What is an SPD?

Surge Protective Devices (SPD) are used to protect the electrical installation, which consists of the consumer unit, wiring and accessories, from electrical power surges known as transient overvoltages.

They are also used to protect sensitive electronic equipment connected to the installation, such as computers, televisions, washing machines and safety circuits, such as fire detection systems and emergency lighting. Equipment with sensitive electronic circuitry can be vulnerable to damage by transient overvoltages. The effects of a surge can result in either instant failure or damage to the equipment only evident over a longer period of time. SPDs are usually installed within the consumer unit to protect the electrical installation.

Whenever a sudden increase in current or voltage is produced in the electrical circuit or communication circuit as a consequence of outside interference, the surge protection device may conduct and shunt in a very short period of time, preventing the surge from damaging other devices in the circuit.

Surge protective devices (SPDs) are a cost-effective method for preventing outages and enhancing system reliability.

They are typically installed in the distribution panels and play an important role in ensuring the smooth and uninterrupted operation of electronic devices in a wide range of applications by limiting transient overvoltage.

SPD Types

Classification of SPD Type relates to the tests the device must be able to meet. The test requirements for SPDs for power systems shall comply with EN 61643-11:2012+A11:2018 Low­ voltage surge protective devices. Surge protective devices connected to low-voltage power distribution systems. Requirements and test methods.

There are three classes of tests. The introduction to EN 61643- 11:2012+A11:2018 advises that the Class I test is intended to simulate partial conducted lightning current impulses, while the Class II and Class III tests involve impulses of shorter duration.

Class I tests are carried out with a 10/350 µs current impulse (Clause E.5 of EN 623051:2011). This represents a standard lightning impulse.

For Class II, tests are carried out with the nominal discharge current In 8/20 µs voltage impulse.

For Class III, tests are carried out with a 1.2/50 µs voltage 8/20 µs current combination wave generator.

An SPD may be classified according to more than one test class. Where this is the case, the tests required for all declared test classes shall be applied to device.

Type 1 SPDs

Type 1 SPDs, meeting test Class I, are designed to divert high surge currents associated with direct lightning strikes to earth safely and limit the transient overvoltage to prevent damage to the installation wiring and connected equipment. They also protect against risks to human life.

Where protection against high surge currents associated with direct lightning strikes is required, for example when a building has a structural Lightning Protection System (LPS) or an overhead line at risk of direct strike, Type 1 power SPDs should be installed as close as possible at each origin or point of entry of an electrical service into the electrical installation.

Type 2 SPDs

Type 2 SPDs, meeting test Class II, when located at the origin of the electrical installation address the risk of overvoltage arising from an indirect lightning strike, limiting the transient overvoltage to levels which are safe for connected equipment. Such an arrangement is suitable for installations in locations where direct lightning strikes are unlikely, such as in built-up urban areas.

Where an installation does not have a LPS installed and does not require protection against the effects of direct lightning, a Type 2 SPD shall be installed as close as possible to the origin(s) of the electrical installation.

In industrial installations, Type 2 SPDs may be installed in sub-distribution boards or close to the equipment to be protected, downstream from Type 1 and/ or Type 2 SPDs installed at the origin of the installation.

Type 3 SPDs

Sensitive equipment within the installation may benefit from protection provided by a Type 3 SPD in addition to that provided by Type 1 and/or Type 2 SPDs.

It should be noted that Type 3 SPDs should only be installed in installations where Types 1 and/or 2 SPDs are present upstream of their intended position.

They may be installed within sub-distribution boards (typically Type 2+3 SPDs), near or within items of equipment deemed susceptible to damage from overvoltage, or in fixed socket-outlets or mobile socket-outlet trailing leads.

Type 3 SPDs may also protect equipment from switching transients originating from within the premises.

Combined Type SPDs (e.g. Type 1+2, Type 1+2+3, Type 2+3)

An SPD may be classified according to more than one test class (for example, test Class I (Tl) and test Class II (T2)). In this case, the tests required for all declared test classes shall be performed.

Type1+2 SPDs are installed close to the intake position, such as at the first distribution board, in buildings which are at risk of direct lightning strike having a lightning protection system and/or are fed by an overhead line.

