Lightning Protection System – What it is?

Lightning Protection System - What it is?

Created by: Glen Zhu | Updated Date: May 6th, 2024

What is a lightning protection system?

A lightning protection system is designed to protect a structure, equipment, or people from the damaging effects of lightning strikes.

In a lightning protection system, electrical components are safeguarded by surge protective devices to stop surge while buildings or structures are protected with the help of external lightning protection, which comes in the form of lightning rods, metal conductors and earthing terminals.

Air-termination system: Provide a low-resistance path for lightning current to flow into the ground which includes lightning rods, air terminals, and conductors

Down conductors: Carry the lightning current from the air-termination system to the earthing system and offer a low-resistance path for the current

Earthing system: Dissipate the lightning current safely into the ground

Surge protective devices (SPDs): Protect sensitive electronic equipment from transient over-voltages caused by lightning

Equipotential bonding: Prevent dangerous potential differences during a lightning strike by ensuring all conductive parts within the structure are at the same potential

Figure 1 – A comprehensive lightning protection system

The purpose of a lightning protection system is to prevent property damage, fire, and personal injury from both the direct effects of a lightning strike and the secondary effects like electrical surges. By providing a low-impedance path to ground, the system directs the lightning current away from the structure and its contents, minimizing the risk of damage.

Lightning protection systems are essential for buildings, structures, and installations where the risk of lightning strikes is significant, such as tall buildings, power plants, telecommunication towers, and industrial facilities. They help safeguard against the fire hazard and structural damage that can result from lightning strikes.

Lightning protection system design

How to install a lightning protection system? Before we take measures to protect our property from lightning strikes, risk assessment is a must to evaluate the risk and take decisions on limiting these unexpected risks.

The Class of LPS

Risk management includes determination of lightning protection level, selection of lightning protection method and calculation of lightning protection system design.

The class of LPS is stated in IEC standards, which classifies the lightning protection system into four classes based on their intended level of protection. The purpose of having different LPS classes is to determine the maximum lightning current parameters that the LPS must to be handle.

The sources of damage, types of damage and types of loss are specified.

Class I: This provides the primary level of lightning protection, typically used for direct lightning strikes to a structure which may cause loss of human life. Requires the smallest rolling sphere radius in the design.

Class II: This level refers to damage from lightning strike near a structure that may cause loss of service to the public.

Class III: Focus on direct lightning strike to an incoming line and loss of cultural heritage.

Class IV: This is the lowest level of the protection, damage is caused by lightning strike near an incoming line. Economic value is the possible loss.

Point of strike Example Type of damage Type of loss
Structure S1

D1

D2

D3

L1, L4b

L1, L2, L3, L4

L1a, L2, L4

Near structure

S2

D3 L1a, L2, L4

Incoming line

S3

D1

D2

D3

L1, L4b

L1, L2, L3, L4

L1a, L2, L4

Near incoming line

S4

D3 L1a, L2, L4

a  For hospitals and other structures where failures of internal systems immediately endangers human life and structures with a risk of explosion.

b  For agricultural properties (loss of animals)

Lightning protection zone

Figure 2 – Lightning protection zone concept

The building or structure is divided into different lightning protection zones with varying level of protection against the direct effect of lightning strikes and the associated electromagnetic fields.

LPZ 0A: Unprotected zone exposed to direct lightning strikes and full electromagnetic fields.

LPZ 0B: Protected against direct strikes but still exposed to full electromagnetic fields.

LPZ 1: Zone where surge currents are limited by current distribution and surge protective devices.

LPZ 2 and higher: Zones where surge currents are further limited by additional SPDs and shielding.

The transition between zones, such as from LPZ 0B to LPZ 1, requires the installation of appropriate SPDs to protect against the surge currents and electromagnetic fields.

External lightning protection

Air termination system

It serves as the fundamental element of an external lightning protection system. The purpose of the air termination system is to intercept and capture the lightning strike, and then safely channel the lightning current to the down conductors and earth.

There are three different methods used to design the air termination system:

Mesh method: The mesh could be placed on roof edges, overhangs and ridge lines as the metal natural part of the building serving as an air-termination system, regardless of the height of the structure and shape of the roof.

Protection angle method: This method must be used for buildings with symmetrical dimensions, where the areas of protection and unprotection must be equal or roof-mounted structures like antennas, domelights.

Rolling sphere method: The most universal method that can be applied to all types of structures.

Figure 3 – Method for designing of air-termination systems

The rolling sphere method involves rolling a sphere of a certain radius (determined by the lightning protection level) over the structure. Air terminals are placed at all points where the sphere touches the structure.

