker include a tripping or protection mechanism, an operating mechanism, a molded frame, and arc chutes. When the lever of a circuit breaker is switched to the “on” position, it allows electricity to freely flow from the power supply contacts and out the upper terminal to power the loads on a circuit.

A thermal magnetic trip unit’s bimetallic strip overheats in an event such as overload, causing it to bend and open the circuit, automatically cutting off power. Circuit breakers are used in both residential and industrial applications and are available in various sizes, from small devices protecting low-current circuits to large switchgear designed for high-voltage circuits.

Surge protection devices with circuit breaker

Coordination between surge protection devices and circuit breakers is essential for achieving a balance between effective protection and the seamless operation of an electrical system.

Surge protection device and circuit breakers both cut off power during exceptional conditions, but they have different purposes and react to different events. Surge protection devices are specifically intended to protect against voltage spikes and surges, diverting excess voltage away from electronic devices and preventing damage caused by sudden increases in voltage.

While circuit breakers protect wires from starting a fire due to too many amps (amount of electrical current), surge protection devices protect your appliances from power surges, which is a brief spike in voltage (electrical power or force).

A circuit breaker provides protection against overloads in the circuit. If there is an excessive current flow due to an overload, the circuit breaker quickly interrupts the current, preventing damage to wires and devices. While a surge protector is designed to mitigate voltage surges, a circuit breaker ensures comprehensive overload protection.

Circuit breakers also offer protection against short circuits in the circuit. In the event of a short circuit, the circuit breaker rapidly cuts off the current, preventing potential fire hazards and equipment damage. This short circuit protection is not provided by surge protectors.

The overload and short circuit protection offered by a circuit breaker helps safeguard equipment. While a surge protector can reduce the impact of voltage surges, it may not provide complete protection for devices in the case of other faults.

Pros of surge protection devices with SCB

The traditional method is to link a fuse or breaker in series in front of lightning protection devices. However, this approach presents for mismatching aspects.

When lightning protection devices degrade or experience over-voltage in the distribution circuit, lightning protection devices will become short-circuited to grounding and fuses or breakers are unable to disconnect quickly.

During lightning events, fuses or breakers may struggle to withstand the temporary energy of the lightning current, as they were initially designed as components of power distribution. This vulnerability can lead to tripping or explosions, compromising the effectiveness of lightning protection.

When lightning currents go through breakers, the Up value is very high and lightning protection devices may struggle to adequately safeguard equipment. Fuses or breakers may fail to disconnect in the power installed line of the transformer during a short circuit, impeding a quick response to the situation.

The issue of mismatching between surge protection devices and fuses or breakers has been effectively addressed by SCB, preventing the problem of surge protection device failure ignition trips.

The SCB’s breaking capacity exceeds that of standard circuit breakers, providing enhanced protection against electrical surges. Additionally, equipped with a dedicated circuit breaker for surge protection, ensuring that in the event of a fault, the surge protective device can quickly trip, preventing potential damage to the electrical system and connected equipment.

By quickly tripping in response to electrical surges, SCBs help prevent damage to connected equipment and ensure the longevity of electrical systems and devices. It prevents electrical surges from causing fires, offering an additional layer of safety and protection for both residential and commercial electrical systems.

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