SPD Type 1 vs Type 2 vs Type 3

Surge Protective Device Type 1 vs Type 2 vs Type 3

Created by: Glen Zhu | Updated Date: February 2nd, 2024

SPD Type 1 vs Type 2 vs Type 3

What is Type 1, Type 2, and Type 3 SPD Surge Protective Device?

SPD concept: Surge Protective Device (SPD) is an electrical appliance designed to protect circuits and associated facilities from damages caused by transient overvoltages and spikes. They can provide precise protection to minimize equipment downtime and guarantee smooth operation.

Type 1 Surge protective device: Type 1 SPD, also known as Class I SPD, installed at the service entrance of an electrical system, is designed to withstand high-energy surges, protecting severe transient events for equipment and circuits within the electric system.

Type 2 Surge protection device: Type 2 SPD, or Class II SPD, is typically installed downstream from type 1 or at distribution panels. It offers protection against residual surges and lower-energy transients, working in combination with the type 1 surge protective devices.

Type 3 Surge protector device: Type 3 SPD, or Class III SPD, is installed at the point of use, near or within significant or sensitive individual devices, providing accurate and localized surge suppression against low-energy surges that is relatively minor but may enough to damage specific equipment as well.

Differences between Type 1, Type 2, Type 3 SPD surge protector


Different SPDs are categorized and rated based on specific waveforms that simulate the nature of common electrical disturbances.

A waveform refers to the specific shape and characteristics of the transient voltage or current surge that the SPD is designed to withstand. Different types of SPDs are tested and rated against different waveform standards, which represent different types of potential surges. Here are some of the most common:

10/350 µs Waveform (Type 1 SPDs): features a rise time of 10 microseconds and a more protracted duration of 350 microseconds. The waveform is employed in defining the ratings of type 1 SPDs, specialized devices crafted to protect against direct lightning strikes. The extended rise time reflects the slower buildup of voltage typical in such lightning events.

Figure 1 – Iimp 10/350 µs Waveform of Type 1 Surge Protective Device SPD

8/20 µs Waveform (Type 2 SPDs): This waveform exhibits a rapid rise time of 8 microseconds and a relatively extended duration of 20 microseconds. It is a standard for defining the ratings of type 2 SPDs. The devices are engineered to protect against fast-rising, high-current surges that may arise from activities like switching operations or nearby lightning strikes. The waveform effectively replicates the swift increase in voltage associated with these events, guiding the design and performance expectations of type 2 SPDs.

Figure 2 – In and Imax 8/20 µs Waveform of Type 2 Surge Protective Device SPD

For protection of signal or data lines, the 1.2/50 µs Waveform is indispensable. Characterized by an extremely fast rise time of 1.2 microseconds and a brief duration of 50 microseconds, this waveform is utilized in defining the ratings of SPDs designed for safeguarding signal and data lines. Signal and data lines are highly sensitive to rapid voltage changes, and this waveform simulates a very fast-rising, lower-current surge often encountered in these applications.

Figure 3 – Uoc 1.2/50 µs Waveform of Type 3 Surge Protective Device SPD

Energy Handling Capacity:

Three types of SPDs differently in their energy handling capacity as they are designed to function against varied end-of-use scenarios, classified according to their location and protection level:

Type 1 surge protective device (SPD), categorized as Class B, efficiently handles the highest surge currents originating from direct lightning strikes or intense high-energy events, with an energy handling capacity of Iimp (10/350 µs) 25kA to 100kA.

Type 2 surge protective device (SPD), classified as Class C, addresses medium-sized surges more common than type 1 but still potent enough to damage electronics. With an energy handling capacity ranging from In & Imax (8/20 µs) 20kA to 75kA.

Type 3 surge protective device (SPD), classified as Class C, specializes in handling the smallest surges from switching transients within the building’s electrical system. Operating with an energy handling capacity of Uoc (1.2/50 µs) 6kV to 20kV.

Is Type 1 SPD better than Type 2?

A type 1 SPD is generally crafted to manage the high-energy surges linked with direct lightning strikes. However, type 1 arresters alone do not fully protect the electrical system. From the standpoint of energy handling capacity, they do surpass that of type 2 SPDs, whereas type 1 SPDs confront greater surge currents. Although they can endure a significant portion of the energy, there remains residual current that requires the functionality of type 2 surge arresters.

