Aerial view of a housing estate in Ireland

1. Introduction

Dwelling units are consistently under construction in various regions across Ireland. These residential buildings exhibit a variety of dimensions, masonry types, shapes, and house varying numbers of inhabitants. A recurring question arises regarding whether, in Ireland, with its low flash density, do dwelling buildings need to be protected against lightning strikes.

The international standards unequivocally state the importance of conducting a risk assessment to determine the necessity of lightning protection. In numerous cases, considering the characteristics of the building and environment, the inherent risk is low. The conclusive result of the risk assessment often indicates that there is no obligation to install an exterior lightning protection system. Thus, having straightforward rules can obviate the need for conducting complex risk assessment studies for such buildings.

Furthermore, certain equipment such as solar panels and antennas may be installed on the roof. The recurring question is whether these installations should be regarded as integral parts of the system that needs protection. Additionally, it raises the inquiry of whether their presence could alter the overall risk of the building, necessitating additional protection measures.

1.1 Flash Density in Ireland

By definition, the lightning ground flash density (NG) is the number of lightning flashes per square kilometre per year. This value is available from ground flash location networks in many areas of the world.

The flash density value could vary from city to city. There are different recording sources that have issued flash density information, and the duration of recording is different for each of those sources. Table 1 illustrates the maximum value for each different source:

Reference Number of Years of recording Years of recording Maximum Flash Density (km²/year) Remarks
BS EN 62305-2 (2012) 10 Un known 0.08 N/A
Natural Hazards and Earth System Sciences 5 2010 to 2014 0.4 Recorded in Omagh Northern Ireland
Interactive Global Lightning Density Map ( VAISALA Xweather) 7 2016-2022 0.3 Recorded in Omagh Northern Ireland

Table 1: The Maximum Recorded  flash density  in Ireland Country

Based on the provided information, the maximum flash density in Ireland can be assumed to be 0.4, unless there is accessible local information indicating a value greater than 0.4.

2. Scope

This specification defines the minimum requirements for the design, construction, and inspection of lightning protection systems for residential properties located in Ireland. The requirements below apply to new buildings and not to existing ones.

3. Standard and References

3.1 Standards

  • IEC 62305-2: Protection against lightning – Part 2: Risk management
  • IEC 62305-3: Protection against lightning – Part 3: Physical damage to structures and life hazard
  • IEC 62305-4: Protection against lightning – Part 4: Electrical and electronic systems within structures
  • IEC 60364-4-44: Low-voltage electrical installations – Protection for safety – Protection against     voltage disturbances and electromagnetic disturbances
  • IEC60364-5-53: Electrical installation of buildings – Selection and erection of electrical equipment-Isolation, switching and control
  • IEC TR 63227: Lightning and surge voltage protection for photovoltaic (PV) power supply system
  • DIN 18014: Foundation earth electrode- Planning, execution and documentation
  • DIN EN 62305-3: Protection against lightning – Part 3: Physical damage to structures and life hazard
  • I.S.10101: National Rules for electrical installation

4. General

Preliminary evaluation for protection lightning shall be done at basic engineering stage by an independent third party specialised in lightning protection and never by an equipment supplier.

Protection against direct lightning strikes, if assessed to be required, shall be provided by air-termination systems.

Protection against indirect effects, which produce over voltages shall be provided by equipotential bonding and surge protective devices. Equipotentialization is a very important measure to reduce hazard of lightning effects in the space to be protected.

Generally, for regular buildings, a checklist, including the most sensitive equipment to lightning effects, shall be provided. However, this issue is not as critical in residential buildings because equipment failure typically does not pose a risk to human life; rather, it is an economic factor that needs to be investigated by the owner of the building.

If deemed necessary, devices for surge protection against indirect and direct effects of lightning or other transient overvoltage shall comply with IEC 61643.

4.1 Preliminary Evaluation

4.1.1 The Needs of Protection and the Levels of Lightning Protection

For every structure considered, the designer shall decide whether or not a LPS is needed. This subject lies under risk assessment study that has been stated in clause 5 of this specification.

4.1.2 Lightning Protection Zones

After determining that the building needs protection against direct lightning strikes, the volume to be protected shall be divided into Lightning Protection Zones (LPZ) to define different volumes of Lightning Electromagnetic Impulse (LEMP) severity. For residential buildings, two levels, LPZ0 and LPZ1, could be considered. This information is used as input data for performing the risk assessment calculation.

4.1.3 Foundation Electrode System

If the residential building is planned to be constructed in an urban area where space for installing a rod or counterpoise electrode system is limited, the foundation electrode system is always the preferred method for establishing the earth electrode system. Therefore, understanding the appropriate practices for creating a foundation electrode system is crucial. In this regard, Annex II of this specification provides the criteria for designing the foundation earth electrode system. The illustrated flow chart in Annex II is extracted from the DIN 18014 standard.

