NOTE The rolling sphere should not touch any part of the metallic roof including the standing seams.
Figure E.26 - Construction of air-termination network on a roof with conductive
covering where puncturing of the covering is not acceptable
Non-conductive as well as conductive supports are allowed.
When conductive supports are used, the connection to the roof-sheet should withstand partial lightning current (see Figure E.26).
Figure E.24 shows an example of natural air-termination using a roof parapet as the airtermination conductor at the edge of the roof area.
Flush-mounted and protruding structures on the roof surface should be protected by means of air-termination rods. Alternatively, extraneous metalwork should be bonded to the LPS unless it conforms to 5.2.5.
Figure Е.27 gives an example of the connection of the air-termination with the natural downconductors in concrete.
Key
air-termination rod
horizontal air-termination conductor
down-conductor
T-type joint
cross type joint
connection to steel reinforcing rods (see E.4.3.3 and E.4.3.6)
test joint
type В earthing arrangement, ring earth electrode
flat roof with roof fixtures
T-type joint - corrosion resistant
NOTE The steel reinforcement of the structure should comply with 4.3. All dimensions of the LPS should comply with the selected protection level.
Figure E.27 - Construction of external LPS on a structure of steel-reinforced
concrete using the reinforcement of the outer walls as natural componentsЕ.5.2.4.2.1 Lightning protection for multi-storey car park roofs
For the protection of this type of structure, air-termination studs may be used. These studs can be connected to the reinforcement steel of a concrete roof (see Figure E.28). In the case of roofs where a connection to the reinforcement cannot be made, the roof conductors can be laid in the seams of the carriageway slabs and air-termination studs can be located at the mesh joints. The mesh width shall not exceed the value corresponding to the protection class given in Table 2. In this case, the persons and vehicles on this parking area are not protected against lightning.
IEC 2705/10
Key
air-termination stud
steel conductor connecting to several bars of the reinforcement steel
steel reinforcement to concrete
Figure E.28 - Example of an air-termination stud used on car park roofs
If the topmost parking area is to be protected against direct lightning strikes, air-termination rods and/or overhead air-termination wires should be employed
.
ІЕС 2706/10
Key
protection cone
metallic roof fixture
horizontal air-termination conductor
electric power installation line, preferably enclosed in a conductive shield
electric equipment
separation distance according to 6.3
a protection angle, see Table 2
NOTE The height of the air-termination rod should comply with Table 2.
Figure E.29 - Air-termination rod used for protection of a metallic roof fixture with
electric power installations which are not bonded to the air-termination system
In the case of vertical conductors, the area which is possible to reach by hand should be taken into account. The necessary separation distance can be achieved either by provision of barriers or by protective wiring.
Signs should be provided at the entrances drawing attention to the danger of lightning strikes during thunderstorms.
The touch and step voltages may be disregarded if the roof is covered by a layer of asphalt of at least 50 mm thickness. Additionally, the step voltages may be disregarded if the roof is constructed of reinforced concrete with interconnected reinforcement steel with continuity conforming to 4.3.
E.5.2.4.2.2 Flat-roofed, steel-reinforced concrete structures with roofs not accessible to the public
On a flat roof not accessible to the public that incorporates an external air-termination system, air-termination conductors should be installed as shown in Figure E.27. For the equipotential ring conductor on the roof, the metal cladding on the roof parapet may be used as shown in Figure E.24 and Figure E.30.
Key
1 corrosion-resistant joint
2 flexible conductor
3 metallic covering of the parapet
NOTE Special attention should be paid to the proper selection of materials and good design of joints and bridging conductors to avoid corrosion.
Figure E.30 - Method of achieving electrical continuity on metallic parapet capping
Figure E.27 shows a method of installing meshed conductors on a roof.
When temporary mechanical damage of the waterproof layer on the roof of a structure is acceptable, the air-termination mesh covering the flat area of the roof may be replaced with natural air-termination conductors consisting of steel reinforcement bars in concrete according to 5.2.4. An acceptable alternative is that the LPS air-termination conductors may be fixed directly on the concrete roof.
In general, a lightning flash to the reinforcement of a concrete roof will damage the waterproof layer. Rainwater may then cause corrosion of the steel-reinforcing rods leading to damage. If reduction in the mechanical strength of concrete due to the corrosion is not permitted, an airtermination system should be installed and preferably bonded to the reinforcement steel, preventing direct lightning flashes to the steel-reinforced concrete.
