Created by: Glen Zhu | Updated Date: May 12th, 2025
This article was written according to IEC 61643-11:2011 and IEC 61643-12:2020.
Downloads the IEC standards:
Before we discuss lightning and surge protection, we need to understand External Structure Lightning Protection and Internal Structure Surge Protection.
External lightning protection for buildings, which involves preventing direct lightning strikes, is typically composed of a lightning protection system consisting of lightning rods, lightning belts, down conductors, grounding rods, and grounding grids.
Internal lightning protection of buildings, that is, preventing induced lightning, usually includes surge protection in two parts:
The standards of IEC 61643-11:2011 and IEC 61643-12:2020, which we mentioned above, are specifically for low-voltage power supply systems, that is, for this type of surge protection for power supply such as 220Vac, 380Vac, 440Vac.
With regards to surge protection device (SPD) for signals and data lines, it’s according to IEC 61643-21:2012 and IEC 61643-22:2015, we’ll discuss it in the next blog.
IEC 61643-21:2012
Low voltage surge protective devices – Part 21: Surge protective devices connected to telecommunications and signalling networks – Performance requirements and testing methods.
IEC 61643-22:2015
Low-voltage surge protective devices – Part 22: Surge protective devices connected to telecommunications and signalling networks – Selection and application principles.
With regards to surge protection device (SPD) for photovoltaic solar PV DC systems, it’s according to IEC 61643-31:2018 and IEC 61643-32:2017, we’ll discuss it in the next blog.
IEC 61643-31:2018
Low-voltage surge protective devices – Part 31: Requirements and test methods for SPDs for photovoltaic installations.
IEC 61643-32:2017
Low-voltage surge protective devices – Part 32: Surge protective devices connected to the d.c. side of photovoltaic installations – Selection and application principles.
When assessing whether an SPD is needed for an installation, two key factors must be taken into account:
Here is a relatively simple judgment method provided for your reference only. Let’s get started
Before you select the right AC surge protection device SPD, you need determine the country and region you are in what type of system earthing.
Low-voltage power systems are basically characterized by the type of system earthing, Common type of system earthing include: TN-C, TN-S, TN-C-S, TT, IT.
In TN-C system, the neutral and protective earth conductor are combined in a single conductor throughout the system. This conductor is referred to as a PEN, a “Protective Earth & Neutral”. All exposed conductive equipment parts are connected to the PEN.
SPDs installed | Description | Example product |
Phase to PEN (“3+0”) | At least 1.1 x Un |
For example, on a 230 V Ph-N system, Ph-PEN protection should have a Uc rating of at least 255 V. Generally an SPD with a Uc rating of at least 275 V would be selected for 220 to 240 V systems. Often, to allow for power supply voltage fluctuations, a Uc of at least 1.3 x Un is recommended, such as a Uc of 300 V for a 230 V system, or LSP’s unique trigger release technology would be chosen.
Position | LPL | Product Model |
1 | I/II | |
III/IV | ||
2 | ||
3 |
In TN-S system, a separate neutral and protective earth conductor are run throughout. The Protective Earth (PE) conductor is normally a separate conductor, but can also be the metallic sheath of the power cable. All exposed conductive equipment parts are connected to the PE conductor.
In TN-C-S system, the supply is configured as per TNC, while the downstream installation is configured as per TNS. The combined PEN conductor typically occurs between the substation and the entry point into the building, and earth and neutral are separated in the Main Distribution Board. This system is also known as Protective Multiple Earthing (PME) or Multiple Earthed Neutral (MEN). The supply PEN conductor is earthed at a number of points throughout the network and generally as close to the consumer’s point-of-entry as possible.
In TT system, the power supply neutral is earthed at the source (such as at the transformer), while the exposed conductive parts of the electrical installation are connected to a local earth electrode that is independent of the supply earth. There is no direct connection between the system neutral and the protective earth on the consumer’s side.
Position | LPL | Product Model |
1 | I/II | |
III/IV | ||
2 | ||
3 |
In IT system, the power supply has no direct connection to earth, or it is connected through a high impedance. The exposed conductive parts of the installation are connected to a local earth electrode. Because the system neutral is either isolated or impedance-earthed, a single line-to-earth fault does not cause a significant fault current, allowing the system to continue operating without immediate disconnection.
Position | LPL | Product Model |
1 | I/II | |
III/IV | ||
2 | ||
3 |
If you want to learn more about earthing systems, please visit our previous blog https://lsp.global/earthing-systems/
How to choose surge protective devices used for earthing systems in low-voltage electrical power supply systems (IEC/EN System)?