The radius of the rolling sphere varies based on the class of lightning protection system, with smaller radii corresponding to higher levels of protection. For example, Class I has the smallest radius of 20m, while Class IV has the largest radius of 60m.

The rolling sphere method takes into account the possibility of side strikes, where lightning can strike the side of a tall building above the rolling sphere’s radius. However, the probability of such side strikes is considered negligible for structures less than 60m in height.

Calculations can be performed to determine the separation distance between air terminals and the penetration depth of the rolling sphere between two air terminals.

Air termination products like air rods, raised conductors, and mesh are specifically designed to provide effective protection against direct lightning strikes.

Isolated and non-isolated air-termination systems

When we design the external lightning protection system of a structure, we have to types of air-termination systems: isolated and Non-isolated. Or when should we combine these two?

Non-isolated air-termination system is recommended to install on the gable or flat roofs which are made of non-flammable materials. Small air terminals and roof mesh conductors directly connected to the building, are suitable for simpler structures or roof-mounted equipment like small fans.

Isolated air-termination system uses insulated conductors and supports to maintain a separation distance between the lightning protection system and any conductive parts of the building. They are frequently used for the roofs covered with flammable materials or systems located in hazardous areas.

Metal structural parts such as attics, guttering, railings, and cladding, can be used as natural components of air-termination system. It is noted that they must comply with the minimum dimensions specified.

Class of LPS Material Thicknessa t[mm] Thicknessb t’[mm]
I to IV Lead 2.0
Steel(stainless,galvanised) 4 0.5
Titanium 4 0.5
Copper 5 0.5
Aluminium 7 0.65
Zinc 0.7
at prevents puncture
bt only for sheet metal if puncture, overheating and ignition does not have to be prevented

Down conductors

The electrically conductive connection between the air-termination system and the earth-termination system is the down conductor system. The function of down-conductor systems is to safely transport intercepted lightning current to the earth-termination system without causing excessive temperature spikes that could harm the structure.

It must be mounted to ensure that the system is unharmed during the lightning current discharge. Multiple parallel currents run to create connections for conductive components of the structure. These currents can be straight, vertical and with no loops.

The numbers of down conductors and distances between conductors depend on the lightning protection system class. The higher protection classes are, the more down conductors needed.

The IEC 62305-3 standard specifies typical distances between down conductors for each lightning protection class, ranging from 10m for Class I to 20m for Class IV.

Class of LPS

Typical distance

I

10m

II

10m

III

15m

IV

20m

Down conductors can be made of aluminum, copper, or stainless steel, with minimum cross-sectional areas specified based on the protection class.

Structural elements like metal facades, frames, and reinforcements can be used as natural down conductors if they meet the minimum size and interconnection requirements.

Material

Configuration

Cross-sectional

area in [mm2]

Copper,

Tin-plated copper

Solid tape

50

Solid roundb)

50

Strandedb)

50

Solid roundc)

176

Aluminium

Solid tape

70

Solid round

50

Stranded

50

Down conductors should be positioned along the perimeter of the structure, especially near corners, and connected to the earth termination system at regular intervals (every 20m vertically).

For structures with rooftop equipment, an “isolated” down conductor system may be used to prevent lightning currents from entering the building.

Earthing termination

The purpose of the earth termination system is to provide a low-impedance path to dissipate the lightning current safely into the ground.

The earth termination system should be designed to have a resistance to earth of less than 10 ohms, as per the IEC/BS EN 62305 standards.

Common earth electrode arrangements include:

Type A: Horizontal star-type earth electrodes or vertical earth electrodes installed outside the structure

Type B: Ring earth electrodes installed around the perimeter of the structure

Figure 4 – Ring earth electrode around a residential building

The minimum total length of earth electrodes required at each down conductor location is calculated based on the soil resistivity and lightning protection class.

For a Class I lightning protection system in 2000 ohm-m soil, the minimum total length of earth electrodes per down conductor could be 50 meters of horizontal conductors or 25 meters of vertical electrodes.

If using driven earth rods, a minimum length of 1.5 meters per rod is recommended, with the total combined length of all rods being at least 9 meters.

Parallel earth rods should be spaced at a distance at least equal to their driven depth, or a “crow’s foot” configuration can be used.

Bonding of all metallic structures and services to the earth termination system is crucial to prevent side-flashing and potential differences.

The earth termination system should be integrated with the main electrical earthing system of the building for effective lightning protection.