5. Protection Needs Against Direct Lightning

The need for lightning protection is determined by performing a risk assessment according to IEC 62305-2, which compares the risk value R, as the sum of all the risk components, with the tolerable risk value RT.

5.1 Risk Evaluation

5.1.1 Risk of Loss of Human Life

In General, to minimise the risk of injury to users, the risk of loss of human life (R1) related to the building shall be evaluated by the specialists and compared with the tolerable risk value (RT1). A maximum value of the tolerable risk of loss of human life equal to 10–5 is assumed by this.

According to table 1 , the flash density in Ireland is less than 0.4/km²/year. Consequently, for some residential buildings, the risk of loss of life falls below an allowable limit. To eliminate the need for conducting a risk assessment for each installation, a range of installations has been considered to determine cases where the risk of a direct lightning strike is lower than the tolerable risk. This determination is made using the software provided with [IEC 62305-2]. The following section provides further details.

Note 1:

In the case of a low-risk building, there is no need to assess the risk to human life.

5.1.1.1 Low Risk Building

The building is considered low risk against direct strike if meeting all of the following prerequisites and specific direct strike lightning protection considerations are not needed, include:

  • Domestic dwelling, small business premises or similar low-occupancy building.
  • Moderate size (ground floor area nominally < 800 m)
  • Height less than 15m (typically 4 storeys or less).
  • The number of people not greater than 100
  • Not located on a mountain top which is greater than 1000 m above sea level.
  • Permanent structure constructed from standard building materials (timber, masonry, concrete, metal, etc.)- and the roof material does not pose an excessive fire risk
  • In the case of existing Antenna on the roof, the top of the antenna is attached to the outside of the building, is less than 2.5 m above the gutter line and below the peak of the roof.

Note 2:

For any building that does not meet the above-mentioned conditions, a risk assessment for loss of life must be conducted.

5.1.2 Risk of Loss of Public Service

In the case of no requirement for installing exterior lightning protection system, To minimize the risk of damage to equipment inside the building, the risk of loss of service (R2) should be evaluated and compared to the tolerable risk of loss of service value RT2 = 10 –3 or a lower value according to the customer’s decision. Even when R1 < RT1, the customer should evaluate the  risk of loss of service R2 in accordance with [IEC 62305-2].

The Risk of loss of public Service is generally recommended for dwelling units meeting any of the following conditions.

  1. Supplied Directly by long length LV overhead line
  2. Supplied by a pole mounted MV/LV transformer in a way that shares a common earth electrode or has electrode systems located closely together.
  3. When there is a building with exterior lightning protection installed in the vicinity of the building.

5.2 Notes and Considerations Attributed to Risk Assessment.

5.2.1 PV Panel Considerations

When installing PV cells on a building’s roof, consider the following.

  • If the risk assessment indicates that the building requires exterior lightning protection at a level less than 3, PV panels should be protected according to Minimum Level 3, following the recommendations outlined in IEC TR 36227.
  • If the building is categorized as low risk, as specified in Clause 5.1.1.1, and exterior lightning protection is not required for the building stand alone, but regulatory conditions or insurance company requirements mandate lightning protection for PV panels, then the lightning protection system for PV cells should be installed compliance with Level 3.
  • In all cases, if the PV power circuit is not equipped with a Surge Protective Device (SPD), an exterior lightning protection system must be provided for the PV cells themselves.

5.2.2 Informative Notes

  • When it is determined that exterior lightning protection will be installed, Surge Protective Devices (SPD) needs be considered as part of the overall protection system.
  • When the decision is made not to install exterior lightning protection, it is essential to assess the calculated risk level (CRL) in accordance with standard I.S.10101. This evaluation helps determine whether the installation of Surge Protective Devices (SPD) is necessary. It’s important to note that transient overvoltage protection is exempt for single dwelling units if the total economic value of the electrical installation to be safeguarded is less than 5 times the economic value of the SPD situated at the origin of the installation.
  • In both small and large residential buildings, the risk of overvoltage and its consequences on the safety of individuals, whether individually or in groups, is generally minimal, unless there is an entry arial telecommunication line extended a long length outside the building. As a result, in the majority of cases, the protection measures resulting from a risk assessment primarily serve to safeguard electrical equipment. Therefore, property owners must decide whether to implement these measures, considering the economic aspects.
  • If an antenna is going to be installed on the roof, and the building is not required to have an exterior lightning protection system, the risk of antenna installation needs to be considered to avoid any potential increase in risk.
  • In a risk assessment, the density and arrangement of buildings need to be assessed by specialists if there is sufficient information available. See below for more information.