In the IEC/EN system, surge protection devices (SPDs) are tested to various Test Classes, intended to assess and assure their suitability for use in different locations and circumstances. Strictly speaking, the “Class” refers to the type of test, not to the SPD. However, in common usage, surge protection devices (SPDs) are referred to by their Class, for example, a Class I (Type 1) surge protection device is an SPD that has been tested to Class I (Type 1) requirements (of a specified severity), and so on.
Class I / Type 1 – Tested with simulated partial conducted lightning current impulses. These SPDs would be used at points of high exposure, such as where the line close to the SPD might be directly struck by lightning, or at the point of entry to a building fitted with a direct strike Lightning Protection System (LPS).
Class II / Type 2 – Tested with shorter duration current impulses. These SPDs would be installed where the surge currents are expected to be less. This could be at the main power entry point of a building in a non-exposed location (surrounded by taller buildings, for example), or at sub-panels within the building.
Class III / Type 3 – Tested with voltage impulses. These SPDs would be installed at equipment to be protected, and are only expected to handle residual voltages surges that “got past” upstream Class I or II SPDs, and the associated small surge currents. Often, for convenience, Class II protectors are used at these locations as well.
In the illustration above, the type of SPDs installed at the Main Distribution Board, Distribution Boards, and the Equipment to be protected would be as follows:
Surge Protection Device SPD Location categories defined by IEEE standards for surge environments
Building Situation | MDB | DB | Equipment |
Highly exposed, of fitted with LPS | Class I / Type 1 / Class B | Class II / Type 2 / Class C | Class III / Type 3 / Class D |
Less exposed, no LPS | Class II / Type 2 / Class C | Class II / Type 2 / Class C | Class III / Type 3 / Class D |
There are a number of IEC/EN standards that work together to provide a system of classifying the power system, the over-voltages that can occur at different points in the system, the performance and application of surge protection devices (SPDs), and the relative susceptibility of end use equipment to lightning surges. The most directly relevant are the IEC/EN 62305 series standards dealing with both lightning protection and surge protection, and the IEC/EN 61643 series standards covering testing, selection, and application of surge protection devices (SPDs).
Installing surge protection devices (SPDs) at all three levels is not always necessary and depends on factors such as building size and the length of internal wiring. Typically, SPDs are installed at the service entrance, and in smaller installations, additional protection may only be needed at the equipment level. In larger facilities – especially those with multiple floors or extensive layouts – SPDs are commonly installed at distribution boards, with further protection provided for sensitive or critical equipment.
Surge protection devices (SPDs) are mainly classified based on their ability to handle high surge current magnitudes and their effectiveness in clamping voltage during surge events. The key performance parameters include:
SPD Test Class | Parameter | Description |
Class I / Type 1 / Class B | Impulse Current (Iimp) | This current impulse has a 10/350μs waveform |
Class II / Type 2 / Class C | Nominal Discharge Current (In) | This current impulse has a waveform of 8/20 μs, and is nominal because the SPD has to successfully handle a sequence of 15 of these impulses. |
Maximum Discharge Current (Imax) | This current impulse has a waveform of 8/20 μs, and is the maximum 8/20 μs impulse the SPD can handle. It is an optional parameter. | |
Class III / Type 3 / Class D | Open circuit voltage of the combination wave generator (Uoc) | |
All Classes | Voltage Protection Level (Up) |
It is possible to test one surge protection device (SPD) type at more than one Test Class. SPDs are marked and specified with the parameters they have been successfully tested to.
Surge Protection Device (SPD) Classes and Categories
Class I, II and III tested SPDs may be used at the entrance and class II and III tested SPDs may be used for locations close to the equipment
For protection against effects of lightning and against switching overvoltages, class II tested SPDs shall be used.
Where the structure is equipped with a LPS class I tested SPDs shall be used.
Where the structure is not equipped with a LPS and where the occurrence of direct lightning strike to the overhead lines between the last pole and the entrance of the installation is to be taken into consideration, class I tested SPDs at or near the origin of the electrical installation may be also selected.
SPDs shall be installed as close as possible to the origin of the installation and possibly others, if required, close to equipment to be protected.
All these SPDs should be coordinated Oscillation need to be considered as SPD have generally limited protective distance.
Connecting conductors for SPDs shall be as short as possible.
When the Lightning Protection Zone (LPZ) concept is used SPDs should be installed at the zone boundaries.
The installation of SPDs as close as possible to the origin of the installation reduces surge currents flowing through downstream installation device (e.g. meters, terminals, protective devices, switches, etc.).