Metal covering that is provided for mechanical protection of outer walls (parapet capping) may be used as a natural component of the air-termination according to 5.2.5 if there is no risk of fire ignition by melting metal.
Roof coverings of conductive sheets not conforming to Table 3 may be used as airtermination conductors where melting at the point of lightning flashes can be tolerated. If not, the conductive roof sheeting should be protected by an air-termination system of sufficient height (see Figures E.20 and E.26). In this case, the rolling sphere method should be applied. To conform to this method the mesh size has to be smaller and the supports higher than that for an ordinary mesh air-termination system.
When conductive supports are used, the connection to the roof-sheet should withstand partial lightning current.
Figure E.24 shows an example of a natural air-termination using a roof parapet as the airtermination conductor at the edge of the roof area.
When it is acceptable for temporary damage to the facade to occur, and shattered parts of up to 100 mm of broken concrete to fall down from the structure, 5.2 permits the ring conductor on the roof to be replaced by a natural ring conductor consisting of steel reinforcement in concrete.
Metal parts which do not satisfy the conditions of air-terminations stipulated in 5.2.5 may, however, be used to connect the different lightning-current-carrying parts within the domain of the roof area.
E.5.2.4.2.3 Provision of adequate structure shielding
The outer walls and roof of a structure may be used as an electromagnetic shield in order to protect electrical and information-processing equipment within the structure (see Annex В of IEC 62305-2:2010 and IEC 62305-4).
Figure E.27 provides an example of a steel-reinforced concrete structure using the interconnected reinforcing steel as down-conductors and as electromagnetic shielding of the enclosed space. For more details see IEC 62305-4.
Within the domain of the air-termination system on the roof, all conductive parts with at least one dimension larger than 1 m should be interconnected to form a mesh. The meshed shield should be connected to the air-termination system at the roof edge and also at other points within the roof area in accordance with 6.2.
Figures E.24 and E.30 show the construction of air-terminations on structures with conductive skeletons using a roof parapet as a natural air-termination and the steel skeleton as natural down-conductors.
In Figure E.30 an example is given of how to provide electrical continuity of natural components in an LPS.
As a result of the reduced mesh size of steel structures compared with Table 2, the lightning current is distributed over several parallel conductors, resulting in a low electromagnetic impedance and consequently in accordance with 6.3, the separation distances are reduced and the necessary separation distances between the installations and the LPS are not required.
In most structures the roof is the least shielded part of the structure. Therefore particular attention should be paid to improve the shielding efficiency of roof constructions.
When no conductive structural elements are incorporated in the roof, shielding may be improved by reducing the spacing of the roof conductors.
Е.5.2.4.2.4 Protection of flush-mounted or protruding roof fixtures
Air-termination rods for the protection of metal, flush-mounted roof fixtures or protruding roof fixtures should be of such height that the fixture to be protected lies fully within the rolling sphere protection space of the air-termination rod or is fully within the cone of the protection angle in accordance with Table 2. The separation distance between the air-termination rods and the roof fixtures should be such that the proximity condition stipulated in 6.3 is satisfied.
Figure E.29 shows an example of roof fixture protection by air-termination rods using the protection angle air-termination design method. The value of the protection angle shall be consistent with the protection level of the LPS stipulated in Table 2.
Metal roof fixtures, not protected by air-termination rods, do not require additional protection if their dimensions do not exceed all of the following values:
height above the roof level 0,3 m;
the total area of the fixture 1,0 m2;
the length of the fixture 2,0 m.
Metal flush mounted roof fixtures not fulfilling these requirements and not being within the requirements for the separation distance according to 6.3 should be bonded to the airtermination system with at least one bonding conductor.
Non-conductive roof fixtures which are not within the protected volume by air-termination rods and which do not protrude by more than 0,5 m above the surface formed by the airtermination system do not require additional protection from air-termination conductors.
Conductive installations, such as electrical conductors or metallic pipes, which lead from flush-mounted roof fixtures into the interior of the building, can conduct a considerable portion of the lightning current into the interior of the building. Where such conductive connections exist, the protruding fixtures on the roof surface should be protected by air-termination systems. If protection by means of an air-termination system is not possible or cost-effective, isolated parts, with lengths corresponding to at least twice the specified separation distance, can be installed in the conductive installations (e.g. compressed air pipes).