What are transient overvoltages?

Transient overvoltages are defined as short duration surges of electricity which occur due to the sudden release of energy previously-stored or induced by other means. Transient overvoltages can be either naturally occurring or man-made.

In electrical distribution systems, transient voltages occur due to a sudden increase in the amplitude of the voltage or current of the circuit. It is also known as spikes or voltage surges.

These voltage fluctuations can be caused by lightning strikes, switching operations, or the operation of large motors due to high inrush starting current or other equipment.

Transient by lightning strike: One common type is a lightning transient, which occurs when lightning strikes nearby electrical lines or equipment. This can cause a sudden spike in voltage, which can damage equipment and cause power outages.

Transient by switching operation: Another type of transient voltage is called a switching transient, which occurs when a large electrical load is switched on or off. This can cause a sudden surge in voltage, which can damage nearby equipment.

Therefore, surge protection equipment is required in electrical systems to lessen the effects of transient voltage, they redirect excess voltage away from the connected system.

Why Do We Need Surge Protective Devices?

Surge protective devices (SPDs) are essential in protecting electronic equipment from the harmful effects of transient overvoltage that can cause damage, system downtime, and data loss.

In many cases, the cost of equipment replacement or repair can be significant, particularly in mission-critical applications such as hospitals, data centers, and industrial plants.

Circuit breakers and fuses are not designed to handle these high-energy events, making additional surge protection necessary.

While SPDs are specifically designed to divert transient overvoltage away from the equipment, protecting it from damage and prolonging its lifespan.

In conclusion, SPDs are essential in the modern technological environment.

How Does Surge Protective Device Work?

The basic principle behind SPDs is that they provide a low impedance path to ground for excess voltage. When voltage spikes or surges occur, SPDs work by diverting the excess voltage and current to the ground.

In this way, the magnitude of the incoming voltage is lowered to a safe level that doesn’t damage the attached device.

To work, a surge protection device must contain at least one non-linear component (a varistor or spark gap), which under different conditions transitions between a high and low impedance state.

Their function is to divert the discharge or impulse current and to limit the overvoltage at the downstream equipment.

Surge protection devices function under the three situations listed below.

A. Normal Condition (absence of surge)

In case of no surge conditions, the SPD has no impact on the system and acts as an open circuit, it remains in a high impedance state.

B. During voltage surges

In case of voltage spikes and surges, SPD moves to the conduction state and its impedance decreased. In this way, it will protect the system by diverting the impulse current to the ground.

C. Back to normal operation

After the overvoltage has been discharged, SPD shifted back to its normal high impedance state.

How to Choose the Ideal Surge Protective Device?

Surge Protective Devices (SPDs) are essential components of electrical networks. However, choosing a suitable SPD for your system might be a difficult issue.

Maximum continuous operating voltage (UC):

The rated voltage of SPD should be compatible with the electrical system voltage to offer appropriate protection to the system. A lower voltage rating will damage the device and a higher rating will not divert transient properly.

Response Time:

It is described as the time of SPD reacts to the transients. The quicker SPD responds, the better the protection by the SPD. Usually, Zener diode based SPDs have the fastest response. Gas-filled types have a relatively slow response time and fuses and MOV types have the slowest response time.

Nominal discharge current (In):

SPD should be tested at 8/20μs waveform and the typical value for residential miniature-sized SPD is 20kA.

Maximum impulse discharge Current (Iimp):

The device must be able to handle the maximum surge current that is expected on the distribution network to ensure that it does not fail during a transient event and the device should be tested with 10/350μs waveform.

Clamping Voltage:

This is threshold voltage and above this voltage level, SPD starts to clamp any voltage transient that it detects in the power line.

Manufacturer and Certifications:

Selecting an SPD from a well-known manufacturer that has certification from an impartial testing facility, such as UL or IEC, is crucial. The certification guarantees that the product has been examined and passes all performance and security requirements.

Understanding these sizing guidelines will enable you to select the best surge protection device for your needs and guarantee effective surge protection.

Installation Rules to Follow

Despite how easy it is to install a surge protector in a power distribution system, it is crucial to follow the appropriate procedures to assure safety and reduce any potential dangers.

