Electrical Notes & Articles

Basic of External Lightning Protection System (LPS)-(Part-4)

Material Combinations and Dimensions

• Required to use galvanically compatible metals in lightning protection system components and surface materials on which the components are mounted. For example, do not connect copper to aluminum.
• Do not use together metals that are not galvanically compatible. Bad matching accelerates their corrosion in the presence of moisture.
• With aluminum conductors, use only connection devices designed for aluminum. Make sure to use the right fastening torque.

LPS Material

Material Dimensions

• Several lightning protection system codes and standards define minimum dimensions for the components of a grounding system. These standards are designed to protect buildings and other inhabited or otherwise critical facilities.
• Practical minimums are based on field experience and indicate what is needed to protect the installed equipment in a cost-effective way during the foreseeable technical lifetime, typically a few decades, taking into account local regulations. To ensure proper operation of the grounding system, periodic inspection and maintenance is needed

Minimum Dimensions of Earth Electrode as per IEC 623053 

• Table 1 and Table 2 are based on standard IEC 62305-3 Ed 2. The tables list minimum dimensions for the lightning protection system equipment.
• The following table lists the different materials and shapes that are used in air terminals, down conductors, and ground electrodes, including the cross-sectional area.

Minimum Cross-sectional Area of Air-termination Conductors

Minimum values of the cross-section of the bonding conductors with different bonding bars

Minimum Dimensions

Guideline for LPS System:

• The following design guidelines need to be adhered to ensure safer installation of the external LPS.
• Air Terminal:
• Air terminal should be selected and provided only based on the protection angle or rolling sphere method
• Proper safety distance between the air terminal and any metallic object needs to be maintained as per the calculation mentioned earlier to avoid dangerous spark-overs.
• Different Material Jointing & Insulations:
• Wherever incompatible materials to be joined (Ex. Copper with Aluminum), suitable bi-metal connectors should be used.
• Suitable expansion joints must be provided on the horizontal conductors on top to take care of thermal effects.
• Special conductor holders of insulating type need to be provided on top of the terrace floor for routing the conductor to ensure electrocution impact does not happen in case of water stagnation.
• Equip potential Bonding:
• Required measures to ensure shielding, bonding / equipotential bonding techniques are handled properly to avoid LEMPs.
• Establishing connection for equipotential bonding with nearby metallic components need to be taken care of.
• Joints should be mechanically and electrically effective, should be protected against corrosion or erosion from the elements or the environment and should present an adequate contact area.
• Reinforcement Structure:
• In the case of using reinforcement in concrete structures as lightning down conductor details should be decided at the design stage, before building construction begins.
• Good contact between reinforcing bars to be ensured only by using connection clamps tested as per the requirement of IEC 62561-1
• Down Conductor:
• A down-conductor should be installed at each exposed corner of the structure where it is possible.
• The Down conductor should run as straight and vertical as possible so that they provide the shortest and most direct path of a low impedance from the air termination to the earth electrode so that the lightning current can be safely conducted to earth.
• The formation of loops in bring the down conductor shall be avoided, but where this is not possible the distance shall be maintained
• There should be a test joint arrangement to have separation between down conductor and earth termination for safety and for measurement of earth resistance.
• At least two down conductors are mandatory for any size of Building.
• The termination of the down conductor to an earth electrode should be done minimum of 1 meter away from the structure and minimum of 0.5m depth inside the ground.
• Earth electrodes for each down conductor shall be provided.
• Connection of down conductors to gutters or down-spouts even if they are covered by insulating materials.
• Usage of multiple connections with different materials should not be permitted.
• Insufficient conductor dimensions (non-complying material as mentioned in IEC 62305-3 Table – 5) should be strictly avoided.
• When the distance from down conductors to combustible materials cannot be assured, the cross section of the down conductor shall not be less than 100 mm²

Basic of External Lightning Protection System (LPS)-(Part-3)

COMPARISION OF VARIOUS PROTECTION METHOD

(2) Down Conductor system:

• In Air-termination systems, down-conductor systems and earth-termination systems should be harmonized to produce the shortest possible path for the lightning current.
• Down-conductors should preferably be connected to junctions of the air-termination system network and routed vertically to the junctions of the earth-termination system network.
• The function of a down conductor system is to conduct the lightning impulse from air-termination system to the earthing system. The down conductor system should be installed in such a way that the following points are ensured.
• (i) Several parallel current paths exist
• (ii) Length of current path is kept to minimum.
• (iii) Equipotential bonding to conducting parts is performed.
• Selection and installation of down conductors plays a major role in protecting electrical and electronic installations in a building. The number of down conductors to a typical building depends upon the class of LPS.
• A down conductor should be installed at each exposed corner of the structure and form a direct continuation of the air-termination conductors. Drown conductors are installed in such a way that they provide the shortest and most direct route to earth. Avoiding the formation of bends and loops is required.
• To reduce damage caused by lightning current, the down conductors are arranged so that the current path around the building’s perimeter is parallel and at equal distances.
• Even if the down conductor encased in insulating material, down conductors must not be installed in service shafts, gutters, or downspouts, as doing so invites severe damage during a lightning strike.
• Electrical insulation between LPS components and other metallic installation in the building are necessary to avoid flashover between different metal parts.
• Integration of down conductor with Building Natural Components:
• External down-conductors should be installed between the air-termination system and the earth-termination system. Wherever natural components (Steel reinforcement, metal framework structure) are available, they can be used as down-conductors.
• Down conductors are also integrated into structural steel reinforcement, metal framework of structure, steel roof, metal façade, handrails etc. is the best and practical solution for new and upcoming high raise buildings. In this integrated approach high safety is offered with no maintenance, long life, no influence on aesthetics. Separation distance need not be considered in this case.
• Down conductors can be embedded in RCC columns. In this case, bonding different metallic installations in the building is simple, thereby eliminating potential differences. This integrated method is not only cost-effective but has no negative effect on the building’s aesthetics. It also reduces the failure of electronic equipment inside the building from radiated lightning effects.
• Test joints are not required, and earth resistance measurements are not necessary in the location where the natural down conductors are terminated to foundation earthing.