Chimneys of non-conductive material should be protected by means of air-termination rods or air-termination rings when they are not within the protection space of an air-termination system. The air-termination rod on a chimney should be of such height that the complete chimney lies within the protection space of the rod.
A lightning flash to a non-conductive chimney is possible when the chimney is not situated within the protection space of an air-termination system, due to the fact that the inner surface of the chimney is covered by a soot deposit possessing a conductivity such that, even in the absence of rain, it is capable of conducting the current of a streamer discharge of great length.
Figure E.22b shows the construction of an air-termination rod on a chimney made of isolating bricks.
E.5.2.4.2.5 Protection of roof fixtures enclosing electrical or information-processing equipment
All roof fixtures of non-conductive or conducting material, which contain electrical and/or information-processing equipment, should lie within the protection space of the air-termination system.
A direct flash into equipment installed inside the protection space of the air-termination system is improbable.
A direct flash into the roof fixture would lead not only to its destruction but would also cause extended damage to the connected electrical and electronic equipment not only in the roof fixtures, but also inside the building.
Roof fixtures on steel structures should also lie in the protection space of the air-termination system. In this case protruding air-termination conductors should be bonded not only to the air-termination system but also to the steel structure directly, if possible. When bonded to the structure they need not conform to the separation distance.
The requirements for roof fixtures should also apply to fixtures installed on vertical surfaces to which a lightning strike is possible, i.e. which can be touched by the rolling sphere.
Figure E.29 and Figure E.31 contain examples of air-termination constructions which protect the roof fixtures of conducting and isolating material enclosing electrical installations.
Figure E.31 is only suitable if the separation distance, s, cannot be maintained.
Key
1 air-termination conductor
2 metallic cover
3 bonding conductor
4 horizontal air-termination conductor
5 electric equipment
6 electric power junction box with SPD
7 down-conductor
I EC 2708/10
NOTE The enclosed electric equipment is bonded to the air-termination system complying with Є.5.2.4.2.6, through the metallic cable shield withstanding a substantial part of the lightning current.
Figure E.31 - Metallic roof fixture protected against direct lightning interception,
connected to air-termination system
NOTE If the fixtures need extra protection, SPDs on the active cables connected to it can be provided at roof level.
The required separation distance should be maintained not only in air but also for the path through solid material (km= 0,5).
E.5.2.4.2.6 Electrical installation protruding from the space to be protected
Antenna on the roof of a structure should be protected against direct lightning flashes by installing the antenna in an already protected volume.
The antenna system should be integrated into the LPS ( see also IEC 60728-11 [6!.
An isolated external LPS (see Figure E.32a) or a non-isolated external LPS (see Figure E.32b) may be used.
In this latter case, the antenna mast should be bonded to the air-termination system. Then partial lightning currents will be treated as being inside the structure to be protected. The antenna cable should enter the structure preferably at the common entrance for all services or near the main LPS bonding bar. The antenna cable conductive sheath should be bonded to the air-termination system at roof level and to the main bonding bar.
Roof fixtures housing electrical equipment for which the separation distance cannot be maintained, should be bonded to the air-termination system and to the conductive elements of the roof fixtures and the conductive shield of its electrical equipment in accordance with Table 9.
Figure E.31 is an example of the method of bonding a roof fixture with conductive parts to an electrical installation and the air-termination of a structure.
ІЕС 2709/10
Key
metallic mast
isolator
air-termination rod
air-termination conductor
bonding conductor
antenna cable
test joint
equipotential bonding bar
foundation earth electrode
a protection angle
s separation distance
I length to be considered for separation distance calculation
MDB main distribution box
PCB power connection box
Figure E.32a -TV antenna mast and antennas protected with isolated air-terminations planned
according to the protection angle method
ІЕС 2710/10
Key
metallic mast
horizontal air-termination conductor on the ridge of the roof
joint between the roof down-conductor and the metallic antenna mast
antenna cable
the main bonding bar; metallic shield on the antenna cable is connected to the bonding bar
test joint
TV
parallel routing of the antenna cable and the electric power cable
electric power cable
earth-termination system
the main electric power distribution box with SPD
foundation earth electrode
LPS conductor
a protection angle
/ length to be considered for separation distance calculation
NOTE For small structures only two down-conductors may be sufficient, according to 5.3.3.