Building Congestion (Figure 1-1): This type of congestion assumes uniform building density within a 1 km2 area. It is mentioned to be typical in urban areas and cities where buildings are densely packed.

Different Building Arrangement Congestion (Figure 1-2): This congestion type represents a varied or different arrangement of buildings within a 1 km2 area. It is suggested to be applicable to suburban and rural areas where the building arrangement is less uniform compared to urban settings.

Note: In the case of a lack of information, the assumption shall be based on the same congestion configuration (Figure 1-1) as assumed in the sample calculation performed in IEC 62305

Different Building Arrangement congestion within 1km

Aerial shot of buildings.

Figure 1-1

Diagram of building layouts

Aerial view of buildings

Figure 1-2

 

Figure 1: Different Building Arrangement Congestion  within 1 Km 2

 

6. LPS Components

The general principles of installation for LPS components described in IEC 62305-3 shall be applied only when there is a necessity for structure protection against lightning. The important subjects that need emphasis in residential buildings are outlined below.

6.1 Material Selection

In general, the material and conditions of use shall be studied as guided in Table 5 of IEC 62305-3. The dimensions of the LPS components shall meet the minimum requirements stated in Tables 6 and 7 of IEC 62305-3, as well as the requirements from IEC 62561

Since the table allows the use of different metallic materials for LPS components, special consideration must be given to the joint connections of different materials and at transition locations between concrete and terrain/soil. The treatment to avoid a high rate of corrosion shall be taken into account, as stated in IEC 62305.

6.2 Air terminal System

The positioning of lightning rods shall adhere to the hypothetical sphere method as per IEC 62305. To achieve better efficiency of the air termination system, in cases where an exterior lightning protection system compatible with class IV is deemed necessary, it is recommended that the system be designed according to level III.

6.3 Down conductor

  • In the case of using reinforced rebars as a down conductor, appropriate bonding needs to be considered along the length of the column to ensure the best continuity. Moreover, if prefabricated reinforced concrete is used, a specialist needs to develop an appropriate detail illustrating the way of establishing interconnection points between the reinforcing elements. This detail should also show the conductive connection between the interconnection points.
  • In the case of pre-stressed concrete, attention should be paid to the risk of causing unacceptable mechanical consequences, due either to lightning current or as a result of the connection to the lightning protection system.
  • In all cases any part of down conductor which may be in accessible by ordinary people, the adequate protection shall be considered. Refer to figure 2. for further information.
    refer to clause 8 of IEC62305-3
  • As much as practicable, the separation distance needs to be maintained between the Lightning Protection System (LPS) and electrical/mechanical equipment to obviate the necessity of a bonding connection to the metal enclosure or structure. If a connection is necessary, the risk of the propagation of the surge inside the internal circuit needs to be investigated. Figure 3 illustrates the concept of maintaining the separation distance.
example of protective measures against contact voltages

Figure 2

Presentation on maintaining separation distance

Figure 3: Presentation on maintaining separation distance

6.4 Earth Electrode System

  • The purpose of the earthing system is to dissipate as much as possible the lightning current into the soil (50%) without producing dangerous potential differences in the earthing system. The earthing electrode system can also play a role in distributing the lightning current evenly through the down conductors.
  • When either Type A or Type B is used as an earth electrode system, the minimum length of the electrode shall meet the requirements specified in Clause 5.4.2 of IEC 62305-2. In this scenario, achieving an overall resistance for the electrode system lower than 10 Ohms is not obligatory but is recommended.
  • For buildings taller than 15 meters, Type B is highly recommended. In such cases, it can be established either by a counterpoised earthing system or by a foundation electrode system
  • When a foundation electrode system is used, the overall resistance shall be maintained below 10 Ohms.
  • In all cases, the bonding practice shall be such that it avoids any sparks through the concrete. For instance, if the discharge point of the lightning is within 3 meters of the pad foundation, the rebars inside the pad foundation should be connected to the earth electrode through which the lightning current is discharged to the soil.
  • It is recommended to always include vertical earth rods as part of the electrode system to enhance its efficiency.
  • Aluminum shall not b used in soil or in concrete.
  • An appropriate insulation shall be installed.at the transition location between concrete and terrain/Soil
  • If the discharge points of the lightning current are in areas with a high presence of people, it is recommended to consider additional rectification for the earth electrode system, as shown in Figure 4. Another solution in this scenario is the use of an insulation layer, as depicted in Figure 1. for further information refer to clause 8 of IEC62305-3.
Diagram showing example of potential control through a mesh grounding system

Figure 4

7. Test And Inspection

In general, all requirements need to align with what is stated in Section E.7 of IEC 62305-3. The following outlines the main and important items of the test and inspection.