• Number & distance between each Down Conductor:
• For each non-isolated LPS, the number of down conductors shall be not less than two and should be distributed around the perimeter of the structure to be protected. An equal spacing of the down conductors is preferred around the perimeter. The typical values of the distance between the conductors are shown below.

• If the distance between down-conductors is too large with the reference to the Table, the number of down-conductors should be increased to meet the required separation distance.
• As stated, a down-conductor should be installed at each exposed corner of the structure, where this is possible. However, an exposed each corner does not need a down conductor if the distance between this exposed corner to the nearest down-conductors complies with the following conditions:
• (i)the distance to both adjacent down-conductors is half the distance according to Tables or smaller.
• (ii) the distance to one adjacent down-conductor is one-quarter of the distance according to Tables or smaller.

• The number and position of down-conductors is important because if the lightning current is shared in several down-conductors, the risk of side flash and electromagnetic disturbances inside the structure is reduced. It follows that, as far as possible, the down-conductors should be uniformly placed along the perimeter of the structure and with a symmetrical configuration.
• The current sharing is improved not only by increasing the number of down-conductors but also by equipotential interconnecting rings.
• Down-conductors should be placed as far as possible away from internal circuits and metallic parts in order to avoid the need for equipotential bonding with the LPS., In cantilevered structures the separation distance should also be evaluated with reference to the risk of side-flashing to persons.
• If it is not possible to place down-conductors at a side, or part of a side, of the building because of practical or architectural constraints, the down-conductors that ought to be on that side should be placed as extra compensating down-conductors at the other sides. The distances between these down-conductors should not be less than one-third of the distances in Table.
• A variation in spacing of the down-conductors of ±20 % is acceptable as long as the mean spacing conforms to Table.
• In closed courtyards with more than 30-meter perimeter, down-conductors have to be installed.
• Insulation / Separation of LPS parts
• If it is not possible to make a straight connection because of large roof overhangs, etc. the connection of the air-termination system and the down-conductor should be a dedicated one and not through natural components like rain gutters, etc.
• It is permitted, where aesthetic consideration needs to be taken into account, to use a thin coating of protective paint or PVC covering over the external down-conductors.
• Down conductors, even if covered in insulating material, shall not be installed in gutters or waterspouts. The effects of moisture in the gutters lead to intensive corrosion of the down conductor.

• For non-isolated LPS, down conductors are mounted directly onto the building (without separation distance) if the wall is made of flame resistant or normally inflammable material, the down conductors may be installed directly on or in the wall.
• Metal framework of a steel structure or the interconnected reinforcing steel of the structure can be used as a down conductor. Reinforcement of existing structure cannot be used as natural down conductor unless the reinforcement is safely interconnected. Separate external down conductors must be installed.
• Conductors on roofs and the connections of air-termination rods may be fixed to the roof using both conductive or non-conductive spacers and fixtures. The conductors may also be positioned on the surface of a wall if the wall is made of non-combustible material.
• Recommended fixing centers for these conductors are shown in the Table.

(3) Earth Termination:

• The purpose of the earth termination system is to provide a safe low-impedance path to high frequency lightning current into the ground.
• To minimize dangerous over voltage due to lightning, The shape and the dimension of the earth termination system are important.
• 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.
• There are two basic types of earth electrode arrangements are recommended in IS/IEC 62305 and NBC-2016 such as vertical /horizontal
• Type A arrangement: Horizontal earth electrodes or vertical earth electrodes installed outside the structure and connected to down conductors.
• Type B arrangement: Ring earth electrodes installed around the perimeter of the structure.
• POINTS NEED TO BE CONSIDER:
• Step Voltage: If earthing termination network is used in public access area, then the selection of suitable types of earth electrodes and safe distances from structure and from the external conductive parts in the soil (cables, metal ducts, etc.) are important. Hence special steps need to be taken for the protection against dangerous step voltages in the vicinity of the earth-termination networks.
• Earth resistance value: The recommended value of the overall earth resistance of 10 Ω is fairly conservative in the case of structures in which direct equipotential bonding is applied. The resistance value should be as low as possible in every case but especially in the case of structures endangered by explosive material. Still the most important measure is equipotential bonding.
• Depth of Electrode: The embedded depth and the type of earth electrodes should be such as to minimize the effects of corrosion, soil drying and freezing and thereby stabilize the equivalent earth resistance.
• It is recommended that the first half meter of a vertical earth electrode should not be regarded as being effective under frost conditions. Deep-driven earth electrodes can be effective in special cases where soil resistivity decreases with depth and where substrata of low resistivity occur at depths greater than those to which rod electrodes are normally driven.
• Mechanical Splitting / Stressing: When the metallic reinforcement of concrete is used as an earth electrode, special care should be exercised at the interconnections to prevent mechanical splitting of the concrete.
• If the metal reinforcement is also used for the protective earth, the most severe measure in respect of thickness of the rods and the connection should be chosen. In this case, larger sizes of reinforcement bars could be considered. The need for short and straight connections for the lightning protection earthing should be always recognized.
• In the case of pre-stressed concrete, consideration should be given to the consequences of the passage of lightning discharge currents, which may produce unacceptable mechanical stresses.

