A surge protective device, also known as a surge protector or SPD, is designed to safeguard electrical components against surges in voltage that might happen in the electrical circuit.

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.

An SPD works by diverting excess voltage from transient surges away from the protected equipment. It typically consists of metal oxide varistors (MOVs) or gas discharge tubes that absorb the excess voltage and redirect it to the ground, thereby protecting the connected devices.

Power surges can occur due to a variety of reasons, including lightning strikes, electrical grid switching, faulty wiring, and the operation of high-powered electrical equipment. They can also be caused by events happening inside a building, such as the startup of motors or the switching on/off of large appliances.

Installing an SPD can provide several benefits, including:

Protection of sensitive electronic equipment from damaging voltage surges.

Prevention of data loss or corruption in computer systems.

Extension of the lifespan of appliances and equipment by protecting them from electrical disturbances.

Reduction of the risk of electrical fires caused by power surges.

Peace of mind knowing that your valuable equipment is safeguarded.

The lifespan of an SPD can vary depending on factors like its quality, the severity of surges it encounters, and the maintenance practices. Generally, SPDs have a lifespan ranging from 5 to 10 years. However, it is recommended to regularly inspect and test SPDs and replace them as needed to ensure optimal protection.

The need for SPDs may vary depending on factors like geographical location, local regulations, and the sensitivity of the connected electronic equipment. It is advisable to consult a qualified electrician or electrical engineer to assess your specific needs and determine if an SPD is necessary for your electrical system.

A few common surge-protective components used in manufacturing SPDs are metal oxide varistors (MOVs), avalanche breakdown diodes (ABDs – formerly known as silicon avalanche diodes or SADs), and gas discharge tubes (GDTs). MOVs are the most commonly used technology for the protection of AC power circuits. The surge current rating of an MOV is related to the cross-sectional area and its composition. In general, the larger the cross-sectional area, the higher the surge current rating of the device. MOVs generally are of round or rectangular geometry but come in a plethora of standard dimensions ranging from 7 mm (0.28 inch) to 80 mm (3.15 inch). The surge current ratings of these surge protective components vary widely and are dependent on the manufacturer. As discussed earlier in this clause, by connecting the MOVs in a parallel array, a surge current value could be calculated by simply adding the surge current ratings of the individual MOVs together to obtain the surge current rating of the array. In doing so, consideration should be given to coordination of the operating.

There are many hypotheses on what component, what topology, and the deployment of specific technology produces the best SPD for diverting surge current. Instead of presenting all of the options, it is best that the discussion of surge current rating, Nominal Discharge Current Rating, or surge current capabilities revolve around performance test data. Regardless of the components used in the design, or the specific mechanical structure deployed, what matters is that the SPD has a surge current rating or Nominal Discharge Current Rating that is suitable for the application.

The current edition of the IET Wiring Regulations, BS 7671:2018, states that unless a risk assessment is carried out, protection against transient overvoltage shall be provided where the consequence caused by overvoltage could:

Result in serious injury to, or loss of, human life; or

Result in interruption of public services and/or damage to cultural heritage; or

Result in interruption of commercial or industrial activity; or

Affect a large number of co-located individuals.

This regulation applies to all types of premises which include domestic, commercial and industrial.

Whilst the IET Wiring Regulations are not retrospective, where work is being carried out on an existing circuit within an installation which has been designed and installed to a previous edition of the IET Wiring Regulations, it is necessary to ensure the modified circuit complies with the latest edition, this will only be beneficial if SPDs are installed to protect the whole installation.

The decision on whether to purchase SPDs is in the hands of the customer, but they should be provided with enough information to make an informed decision on whether they wish to omit SPDs. A decision should be made based on safety risk factors and following a cost evaluation of SPDs, which may cost as little as a few hundred pounds, against the cost of the electrical installation and equipment connected to it such as computers, TVs and necessary equipment, for example, smoke detection and boiler controls.

Surge protection could be installed in an existing consumer unit if appropriate physical space was available or, if enough space was not available, it could be installed in an external enclosure adjacent to the existing consumer unit.

It is also worth checking with your insurance company as some policies may state that equipment must be covered with an SPD or they will not payout in the event of a claim.

The grading of the surge protector (commonly known as lightning protection) Is assessed according to the IEC 61643-31 & EN 50539-11 subdivision lightning protection theory, which is installed at the junction of the partition. Technical requirements and functions differ. The first-stage lightning protection device is installed between the 0-1 zone, high for the flow requirement, the minimum requirement of IEC 61643-31 & EN 50539-11 is Itotal (10/350) 12.5 ka, and the second and third levels are installed between the 1-2 and 2-3 zones, mainly to suppress the overvoltage.

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.

SPD Working Principle

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.

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.

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:

1.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.

2.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.

3.Configuration issues

Misconfigured, such as when a wye-configured SPD is linked to a load that is connected via a delta. This may expose the SPD to greater voltages, which could result in SPD failure.

4.Component failure

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

5.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.