Internal lightning protection

Equipotential bonding

Modern buildings, with their extensive metallic piping and electrical systems, can provide internal paths for lightning, increasing the risk of damage and danger to people. Lightning strikes can generate voltage spikes of up to 1,000,000 volts, with the potential for side flashes or arcing over alternate ground paths, posing serious fire and explosion hazards.

A comprehensive lightning protection system addresses this issue through equipotential bonding – the interconnection of all metallic building systems with the lightning protection grounding system. When all grounded systems are bonded together, it creates a common ground potential, ensuring the lightning current follows the intended path to ground rather than taking alternative routes.

This equipotential bonding is required to interconnect every grounded building system and continuous metallic piping with the lightning protection grounding electrode system near ground level. For low-profile structures, interconnection near the roof may be sufficient if the components are in close proximity. However, taller buildings require interconnection of the internal grounded systems at the roof, ground, and intermediate levels to maintain potential equalization and prevent arcing.

Figure 5 – Lightning equipotential bonding

Incorporating the building’s steel superstructure into the lightning protection system helps maximize the splitting of the lightning current, further minimizing potential differences internally. Standards also require bonding the lightning protection downleads to the reinforced concrete columns at both the top and bottom.

The bonding of grounded systems is typically done with smaller fittings and cables, though in some cases, using full-size system components may be easier when they are located near the desired bonding points. When bonding within the construction or below grade, larger components are often used for greater mechanical strength against construction realities.

In summary, the extension of the lightning protection system to include comprehensive equipotential bonding of all grounded systems is a critical element in the overall design, ensuring the safety and integrity of the building and its people.

Surge protection

External lightning protection system are designed to protect against direct lightning strikes on buildings from being burning down as the first step protection. The installation of surge protective devices is to deal with indirect strikes, providing protection on circuits associated with electrical, communication, and/or data lines that transmit lightning into a structure.

While lightning is the most significant source of electrical surges, it only accounts for about 20% of all transient events. The remaining 80% of surges are generated internally within the facility, originating from equipment like motors, HVAC systems, and office electronics.

To fully protect the internal electrical systems and sensitive equipment, surge protective devices are required. SPDs work by transitioning from a high-impedance state to a low-impedance state when a surge event occurs, diverting the surge current away from the protected equipment. This limits the instantaneous overvoltage that can penetrate the power lines and damage connected systems.

Electrical safety standards, such as IEC 62305, specifically mandate the use of SPDs in conjunction with a lightning protection system. This ensures the voltage and current entering the building are effectively limited, preventing damage to sensitive electronic equipment.

There are different types of surge protective devices on the market. The most common classification is the AC or DC surge protective devices, respectively working for AC and DC power systems. Type class is also a way to choose your suitable surge protective devices.

Click and get to know more about surge protective devices.

Inspection and maintenance

Regular inspections are essential to ensure the lightning protection system remains effective and compliant with safety standards. It is recommended to conduct visual inspections at least annually, and more comprehensive inspections every 3-5 years, or whenever structural changes are made to the building.

IEC 62305-3 requires the inspection of a lightning protection system based on class of LPS .

Class of LPS Visual inspection (year) Complete Inspection (year) Complete inspection of critical situtionsa)b) (year)
I and II 1 2 1
III and IV 2 4 1
a)  Lightning protection systems utilised in applications involving structures with a risk caused by explosive materials should be visually inspected every 6 months. Electrical testing of the installation should be performed once a year. An acceptable exception to the yearly test schedule would be to perform the tests on a 14 to 15 month cycle where it is considered beneficial to conduct earth resistance testing over different times of the year to get an indication of seasonal variations.
b)  Critical situations could include structures containing sensitive internal systems, office blocks, commercial buildings or places where a high number of people may be present.

The visual inspections should check for:

  • Loose connections
  • Corrosion or damage to components
  • Secure attachment of conductors and components
  • Compliance with the current or other relevant standards

Comprehensive inspections should also include:

  • Site assessment to identify vulnerable areas
  • Risk assessment to determine the appropriate level of protection
  • Continuity and resistance testing of the grounding system
  • Testing of surge protection devices

Inspection and maintenance records should be maintained, as they can be crucial during audits or inspections by regulatory bodies.

Facilities with a higher risk of lightning strikes, such as those in areas with high lightning activity or those with critical equipment, may require more frequent inspections (e.g. every 6 months).

The use of specialized equipment, such as lightning event counters, can help monitor the system’s performance and trigger inspections after significant lightning activity.

Prompt repair of any identified deficiencies is essential to ensure the lightning protection system continues to provide the necessary level of protection.

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