(A) Type-A Earthing (Embedded Earth Electrode)

• This is the conventional type of LPS Earthing System where earthing rodsare used to form the earth electrode and connected each down conductor to an earth rod. The earth electrodes installed outside the structure.
• The type A earth-termination system is suitable for low structures (family houses ,Low rise building).
• This type of arrangement comprises horizontal or vertical earth electrodes connected to each down-conductor.
• Where there is a ring conductor, which interconnects the down-conductors, in contact with the soil, the earth electrode arrangement is still classified as type A, if the ring conductor is in contact with the soil for less than 80 % of its length.
• The total number of earth electrodes in Type A arrangement shall not be less than two.
• Type-A earthing suitable for:
• The type A earth termination arrangement is suitable for low structures (Houses), (below 20 meters in height)
• existing structures or an LPS with rods or stretched wires or for an isolated LPS.
• It is suitable for locations with low fault currents and provides safety and functional grounding.
• commonly used in residential and commercial settings.
• Type A earthing system depends upon the soil resistivity and class of LPS.
• Each down conductor shall have a vertical earth electrode with a minimum length as per the table. In case of horizontal electrode, the length shall be double.
• The earth electrodes shall be installed at a depth of upper end at least 0.5 m in soil if an earth chamber is not used.
• In general, a low earthing resistance (if possible lower than 10 Ω when measured at low frequency) is recommended for type A earthing if the specific length cannot be ensured.
• The minimum length of each earth electrode at the base of each down-conductor is specified in BS EN 62305 and the table below.

• The minimum length of each earth electrode at the base of each down-conductor is l1 for horizontal electrodes, or 0.5 x l1 for vertical (or inclined) electrodes,
• where l1 is the minimum length of horizontal electrodes. For combined (vertical or horizontal) electrodes, the total length shall be considered.
• Reduction of earthing resistance by the extension of earth electrodes is practically convenient up to
• 60 m. In soil with resistivity higher than 3000 Ωm, the use of type B earth electrodes or earthing enhancing compounds is recommended.

• Radial and vertical earth electrodes
• Each down-conductor should be provided with an earth electrode.
• Radial earth electrodes should be connected to the lower ends of the down-conductors by using test joints.
• During installation it is necessary to measure the earthing resistance regularly. Additional electrodes can then be installed in more suitable locations.
• The earth electrode should have sufficient separation from existing cables and metal pipes in the earth. The separation distance depends on the electrical impulse strength and resistivity of the soil and the current in the electrode.
• In the type A arrangement, vertical earth electrodes are more cost-effective and give more stable earthing resistances in most soils than horizontal electrodes.
• In some cases, it may be necessary to install the earth electrodes inside the structure, for example in a basement or cellar.
• Advantages:
• If there is a danger of an increase in resistance near to the surface, it is often necessary to employ deep-driven earth electrodes of greater length. Radial earth electrodes should be installed at a depth of 0,5 m or deeper. A deeper electrode ensures that in countries in which low temperatures occur during the winter, the earth electrode is not situated in frozen soil (which exhibits extremely low conductivity).
• An additional benefit is that deeper earth electrodes give a reduction of the potential differences at the earth surface and thus lower step voltages reducing the danger to living creatures on the earth surface. Vertical electrodes are preferred to achieve a seasonally stable earthing resistance.
• Limitation:
• When the type A earthing arrangement is provided, it is necessary to all electrodes are at equal equalization. This can be achieved by bonding all conductors by bonding bars. Special care also needs to be cared to control step voltage.

(B) Type-B Earthing (Foundation /Ring Earthing)

• Type B Earthing consists of either a Ring conductor external to the structure to be protected (in contact with the soil for at least 80% of its total length) or a Foundation earth electrode forming closed loop.
• Type-B Earthing is also done by combination of both Ring earthing and Foundation earthing.
• Foundation earthing is done using conductors embedded in foundation of the building.
• Foundation earthing also serves as protective and functional earthing. This is the most efficient earthing system to protect electronic equipment. Materials used and construction techniques availed must fulfil various mechanical, electrical and chemical requirements to provide long life for the installation.
• Connection of a Lightning Protection System to the steel in the concrete foundation can be done for all new constructions since this steel is usually good for equipotential bonding. A dedicated Earth Rod can also be installed in the foundation but then these Earth Electrodes would need to be bonded to the steel in the concrete.
• Earth-termination systems should serve the following three purposes.

1. conduction of the lightning current into the earth.
2. equipotential bonding between the down-conductors.
3. potential control in the vicinity of conductive building walls.

