Lightning Protection System (LPS)-(Part-3)

COMPARISION OF VARIOUS PROTECTION METHOD

COMPARISION OF VARIOUS PROTECTION METHOD
Protection Method	Type of Structure
	Simple structure	Complex shaped structure	Plane Structure
Protection Angle	(*) YES	NO	NO
Mesh Method	NO	YES	YES
Rolling sphere Method	YES	YES	YES
(*) This method is not suitable for structure height more than radius of the rolling sphere relevant to the selected protection level of LPS

(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.

DISTANCE BETWEEN DOWN CONDUCTORS
(IEC/BS EN 62305-3 Table 4)
Class of LPS	Distance between conductors
CLASS I- (Very High Risk)	10 Meter
CLASS II- (High Risk)	10 Meter
CLASS III- (Moderate Risk)	15 Meter
CLASS IV- (Low Risk)	20 Meter

• 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.

Minimum Size of Down conductor
Protection level	Material	Section
I-IV	Steel	50 mm2
I-IV	Aluminum	25 mm2
I-IV	Copper	16 mm2

• 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.

Suggested fixing centers
Table E.1 IEC- 62305-3
Arrangement	Fixing centers for tape and stranded conductors (mm)	Fixing centers for round solid conductors (mm)
Horizontal conductors on horizontal surfaces	500 mm	1000 mm
Horizontal conductors on vertical surfaces	500 mm	1000 mm
Vertical conductors from the ground to 20 m	1000 mm	1000 mm
Vertical conductors from 20 m and thereafter	500 mm	1000 mm
NOTE: Assessment of environmental conditions (i.e. expected wind load) should be undertaken and fixing centers different from those recommended may be found to be necessary.

(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.

Horizontal & Vertical electrode Length for Type A & Type-B earth electrode (based on soil resistivity)
IEC- 62305-3
Class of LPS	<500 Ωm			<1000 Ωm		<2000 Ωm		<3000 Ωm
	Horizontal electrodes (l1)	Vertical electrodes 0.5 x I1	Horizontal electrodes (l1)		Vertical electrodes 0.5 x I1	Horizontal electrodes (l1)	Vertical electrodes 0.5 x I1	Horizontal electrodes (l1)	Vertical electrodes 0.5 x I1
I	5 Meter	2.5 Meter	20 Meter		10 Meter	50 Meter	25 Meter	80 Meter	40 Meter
II	5 Meter	2.5 Meter	10 Meter		5 Meter	30 Meter	15 Meter	45 Meter	22 Meter
III	5 Meter	2.5 Meter	5 Meter		2.5 Meter	5 Meter	2.5 Meter	5 Meter	2.5 Meter
IV	5 Meter	2.5 Meter	5 Meter		2.5 Meter	5 Meter	2.5 Meter	5 Meter	2.5 Meter

• 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