Consider a large concert venue where the main entrance is equipped with sufficient security checks (functions as a type 1 SPD) to prevent any major threats or unauthorized items from entering the venue. At the same time, inside the concert hall, there are additional security personnel and checks (similar to a type 2 SPD) to handle smaller issues to guarantee the concert is going on smoothly.

The choice between type 1 and type 2 SPDs depends on factors such as installation location and the anticipated energy currents they need to handle. It’s worth noting that neither type 1 nor type 2 SPDs are inherently superior; their effectiveness is contingent on specific application requirements.

Positions type 1 and type 2 SPDs are designed to protect

Type 1 SPDs are strategically designed to be installed at the main electrical panel and their primary function is to handle high-energy surges that originate externally.

Type 1 Surge Protective Devices are intended for installation between the secondary of the service transformer and the line side of the service equipment overcurrent device, as well as the load side, including watt-hour meter socket enclosures, and are intended to be installed without an external overcurrent protective device.

It will be installed in the primary distribution board at the origin of the electrical installation. Type 1 surge protection device is particularly useful in a high lightning density area where the risk of heavy surge current or even direct strike is high (eg.: buildings equipped with lightning rods).

Type 1 surge protective device (SPD) can be found extensively in various applications, prominently at the main electrical panel.

Figure 4 – Type 1 surge protective device (SPD) FLP25 series for electrical AC distribution board panel box switchboard cabinet enclosure

On the other hand, type 2 SPDs are positioned at the sub-panel or branch circuit level within the electrical system and on the load side of the service equipment overcurrent device, including SPDs located at the branch panel. They are designed to provide protection against localized surges and moderate to high-energy transients that may still pose a threat to sensitive equipment.

By being closer to the point of use, type 2 SPDs offer a secondary layer of defense, effectively preventing surges from traveling further into the electrical network.

The device would normally be installed in sub-distribution boards and in the primary distribution board if there was no requirement for a type 1 surge protective device.

Figure 5 – Type 2 surge protective device (SPD) SLP40 series for electrical AC distribution board panel box switchboard cabinet enclosure

Which types of SPD do you need? Type 1, Type 2 or Type 3

Choosing the right types of SPD depends on multifaceted factors related to the specific characteristics and risks associated with your electrical system.

When it comes to industrial sites, advanced plants, or residential house and buildings exposed to lightning strikes that require serious surge protection, type 1 surge arresters emerge as the indispensable option. They are designed to handle extreme energy that without protection would severely damage the whole system and facilities there connected, which could potentially result in operational downtime or even fire incidents.

Type 1 surge protective device (SPD) is the most effective in withstanding the formidable energy unleashed during lightning strikes and other high-energy electrical surges.

If you are protecting electrical systems that have a lower susceptibility to lightning strikes and electrical disturbances, coupled with a relatively moderate circuit load, then type 2 surge protective device can be a great choice.

The selection of type 2 SPDs becomes particularly advantageous in scenarios where the primary concern lies in managing localized surges and moderate-energy transients.

For single and sensitive electrical eqipment such as PCs, televisions, chargers and meters, etc. Filtered by type 1 and type 2 SPDs installed upstream, the surge energy is greatly minimized, whereas there is still residual energy that can pose a threat to the sensitive devices.

Installed at outlets or near the specific terminal equipment, type 3 SPDs are specialized for the point-of-use protection that offer accurate surge protetion for individual electronic equipment and appliances from lower-level surges that may originate within the immediate vicinity.

In addition to commonly used SPDs mentioned above, specialized devices cater to specific surge protection needs for various applicance. Examples include PoE (Power over Ethernet) surge protector, data and signal line arresters, LED surge protector. Combined with type 1 and type 2 devices, together they establish a comprehensive surge protection system that contributes to normal operation.

Should I get both Type 1 and Type 2 SPDs?

The decision to use both type 1 and type 2 SPDs depends upon various factors. Considerations include the risk of lightning strikes in the area, the sensitivity of the electronic equipment being used, budget plans, and adherence to local electrical codes and regulations.