• The foundation earth electrodes and the type B ring-type earth electrodes meet all these requirements.
• Type A radial earth electrodes or deep-driven vertical earth electrodes do not meet these requirements with respect to equipotential bonding and potential control.
• The structure foundations of interconnected steel-reinforced concrete should be used as foundation earth electrodes. They exhibit very low earthing resistance and perform an excellent equipotentialization reference. When this is not possible, an earth-termination system, preferably a type B ring earth electrode, should be installed around the structure.
• Type-B Earthing Suitable for:
• Structures built on rocky ground
• Structures housing sensitive electronics/equipment
• Large structures
• It is used in areas with high fault currents, such as critical infrastructure and industrial facilities, to provide enhanced protection against surges and transients, often resulting from lightning or equipment malfunctions.
• The type B earth-termination system is preferred for meshed air-termination systems and for LPS with several down-conductors.
• Type B is recommended for buildings with electrical and electronic installations and buildings in high soil resistivity.
• Type B earth electrodes also perform the function of potential equalization between the down conductors at ground level, since the various down-conductors give different potentials due to the unequal distribution of lightning currents due to variations in the earth resistance and different lengths in the above ground conductor current paths. The different potentials result in a flow of equalizing currents through the ring earth electrode, so that the maximum rise in potential is reduced and the equipotential bonding systems connected to it within the structure are brought to approximately the same potential.
• In some Area it is not possible to install a ring earth electrode that will fully surround the structure Where structures belonging to different owners are built closely to each other or common for both. In this case the efficiency of the earth-termination system is somewhat reduced, since the conductor ring acts partly as a type B electrode, partly as foundation earth and partly as an equipotential bonding conductor.
• Where large numbers of people frequently assemble in an area adjacent to the structure to be protected, further potential control for such areas should be provided. More ring earth electrodes should be installed at distances of approximately 3 m from the first and subsequent ring conductors. Ring electrodes further from the structure should be installed more deeply below the surface i.e. those at 4 m from the structure at a depth of 1 m, those at 7 m from the structure at a depth of 1,5 m and those at 10 m from the structure at a depth of 2 m. These ring earth electrodes should be connected to the first ring conductor by means of radial conductors.
• POINTS NEED TO BE CONSIDER:
• If it is not possible to close the ring, a connection must be made inside the buildingusing conductive metallic equipment such as pipes.
• Ring shall be at least 0.5meter below the surface
• Ring shall be maintained at least 1 meter from the structure / from the external walls.
• It is recommended that 80% of the length of the ring shall be in contact with natural soil. Thus, no more than 20% of the total length may be in the basement of the structure instead of in direct contact with the soil.
• If the radius of the ring electrode is less than the length of vertical or horizontal earth electrodes required for Earthing, then additional horizontal or vertical earth electrodes can be connected to the ring.
• Bonding of different metallic installations in the building avoid dangerous potential differences and flashover
• Ring earth electrode Radius length: For the ring earth electrode (or foundation earth electrode), the mean radius (re) of the area enclosed by the ring earth electrode (or foundation earth electrode) shall be not less than the horizontal electrodes value (l1)
• re ≥ l1
• When the required value of l1 is larger than the convenient value of re, additional horizontal or vertical (or inclined) electrodes shall be added with individual lengths lr (horizontal) and lv (vertical) given by the following equations:
• lr = l1 – re (2) and lv = (l1 – re) / 2
• It is recommended that the number of electrodes should be not less than the number of down-conductors, with a minimum of two.
• The additional electrodes should be connected to the ring earth electrode at points where the down-conductors are connected and, for as many as possible, equidistantly.
• EARTH TERMINATION SYSTEM IN LARGE AREAS:
• An industrial plant typically comprises a number of associated structures, between which a large number of power and signal cables are installed. The earth-termination systems of such structures are very important for the protection of the electrical system. A low impedance earth system reduces the potential difference between the structures and so reduces the interference injected into the electrical links.
• A low earth impedance can be achieved by providing the structure with foundation earth electrodes and additional type B and type A earth arrangements.
• Interconnections between the earth electrodes, the foundation earth electrodes and the down conductors should be installed at the test joints. Some of the test joints should also be connected to the equipotential bars of the internal LPS.
• Internal down-conductors, or internal structural parts used as down–conductors, should be connected to an earth electrode and the reinforcement steel of the floor to avoid step and touch voltages. If internal down-conductors are near expansion joints in the concrete, these joints should be bridged as near to the internal down-conductor as possible.
• The lower part of an exposed down-conductor should be insulated by PVC tubing with a thickness of at least 3 mm or with equivalent insulation.
• When the area adjacent to the structure is covered with a 50 mm thick slab of asphalt of low conductivity, sufficient protection is provided for people making use of the area.

• Foundation Earth Electrodes are simply concrete reinforced foundations – they are considered to be Type B Earthing. For these Foundation Earth Electrodes, there should be at 50mm of concrete covering the electrode to minimize corrosion.
• The type B earthing is recommended as either a ring conductor outside the perimeter of the structure which it’s recommended should be in contact with the soil for at least 80% of its total length.
• The alternative is to use a foundation earth electrode which can be in a mesh form.
• The reinforced concrete floor slab can be used around the structure.
• If the required resistance cannot be achieved by this method the vertical or radial earthing electrodes can be added to the network.
• For ease of testing after installation an inspection pit with an earth bar should be installed where the legs of the ring and conductor routing onto the ring from each test clamps join
• FOUNDATION EARTHING / NATURAL CONDUCTORS AS PART OF THE LPS
• The building’s natural components, metal roof, rebar, steelwork etc. can be considered as part of the LPS
• The reinforcing bars within the concrete structure can be used as a natural component of the LPS provided they are electrically continuous by either welding or clamping the joints.
• The re-bars are considered as electrically continuous provided that a major part of interconnections of vertical and horizontal bars are welded or otherwise securely connected by clamps conforming to BS EN 50164 standards.
• Forming:
• Foundation grounding is one of the most healthy grounding methods. Foundation grounding of buildings must be started at the beginning of construction, i.e. foundation stage. It is performed by installing a galvanized conductor between the reinforcing bars in the foundation. This conductor is connected to reinforcing bars at certain distances. The ends of the grounding conductor are taken out from some specified points and left as the connection bud. Once these ends are connected to the equipotential grounding bus bars, the grounding is completed by connecting all systems to be grounded to these buses.
• Foundation grounding must be performed in the form of a closed ring and placed in the foundation of the external walls of the building, or the foundation platform. In buildings with a large perimeter, foundation grounding rods must be divided into sections of 20x20m. Connection must be established with reinforcing bars every few meters.
• Foundation earthing can be accomplished in various ways, such as by using cable or flat conductor, connected to earth rods or by surrounding the foundation with conductor that enters the foundation through an earth terminal. Grounding standards, such as IEEE 80 Standard, provide guidelines for the design and installation of earthing systems, including those for foundations.
• For the foundation earthing’s connection with a lightning rod, a conductor is placed inside the pillars before the concrete placement, ending on the building’s rooftop.
• Circumferentially on the rooftop, an aluminum or copper conductor is placed on braces, in spots that include chimneys, solar water heaters, etc. Then spikes are placed, and the construction of the lightning rod is complete