Following these steps when installing an SPD in a distribution system:

- Turn off the power: Make sure to shut off the power before beginning any electrical repair and engage off-load isolator to avoid any unwanted event to occur.

- Installation location: Choose an appropriate location for the SPD. For best protection, the SPD should ideally be located as close as feasible to the main breaker. The surge protection device diagram from the manufacturer should be consulted for details on location requirements.

- Mount the SPD: Install the SPD in the desired location on the DIN rail. Verify that the mounting screws are firmly in place.

- Connecting to the earth connection: In accordance with the manufacturer’s recommendations, ground the SPD. Typically, this requires joining a ground wire from the SPD to the grounding bus bar.

- Test the SPD: Restarting the device after installing the SPD will let you to check that everything is working as it should. For details on particular testing techniques, consult the surge protection device installation manual or the designer’s instructions.

Only electricians with a license or other technicians with the necessary education and training should install SPDs.

To maintain continuous security, the SPD should also go through routine testing and maintenance.

What Causes Surge Protective Devices (SPD) Failure?

Surge protective devices (SPDs) are engineered to provide reliable protection against transient overvoltages, but certain factors can lead to their failure. Following are some of the underlying reasons behind SPDs failure:

Excessive power surges:

One of the primary causes of SPD failure is overvoltage, overvoltage can occur due to lightning strikes, power surges, or other electrical disturbances. Make sure to install the right type of SPD after proper design calculations according to location.

Ageing factor:

Due to environmental conditions including temperature and humidity, SPDs have a limited shelf life and might deteriorate over time. Furthermore, SPDs can be harmed by frequent voltage spikes.

Component failure:

SPDs contain several components, such as metal oxide varistors (MOVs), that can fail due to manufacturing defects or environmental factors.

Improper grounding:

For an SPD to operate properly, grounding is necessary. An SPD can malfunction or possibly become a safety concern if it is improperly grounded.

How Much Are Surge Protection Devices?

The cost of a surge protection device may vary depending on the elements mentioned in the subsection above, such as the device’s kind, the desired level of protection, and the application.

The price range for AC SPDs typically lies between $10 and $150 per unit. The type, brand, and features of the particular device affect the pricing.

It is critical to take the necessary amount of protection parameters into account while choosing an SPD. The highest level of protection is provided by a Type 1 SPD, however, it may cost more than a Type 2 SPD.

There might be additional expenses of installation, other than the price of the item itself. To guarantee that the device is placed correctly and adjusted for maximum safety, it is crucial to make sure that the installation is carried out by a certified electrician.

Despite the fact that initially they may appear to be an additional investment, the price of fixing or replacing broken equipment may be far more than the price of setting up an SPD.

Applications of Surge Protection Devices

Surge Protection Devices (SPDs) find extensive applications in a wide range of industrial, commercial, and domestic areas. They protect electrical and electronic equipment against voltage surges and transients that can damage or degrade their performance.

Low voltage SPD for industrial, commercial, residential:

In industrial settings, Low Voltage SPDs are commonly used to protect sensitive equipment such as computer systems, PLCs, and other electronic devices against surges and transients. These SPDs are also used to protect motors and other heavy machinery from power surges and voltage spikes. Commercial areas such as shopping malls also rely on Low Voltage SPDs to protect critical equipment against electrical disturbances. SPDs are installed in residences to safeguard electronic devices such as computers, TV, and home appliances from voltage surges.

SPD for EV charging application:

In the emerging market of Electric Vehicle (EV) charging applications, SPDs play a critical role in ensuring the safety and reliability of EV charging systems. These SPDs protect the charging station from voltage spikes and surges that can damage the equipment and pose a safety risk to users. In the emerging market of Electric Vehicle (EV) charging applications, SPDs play a critical role in ensuring the safety and reliability of EV charging systems. These SPDs protect the charging station from voltage spikes and surges that can damage the equipment and pose a safety risk to users.

SPD for solar photovoltaic applications:

Photovoltaic applications also require SPDs to protect against lightning strikes and other electrical disturbances that can damage or degrade the performance of solar panels and other components in the system. SPDs are installed between the solar panels and inverters and between the inverters and the grid.