Figure E.32b -TV antenna using the mast as an air-termination rod
Figure E.32 - Examples of lightning protection of a house with a TV antenna
E.5.2.4.2.7 Protection of conductive parts on the roof
Conductive items, such as those with insufficient wall thickness, which cannot withstand lightning strikes and which are installed on roofs, and also conductive roof coverings or other parts on structures which do not meet the requirements for natural air-termination systems according to 5.2.5 and Table 3, and in which a lightning flash cannot be tolerated, should be protected by air-termination conductors.
For the design of the lightning protection for conductive parts on the roof the rolling sphere air-termination design method should be applied (see Figure E.33).
Key
rolling sphere
air-termination rod
electric equipment
down-conductor
metallic vessel
r radius of the rolling sphere, see Table 2
s separation distance according to 6.3
Figure E.33 - Installation of lightning protection of metallic equipment
on a roof against a direct lightning flash
Figure Е.31 is an example of the design of an air-termination system protecting a conductive roof fixture against a direct lightning flash when the separation distance, s, cannot be maintained.
E.5.2.4.2.8 Protection of structures covered by soil
For structures incorporating a layer of soil on the roof and where people are not regularly present, a normal LPS may be utilized. The air-termination system should be a meshed airtermination system on top of the soil, or a number of air-termination rods, connected by a buried mesh, conforming to the rolling sphere or protection angle method. If this is not possible, it should be recognized that a buried meshed air-termination system without rods or finials will offer a reduced interception efficiency.
Structures with a roof layer of soil up to 0,5 m where people are regularly present, will need a meshed air-termination system with meshes of 5 m x 5m to prevent dangerous step voltages. To protect the people on the ground from direct lightning flashes, air-termination rods conforming to the rolling sphere method, may also be necessary. These rods can be replaced by natural air-termination components, such as fences, lighting masts, etc. The height of the air-termination systems shall take into account people’s height allowance of 2,5 m along with the necessary separation distances (see also Figure E.3).
If nothing of the kind is available, people should be made aware that during a thunderstorm they may be exposed to a direct lightning flash.
For underground structures with a layer of soil over 0,5 m, measures are under consideration. As long as there is no research available, it is advisable to use the same measures as for layers of soil up to 0,5 m.
For underground structures containing explosives materials, an additional LPS shall be required. Such an additional LPS may be an isolated LPS over the structure. The earthing systems of both protection measures should be interconnected.
E.5.2.5 Natural components
On structures with flat roofs, the metal covering of a roof parapet represents a typical natural component of an LPS air-termination network. Such covering comprises extruded or bent parts of aluminium, galvanized steel or copper in U-form which protect the upper surface of the roof parapet against the influence of weather. The minimum thickness given in Table 3 shall be applied for such an application.
The air-termination conductors, conductors on the roof surface and the down-conductors should be connected to the roof parapet covering.
Conductive bridging should be provided at the joints between sections of parapet covering plates, unless there is good, reliable continuity between them.
Figure E.24 is an example of an air-termination construction using the conductive covering of parapets as a natural air-termination conductor of the LPS.
Conductive parts, such as metal tanks, metal pipework and railings mounted on or extending above a roof surface may be treated as natural components of an air-termination system provided their wall thickness conforms to Table 3.
Vessels and pipework, which contain gas or liquids under high pressure or flammable gas or liquids, should not be used as natural air-terminations. Where this cannot be avoided, the heating effects of lightning current should be taken into account when designing the pipework.
Conductive parts above the roof surface such as metal tanks are often naturally connected to equipment installed within the structure. In order to prevent conduction of the full lightning current through the structure, it is necessary to provide a good connection between such natural components of the LPS and the air-termination mesh.
Figure E.34 is an example which shows details of the bonding of conductive roof fixtures to air-termination conductors.
Key
1 air-termination conductor fixing
2 metallic pipe
3 horizontal air-termination conductor
4 steel reinforcement within concrete
NOTE 1 The steel pipe should comply with 5.2.5 and Table 6, the bonding conductor should comply with Table 6 and the reinforcement should comply with 4.3. The roof bonding should be watertight.
NOTE 2 In this particular case bonding is provided to the reinforcement of the reinforced concrete structure.
Figure E.34 - Connection of natural air-termination rod to air-termination conductor
Conductive parts above the roof surface such as metal tanks and steel reinforcing rods of concrete should be connected to the air-termination network.
When a direct lightning strike into the conductive part on the roof is not acceptable, the conductive part shall be installed inside the protection space of an air-termination system.
Conductive coverings on facades and equivalent parts of structures where the risk of fire is negligible should be treated in accordance with 5.2.5.