• The connecting rebar must overlap and be clamped using rebar clamps or welded to a minimum of 20 times the diameter of the rebar a (Welding to be done on either side of the rebars.)
• The concrete used for the foundations of buildings has a certain conductivity (relative comparison) and, in general, “a large contact area” with the ground. It is highly recommended to use bare metal electrodes completely embedded in concrete (to a minimum depth of 5 cm) for grounding purposes, as they are highly protected against corrosion, usually for the entire life of the building according to IEC 60364
• It is recommended to use a foundation earth electrode embedded in concrete during the construction of the building (itself) to obtain a lower earth resistance value.
• Materials for Earth-Termination Systems
• The foundation earth electrode has to be made of
• Round steel (min. diameter 10 mm) or
• Strip steel (min. dimension 30 mm x 3.5 mm) which has to be galvanized (or black) for laying in concrete, or for laying in soil.
• Advantages:
• Does not require additional excavation work.
• Provides good contact with the ground.
• It extends over virtually the entire surface of the building foundation and results in minimum ground electrode impedance that can best be achieved with this surface.
• It also provides an optimal grounding arrangement for the lightning protection system.
• It is erected at a depth that is normally free from negative influences resulting from seasonal weather conditions.
• Step voltage elimination
• Equipotential connections
• Corrosion resistant

Basic of External Lightning Protection System (LPS)-(Part-2)

(B) ROLLING SPHERE METHOD: (Suitable for complex shape building)

•  The rolling sphere method should be used to protect the areas of a structure when there is design limitation to use the protection angle method.
• The rolling sphere method is recommended as the main method to be used in the design of lightning protection system with location of air terminals for structures with complex shapes.
• This method is more accurate, and complex compared to other lightning protection schemes, because it specifies the exact number of spikes needed for each building and considers the worst-case scenarios, in which a lightning strike hits the side of the building.
• Position of Air Termination Rod:
• In this method, the positioning of the Air-Termination system is adequate so that no point of the structure to be protected comes in to contact with a sphere with radius ‘r’ depending on the class of LPS (see table) rolling around on top of the structure in all possible directions. In this way, the sphere only touches the air termination system (see figure).
• Radius of Sphere:
• The rolling sphere lightning protection method assumes the electrically charged field that produces a lightning strike has a radius “r” and the sphere with that radius rolling over the surface of the building. Any place the sphere touches the building is a location where lightning can strike the building.  By installing air terminals, the sphere cannot touch the building because electrical charges flow through the lightning protection system into the ground.
• The radius of the rolling sphere is correlated with the peak value of the current in the lightning that strikes the structure: r = 10xIx0.65 where I define as kA.
• In the rolling sphere method, the radius of the sphere is selected in such a way that its radius is equal to the striking distance. Since the striking distance is a function of the prospective return stroke current, the radius of the sphere “r” is defined as a function of the probable return stroke current according to the relationship between the lightning striking distance and the peak return stroke current.
• The lightning stroke depends on the degree of risk considered.  So, for a high-risk facility, the sphere radius is at its smallest, e.g. 20meter or a 40meter diameter ball. The smallest size ball means the amount of protection installed will be at its highest. Thus, lowering the risk profile and increasing the protection afforded.
• For a low-risk scenario method, the sphere radius is at its largest distance, 60 meters (120-meter diameter ball), which means a lot less hardware to install.
• The radius r of the rolling sphere depends on the class of LPS as per given Table.

• Figure shows the application of the rolling sphere method to different types of structures. The sphere of radius r is rolled around and over all the structure until it meets the ground plane or any permanent structure or object in contact with the ground plane which can act as a conductor of lightning.
• A striking point could occur where the rolling sphere touches the structure and at such points protection by an air-termination conductor is required.
• Any part of the structure that is in contact with the sphere is considered to be vulnerable to a direct lightning strike; the untouched volume defines a lightning protected zone.

• When the rolling sphere method is applied to the structure, the structure should be considered from all directions to ensure that no part protrudes into an unprotected zone a point which might be overlooked if only front, side and plan views on drawings are considered.

PENETRATION DISTANCE:

• The distance between the two air terminals should be chosen in such a way that protection is provided for all the objects placed on the surface to be protected.
• The protection of the objects placed on the surface can be ensured by calculating the penetration distance of the rolling sphere.
• The distance between the level of air terminals and the least point of sphere in the space between the air terminals is called penetration distance.