In situations where the risk of lightning is high or where critical and sensitive equipment is in use, the installation of both types of SPDs is often recommended.

Type 1 surge arresters are required to be installed directly under the incoming breaker, especially when there is a lightning rod on the building roof.

For industrial and commercial sites, it is a must to have both surge arresters installed in place as lightning protection to these areas dense in popularity comes more urgent, the lack of protection could not only bring in equipment and facility damage but potentially extend to putting the safety of people at risk.

Consulting with a qualified electrician or electrical engineer is necessary to assessing the specific needs of the electrical system and determining the most effective combination of SPDs for sustained protection.

What is the benefit of cascading / layering Type 1 and Type 2 SPDs in an electrical system?

Cascading or layering type 1 and type 2 Surge Protective Devices (SPDs) in an electrical system is a strategic approach that creates a tiered defense system against surges of varying intensity.

The primary benefit lies in the comprehensive protection it offers. Type 1 SPDs, positioned at the service entrance, are designed to divert high-energy surges. Combined with type 2 SPDs at distribution or branch panels within the facility, the comprehensive system is protective against both high-energy and low-level surges.

Another significant advantage is the redundancy in surge protection it brings. In the event that the type 1 SPD at the service entrance encounters overwhelming surges or experiences a failure, the type 2 SPDs act as a backup, delivering continued protection and resilience for the electrical system.

The strategic setting also brings localized protection to specific sensitive devices and equipment within the building that is located far from the main service entrance.

By employing a cascading approach, stress on the type 1 SPD is greatly reduced as the type 2 SPDs downstream share the load. This distribution of responsibility can extend the lifespan and effectiveness of the primary SPD.

It is worth noting that type 1 and type 2 SPDs are not the sole options for a cascading surge protection system. It is feasible and recommended to introduce various other types of SPDs into the system, such as type 3 SPDs, PoE SPDs, LED SPDs. The inclusion of different types of devices enhances the comprehensiveness of the system, which can lead to optimal performance of surge protection.

However, the specific cascading approach lies on requirements of each electrical settings as blindly employing a vast array of devices doesn’t necessarily equal to improved protective effects.

Type 1 and Type 2 SPD: installation and rules

Important notes before installing:

  • Make sure power at the circuit breakers or disconnect switches is disconnected.
  • The installation and wiring procedures must adhere to both national and local electrical standards.
  • Qualified licensed technicians or electricians should be responsible for the installation and servicing of the system.

From BS 7671: 2018, 18th Wiring Regulations, the wiring and cables of SPDs mounting can be concluded as follows:

  • The conductor lengths should be as short and straight as possible for best performance.
  • Avoid coiling excess wire. Avoid coiling excess leads.
  • Avoid 90 degrees bend and bend wires as rounded for the best performance.
  • Cut all leads to the correct length.
  • The conductors for the SPD installation are preferably not exceed 0.5 meters and, under no circumstances, surpass 1 meter.
  • For Type 1 SPDs, the live and neutral cables should have a cross-sectional area exceeding 6 mm², while the earth cable should meet a minimum requirement of 16 mm².
  • For Type 2 SPDs, the live and neutral cables should have a cross-sectional area greater than 2.5 mm², and the earth cable should surpass a minimum of 6 mm².

Figure 6 – Type 1 surge protective device (SPD) FLP12,5 series for electrical AC distribution board panel box switchboard cabinet enclosure

Figure 7 – Type 2 surge protective device (SPD) SLP40 series for electrical sub-distribution board panel box switchboard cabinet enclosure

Overcurrent Protective Device:

When incorporating Surge Protective Devices (SPDs), the necessity for an OCPD backup is contingent upon two primary factors:

  • The main OCPD rating of the distribution board.
  • The backup OCPD rating of the SPD.

If the main OCPD is less than or equal to the recommended maximum backup OCPD of the SPD, there is no need for an additional OCPD for the SPD.

Conversely, if the main OCPD rating exceeds the maximum backup OCPD rating of the SPD, the installation requires a backup OCPD. In such cases, it is imperative to install a backup OCPD, and the recommended maximum backup OCPD should be followed.

Figure 8 – Overcurrent protective device installation

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