When the equipment to be protected has a sufficient overvoltage withstand or is located close to the main distribution board, one SPD may be sufficient and should be installed as close as possible to the entrance of the installation. The SPDs should have sufficient surge withstand capability for this location.
SPDs at or near the entrance of the installation shall be connected at least between the following points:
a) If there is a direct connection between the neutral conductor and PE at or near the origin of the installation or, if there is no neutral conductor, between each line conductor and either the main earthing terminal or the main protective conductor, whichever route is shorter;
Note 1: The impedance connecting the neutral to PE in IT systems is not considered as a connection.
b) If there is no direct connection between the neutral conductor and PE at or near the entrance of the installation either: between each line conductor and either the main earthing terminal or the main protective conductor, and between the neutral conductor and either the main earthing terminal or the protective conductor, whichever route is shorter – Connection Type 1 (CT 1), see Figure 1 or between each line conductor and the neutral conductor and between the neutral conductor and either the main earthing terminal or the protective conductor, whichever route is shorter – Connection Type 2 (CT 2), see Figure 2.
Note 2: If a line conductor is earthed, it is considered to be equivalent to a neutral conductor for the application of this subclause.
 |  |
Figure 1 – Connection Type 1 (CT 1) MET: main equipotential terminal Note: Earthing connection of surge protective devices, either (1) and/or (2) should be the shortest route; National regulations may make the use of 1, 2 or both mandatory | Figure 2 – Connection Type 2 (CT 2) MET: main equipotential terminal Note: Earthing connection of surge protective devices, either (1) and/or (2) should be the shortest route; National regulations may make the use of 1, 2 or both mandatory |
After reading the IEC 61643-11:2011 and IEC 61643-12:2020 standards, there are many professional terms and knowledge points.
If you are still completely confused about how to correctly choose a surge protection device. In fact, you don’t need to understand all these technical terms – they will only make it harder for you to make a choice.
LSP – as a professional surge protector device manufacturer, we’ll explain these standards in a simple and easy-to-understand way, guiding you on how to choose the right surge protection device.
Here is a simple way to help you choose the right AC surge protection devices (SPDs) in different locations.
Before you start to select AC surge protection devices (SPDs), you need determine your power supply system is single phase or three phase, and the working voltage. I think this is an easy thing.
Here we take a three-phase and 230VAC power supply system for example.
A Type 1 Surge Protective Device (SPD) can be used in the distribution box below the transformer, inside a compact substation (box-type transformer), or in a power distribution cabinet.
Here is three Type 1 surge protector devices (SPDs)
You may be confused, which of the three Type 1 surge protector devices should you choose?
The upstream dedicated disconnector of an SPD (Surge Protective Device) is a protective device – typically a fuse or circuit breaker – installed between the SPD and the power supply to:
At this main incoming distribution box, if the main air circuit breaker is 3200 A, the upstream dedicated disconnector of Type 1 SPD should use a 100~200 A circuit breaker or a 250~315 A fuse.
The cross-sectional area of the live and neutral wires should be 6 mm² or above, and the grounding wire should be 16 mm² or above.
The total length of the connections for L1, L2, and L3 should be less than 50 cm (50 cm installation rule respected).
If you want to learn more about the Coordination between the surge protective device and the upstream dedicated disconnector of SPD, please visit https://lsp.global/surge-protective-device-coordination/
A Type 1+2 Surge Protective Device (SPD) can be used in the medium-sized distribution box or power distribution cabinet.
Here is three Type 1+2 surge protector devices (SPDs)
At the outgoing distribution box, if main circuit breaker is 250 A, the upstream dedicated disconnector of Type 1+2 SPD FLP12,5-275 series should use a 100~125 A circuit breaker or a 125 A fuse.
The total length of wiring between Type 1 SPD to Type 1+2 SPD should be greater than 5 m.
At the main distribution box, if main circuit breaker rated at 200 A, the upstream dedicated disconnector of Type 1+2 SPD FLP7-275 series should use a 50~80 A circuit breaker or an 80 A fuse.
A Type 2 Surge Protective Device (SPD) can be used in the sub-distribution box.
Here is three Type 2 surge protector devices (SPDs)
At the sub-distribution box, if main circuit breaker rated at 63 A, the upstream dedicated disconnector of SPD should use a 32~40 A circuit breaker or fuse.
At the sub-distribution box, for surge protection of industrial control equipment, the upstream dedicated disconnector of SPD should use a 10~16 A circuit breaker or fuse. SPD can be selected Type 3.
Here is three Type 3 surge protector devices (SPDs)
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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