• Let us consider an object of height ‘h’ placed on the surface to be protected. Let ‘ht’ be the height of the air terminal, ‘p’ be the penetration distance and ‘d’ be the distance between the two terminals.
• In this case, the penetration distance ‘p’ should be less than the physical height of the air-termination rods above the reference plane minus the height of the objects to be protected.
• P<(ht-h)

DISTANCE BETWEEN TWO AIR TERMINALS:

• The penetration distance of the rolling sphere below the level of conductors in the space between the conductors can be calculated by using the below formula (IS 62305-3).
• p=r-√(r^2-(d/2)^2 )
• Were,
• p : penetration distance
• r : radius of rolling sphere
• d: distance between the air terminals
• For attaining a particular penetration distance, we can derive the required distance between the air terminals from the above equation.
• d=2x√(2 x p x r-p^2 )
• If there are no objects protruding from the structure to be protected, then the penetration distance can be increased up to the height of the air terminal to provide maximum protection. At this condition, the distance can be calculated by substituting the value of height of air terminal (ht) in place of penetration distance (p).
• d=2x√(2 x ht x r-ht^2 )
• The distance between the air terminals(d) in rolling sphere method depends on two factors.
• Height of the air terminal and
• Radius of the rolling sphere
• Among these two factors, the radius of rolling sphere is a constant value which depends on the class of LPS as specified by IS/IEC 62305-3. Hence for particular class of LPS, the distance between the air terminals purely depends on the height of air terminal.

• Example:
• Conclude the equipment installed on Terrace is whether protected by LPS System or not by LPS system installed on Building (Calculate penetration height) having following details.
• LPS Level is -IV (Low Risk).
• The maximum height of equipment is 1 meter from Terrace Floor.
• The distance between the two Air terminals is 10 meters.
• Height of Air Terminal is 2 Meter.
• Calculation:
• First, we calculate the maximum distance between two Air terminal according to LPS level.
• Here Height of Air terminal (ht)= 2Meter.
• Height of equipment (h)=1 Meter
• According to LPS-IV Radius of rolling sphere (r) = 60 meter
• Distance between two Air terminals (d) =2√(2*ht*r-ht^2 )
• Distance between two Air terminals (d) =2√(2x2x60-2^2 )
• Distance between two Air terminals (d) =30.72 Meter
• Distance between actual installed Air terminals is 10 meter which is less than maximum calculated distance between two Air terminals.
• Now to calculate penetration height.
• penetration height (p)=r-√(r^2-(d/2)^2 )
• penetration height (p)=60-√(60^2-(10/2)^2 )
• penetration height (p)=0.20 Meter.
• Now Height of Air terminal (ht)-Height of equipment(h) = 2-1 =1Meter.
• Check condition of P< (ht-h)
• Here 0.2 <1 meter
• Hence equipment installed on terrace which height is 1 meter is protected from installed LPS System.

SIDE FLASHES IN TALL STRUCTURE

• On all structures higher than the rolling sphere radius “r”, flashes to the side of structure may occur. Each lateral point of the structure touched by the rolling sphere is a possible point of strike. However, the probability for flashes to the sides is generally negligible for structures lower than 60 meters.
• For taller structures, a major part of all flashes will hit the top, horizontal leading edges and corners of the structure. Only a few percentages of all flashes will be to the side of the structure.
• The probability of flashes to the sides decreases rapidly as the height of the point of strike on tall structures when measured from the ground.
• Therefore, consideration should be given to install a lateral air-termination system on the upper part of tall structures (typically the top 20 % of the height of the structure). In this case the rolling sphere method will be applied only to the positioning of the air-termination system of the upper part of the structure.

(1) Buildings Taller Than 120-meter High

• For structures taller than 120 meters, the standard recommends that all parts above 120 meters be protected. It is expected that due to the height and nature of such a structure, it would require a design to LPL I or II (99% or 97% protection level).
• For tall buildings, the actual risk of flashes to the side are estimated by the industry to be less than 2%, and typically these would be the smaller lightning flashes, e.g., from branches of the downward leader. Therefore, this recommendation would only be appropriate for high-risk locations or structures.

(2) Buildings Above 60-meter High

• In the IEC standards, for buildings above 60-meter, protection is required to the sides of the upper 20% of height. The same placement rules used for roofs should apply to the sides of the building.
• While the mesh method is preferable, particularly if using natural components, protection is permitted using horizontal rods and rolling sphere method. However, horizontal rods on most structures are impractical due to window washing access equipment, etc.

(3) Buildings Less Than 60-meter High

• Note that for structures less than 60 meters high the risk of flashes to the sides of the building is low, and therefore protection is not required for the vertical sides directly below protected areas.

(4) Buildings Taller Than 30 meters:

• For buildings taller than 30 m, additional equipotential bonding of internal conductive parts should occur at a height of 20 m and every further 20 m of height. Live circuits should be bonded via SPDs.

(C) THE MESH METHOD (Suitable for all flat surface building)

• The mesh method is the simplest and most flexible method for LPS because it does not depend on the height of the structure. However, it requires flat but non curved surfaces. The Flat surface may be horizontal or vertical surfaces.
• It is mostly used for simple Building like domestic households, mainly for perfectly square or rectangular buildings.
• In the mesh method, a mesh is created by a flat conductor and placed on the structure. The separation distance of the conductors is based upon the class of protection determined during the risk assessment.
• Mesh Size:
• According to IEC 62305, mesh conductor size is based on the selected class of LPS and that is totally dependable on user requirements.
• In the Mesh method, a conducting mesh with a cell size determined by the minimum return stroke current that is allowed to strike the protected structure.
• In order to avoid a direct strike, the mesh has to be located at a critical distance above the flat surface to be protected. This procedure is called “protective mesh method”.
• The maximum mesh size should be in accordance with the table below.