7.1 Tests and Inspections During Construction

In General Those parts of the lightning protection system that will not be accessible at a later time (e.g. connections of the meshing, the terminal points, the anchor plates and the foundation earth electrodes as well as the connections to the reinforcement steel rods) shall be inspected before concreting or refilling to verify that they conform with the design reviewed construction documents. This is Applicable for Foundation earth electrode system.

7.2 Tests and Inspections after Assembly

  • The accessible parts of the Exterior Lightning Protection system shall be visually inspected with respect to fabrication quality and to the required dimensions, spacing and materials.
  • The conductive resistances via the ground ring, the down conductors and the connections shall be determined. The requirement of a maximum overall resistance of 0,2 Ω can be checked by measuring the resistance between the air-termination system and a ground plate at ground level.

7.3 Durable Tests and Inspections

The inspection frequencies given in Table 2 should apply where no specific requirements are identified by the authority having jurisdiction.

Table depicting maximum period between inspections of an LPS

Table 2

8. Early Streamer Emission Air Terminal Lightning Protection System

  • ESE air terminals are designed to generate upward streamers that launch sooner than conventional lightning rods, thus providing a more attractive point of termination. The applicable Standard for ESE system application is NFC17-102. Installation requirements and specific information about the protected zone is available from the systems’ manufacturers.
    The ESE System is Accepted to be used if all following conditions are met:

 

  • All requirements stated in NFC 17-102 are met.
  • The separation distance is maintained between the Lightning Protection System (LPS) components and any other metal part located in their vicinity. In cases where the separation distance cannot be maintained, the use of high voltage cable as a down conductor, as specified in (IEC62561-8), is preferred. Another approach to achieve a reduced separation distance is by increasing the number of down conductors.
  • In cases where the number of down conductors is limited, and consequently, a substantial amount of lightning current passes through a single down conductor, it is highly recommended to terminate the down conductors in areas with minimal human presence. This is done to mitigate any hazards associated with potential step voltage in that area. Additionally, the earth electrode system at the termination point of the down conductor should be designed to minimize step potentials as much as possible.
  • Each early streamer needs to be equipped by an adequate monitoring system and counter.
  • Specialists need to inform the client about any restrictions related to the installation of Early Streamer Emission (ESE) devices, including design life limitations, environmental use restrictions, and any other relevant considerations. Additionally, specialists should seek the approval of the client to use this system on the owner’s property. This ensures that the client is aware of and consents to the installation of the Early Streamer Emission (ESE) devices on their property.

9. Appendices

Appendix 1:

Calculation of risk assessment for the building categorized as a low risk building

Appendix 2:

Criteria for designing foundation earth electrode system.

Appendix 1

Generic risk assessment for Direct Strike

The following generic risk assessments have been according to [IEC 62305-2].

I.1 Input Data

Flashy Density :0.4 km2 /year
Ground floor area < 800 m
Height < 15 m.
Located on a hillside ≤ 1000 m.
Permanent structure from standard building materials.
The risk components related to a direct strike are RA and RB

Note A1: In the following context, RA and RB have been taken into account. Rc is only needed if human life is put at risk due to the failure of electronic equipment.

I.2 Calculation

R_1=R_A1+R_B1

R_A1=N_D×P_A×L_A
N_D=N_G×A_D×A_D×10^(-6)

N_G=0.4
A_D=12561 m^2
C_D=2 (Worst Scenario)

Therefore N_D=0.01

P_A=1(No Protection measures and no LPS)

L_A=r_t×L_T×n_A/n_t ×t_z/8760

r_t=10^(-2) (linoleum or wooden floors)
L_T=10^(-2) (Table C.2 of [IEC 62305-2])
n_z=1
n_t=1
t_z=8760

L_A=10^(-4)

Therefore R_A1=1 ×10^(-6)

R_B1=N_D×P_B×L_B

Now N_D=0.01

P_B=1(no LPS)

L_B=r_p×r_f×h_z×L_f× n_A/n_t ×t_z/8760

r_P=1(No provisions)
r_f=0.01(Ordinary)
h_z=1( No Special hazard)
L_F=10^(-2) (Table C.2 of [IEC 62305-2])
n_z=1
n_t=1
t_z=8760

Therefore L_B=10^(-4)

Therefore R_B1=1 ×10^(-6)

Direct strike risk to structure R1 = 2×10^(-6) (components RA1 + RB1 only).

Appendix 2: Criteria for Designing Foundation Earth Electrode

Diagram Showing the criteria for designing foundation earth electrode

Speak to Our Technical Team

Are you a architect, developer, or main contractor that builds residential properties in Ireland? Speak with our Technical Engineering team to discuss risk assessment for your projects!