• The following conditions shall be considered while selecting the Mesh Method.
• (a) Air-termination conductors are positioned, on roof edge lines, on roof overhangs, on roof ridge lines, if the slope of the roof exceeds 1/10.
• (b) The mesh dimensions of the air-termination network are not greater than the values given in Table.
• (c) The network of the air-termination system is constructed in such a way that the lightning current will always encounter at least two distinct metal routes to earth-termination.
• (d) No metal installation protrudes outside the volume protected by air-termination systems.
• (e) The air-termination conductors follow, as far as possible, the shortest and most direct
• Location of Mesh
• The corners and edges of roofs are most susceptible to damage due to lightning. Therefore, designers and installers should place the conductors as close to the edge of the roof as possible.
• IEC 62305 allows for the use of conductors under the roof of a structure. Thus, the natural components of a structure can be used as part of the mesh grid, or even the whole grid. These components may be the rebar structure underneath the roof or dedicated lightning protection conductors, but they must be connected to the air termination rods that are mounted above the roof.
• For structures, with a protruding metallic structure, the Protective Angle Method is generally used as a supplement to the Mesh Method

•  Mesh Method with combination of other Methods:
• For Medium to large scale buildings mesh can be implemented, but due to its limitations, it does not come alone. It must be merged with other types of LPS, either protection angle or rolling sphere, subject to the suitable class number of each type.
• Air termination conductors and down conductors should be inter-connected by means of conductors at the roof level to provide sufficient current distribution over the down conductors.
• Conductors on roof and the connections of air termination rods may be fixed to the roof using both conductive or non-conductive spacers and fixtures. The conductors may also be positioned on the surface of a wall if the wall is made of non-combustible material. The fixing centers shall be minimum 1 meter apart.
• For each non-isolated LPS, the number of down conductors shall be not less than two. A down conductor should be installed at each exposed corner of the structure, where this is possible.

• Limitations:
• The mesh method is suitable for horizontal and inclined roofs with no curvature.
• The mesh method is suitable for flat lateral surfaces to protect against side flashes.
• If the slope of the roof exceeds 1/10, parallel air-termination conductors, instead of a mesh, may be used provided the distance between the conductors is not greater than the required mesh width.

Basic of External Lightning Protection System (LPS)-(Part-1)

Introduction:

• A lightning protection system does not attract or prevent a lightning strike. but the lightning protection system provides a low impedance path to lightning currents to flow from Lightning striking Point to the ground to prevent dangerous flashovers and lightning-caused fires.
• Lightning protection systems are designed to protect structures, equipment or people from the damaging effects of lightning strikes. These systems create pathways for lightning strikes to travel safely from the top of a structure to the ground with a lightning conductor. They protect the internal electrical components of a building by preventing fires or electrocution for that all metallic installations in the building must be made at equal potential.
• The basic goal of LPS is to prevent thermal, mechanical, and electrical effects that can cause damage to the protected structure or to humans via touch or step voltages within the structure.

Lighting Protection Standards:

• There are various lighting protection standards. Widely use are
• IEC 62305
• IS 2309
• NFPA 780
• NBC-2016

 IEC:62305 -Part 1 to 5:

COMPARISON BETWEEN IEC AND IS STANDARD FOR LPS: 

Lighting Protection Levels:

• Lighting Protection Level are divided into four categories. For each category, a set of maximum and minimum lightning current parameters is fixed (LPL I to IV).
• The maximum values of lightning current parameters are used to design lightning protection components (e.g. Cross section of conductors, thickness of metal sheets, current capability of SPDs and Separation distance against dangerous sparking).
• The minimum values of lightning current amplitude for the different LPL are used to derive the Rolling Sphere Radius to define the Lightning Protection Zone (LPZ0B) which cannot be reached by direct strike.

Types of Lighting Protection System (LPS):

• There are two types of Lightning Protection System
• External Lighting Protection
• Internal Lighting Protection.
• External lightning protection
• External lightning protection protects buildings in case of a direct lightning strike. It basically intercepts direct lightning flashes to the structure and conduct the lightning current from the point of strike to the ground and creates a protective sheath around the building which prevents it from catching fire and protects the people within.
• The External LPS also disperses this current into the earth without causing damage to the structures or causing unsafe potential rise / sparking.

• Internal Lighting Protection:
• An Internal LPS protects equipment against transient voltages and currents.
• Internal Lighting Protection / Surge protection provides safety within the building. It keeps surges which might enter the house via power supply cables / Power Line and protect electrical /electronic devices of house (which would otherwise be at risk via these routes).

Types of External LPS System

• There are two types of External LPS System
• Non-Conventional System / Early Streamer Emission (Isolated System)
• Conventional System (Non-Isolated System)
• Non-Conventional / Early Streamer Emission (Isolated System):
• Non-Conventional System / Isolated System does not mean that the system is electrically isolated from earth (a common misconception). It just means of physical distance achieved between the lightning current and the item being protected.
• In Non-Conventional / Isolated System, Lightning conductor does not directly attach to the structure or asset being protected. There is little or more separation between Structure and Lightning system.
• This can be achieved with free-standing masts (or poles) which stand someway off the item being covered at highest Point. Or, in some cases, separation can be achieved by using non-sparking conductors.
• Lightning Rods are installed at the highest point of protected building with sufficient separation distance to each other electrically and physically. Separate (Isolated) Lighting Rod provides conductive path to lighting current to the earth.
• Conventional (Non-Isolated System):
• In Conventional / Non-isolated System is typically attached conductor arrangements directly to the structure or asset being protected with little or no separation.

Components of External Lighting Protection System:

• An external Lightning Protection System has following parts

1. Air terminal system= Intercept a lightning flash to a structure
2. The down conductor system =provides the safest path to the lightning current towards the earth.
3. Earthing system =Disperse the lightning current into the earth.

• These individual elements of an LPS should be connected using appropriate lightning protection components. This will ensure that in the event of a lightning current discharge to the structure, any potential damage to the structure protected will be minimized.
• In most cases, the external LPS may be attached to the structure to be protected. An isolated LPS is preferred for areas at risk of explosion and fire.

(1) Air Termination System:

• The role of an air termination system is to capture the lightning discharge current and dissipate harmlessly to earth via down conductor and earth termination system. Therefore, it is very important to use a correctly designed Air-termination system.
• Air Termination System can be composed of any combination of the following elements.
• (i) Rods (including free standing masts)
• (ii) Catenary wires (suspended wires)
• (iii) Meshed conductors that may lie in direct contact with the roof or be suspended above it.

AIR TERMINATION SYSTEM DESIGN

•  As per considering Class of Lighting Protection System, the air-termination system shall be design by following methods.
• All methods should be used, independently or in any combination to ensure that the protection zones by different parts of the air-termination overlap and ensure that the structure is entirely protected.
• Methods for the air-termination for Lighting Protection System is
• (A) Protection Angle Method
• (B) Rolling Sphere Method and
• (C) Mesh Method
• All three methods may be used for the design of an LPS. The choice of the method depends on a practical evaluation of its suitability and the vulnerability of the structure to be protected.
• The major difference in Air Termination methods is as below.
• (i) The protection angle method is suitable for simple structures or for small parts of bigger structures. It also has limitations on the height of the air terminal. This method is not suitable for structures higher than the radius of the rolling sphere relevant to the protection level of the LPS.
• (ii) The rolling sphere method is suitable for complex shaped structures. This method is mostly used in all the cases.
• (iii) The mesh method is for general purposes, and it is particularly suitable for the protection of plane surface.

(A) PROTECTION ANGLE METHOD (Suitable for Simple-Shaped building)

• The Protection Angle method is wider used compared to mesh method, because it can be installed at simple structure, on not smooth/not flat surface, on protruding metallic structure.
• This method is used for structures that do not exceed 15 Meter in height.
• For structures less than 7.5 Meter in height, a Protection angle shall be 60 degrees, or 1:2, angle is permitted.
• For structures over 7.5 Meter but not in excess of 7.5 Meter a Protection angle shall be 45 degrees, or 1:1, angle is used. This is illustrated in Figure
• The Protective Angle Method is generally used as a supplement to the Mesh Method.
• Air-termination rods should be positioned so that all the parts of the structure, including metallic equipment installed on the roof like HVAC units, PV panels to be protected inside the envelope generated by the air-termination rods.
• In this method several air terminals are placed at the highest points on top of buildings/structures at different locations. Each air terminal covers a certain angle of protection.
• The degree of protection can be selected based on the height of terminal from base to tip. For example, if class I is selected, this means that the angle of protection is 70 degrees, considering 2 meters height of the terminal.
• In the case of installing metallic equipment’s, like HVAC Unit, PV panels at roof, sufficient distance among the equipment and air terminals shall be considered to avoid sparking, as well as selecting the appropriate protection angle.
• The real physical dimension of metal Air-termination shall be considered to calculate area protected by Lighting terminal. Typically, if the air rod is 5 meters tall, then the zone of protection offered by this air terminal rod would be based on 5 meters and the relevant class of LPS.
• If the building height is less than 30 meters, 45-degree cone of protection can be used. For building height more than 30 Meters, 30-degree cone of protection shall be considered

Volume protected by a vertical rod air-termination system

• Air-termination conductors, rods, masts and wires should be positioned so that all parts of the structure to be protected are inside the envelope surface generated by projecting points on the air-termination conductors to the reference plane, at an angle α to the vertical in all directions.
• The volume protected by a vertical rod is assumed to have the shape of a right circular cone with the vertex placed on the air-termination axis, semi-apex angle α, depending on the class of LPS, and on the height of the air-termination system as given in Table.

• The protection angle should confirm to the table mentioned below, with h being the height of the air-termination above the surface to be protected.

• Air termination conductors and down conductors should be inter-connected by means of conductors at the roof level to provide sufficient current distribution over the down conductors.
• Conductors on roof and the connections of air termination rods may be fixed to the roof using both conductive or non-conductive spacers and fixtures. The conductors may also be positioned on the surface of a wall if the wall is made of non-combustible material. The fixing centers shall be minimum 1 meter apart.
• For each non-isolated LPS, the number of down conductors shall be not less than two.
• A down conductor should be installed at each exposed corner of the structure, where this is possible.

Limitation:

• The protection angle method has geometrical limits and cannot be applied if Building height (H) is larger than the rolling sphere radius (r).
• The angle will not change for values of Building height (H) below 2 meters.