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Figure E.5 shows correct welding of bonding conductors to the reinforcing rods of the reinforced concrete.

Where welding to the reinforcing rods is not permitted, clamps or additional dedicated conductors should be used. These additional conductors can be made of steel, mild steel, galvanized steel or copper. The additional conductors should be connected to a large number of reinforcing rods by lashings or clamps to take advantage of the shielding possibilities of the reinforcement steel.

E.4.3.7 Down-conductors

The reinforcing rods of walls or concrete columns and steel structural frames may be used as natural down-conductors. A termination joint should be provided on the roof to facilitate the connection of the air-termination system and, unless the reinforced concrete foundation is being used as the only earth-termination, termination joints should be provided to facilitate the connection with the earth-termination system.

When using a particular rod of the reinforcement steel as the down-conductor, care should be taken in the route to earth to ensure that the rod that is located in the same position will be used all the way down, thereby providing direct electrical continuity.

When the vertical continuity of the natural down-conductors, providing a straight path from roof to ground cannot be guaranteed, additional dedicated conductors should be used. These additional conductors should be lashed or clamped to the reinforcement steel.

Wherever there is doubt as to the most direct route for the down-conductor (i.e. for existing buildings) an external down-conductor system should be added.

Figures E.4 and E.8 show construction details of natural components in the LPS for reinforced concrete structures. See also E.5.4.3.2 for the use of the rods of reinforced concrete elements as foundation earth electrodes.

Key

1. metallic covering of the roof parapet

2. joint between facade plates and air-termination

3. horizontal air-termination conductor

4. metallic facade segment covering

5. equipotentialization bar of the internal LPS

6. joint between facade plates and to supporting frame

7. test joint

8. steel reinforcement in concrete

9. type В ring earth electrode

10. foundation earth electrode

An applicable example may utilize the following dimensions a = 5 m b = 5 m c=1m.

NOTE For the joints between the plates, see Figure E.35.

Figure E.8a - Use of a metallic facade covering as a natural down-conductor system
on a structure of steel-reinforced concrete

ІЕС 2674/10

Key

1. vertical frame

2. wall fixing

3. connectors

4. horizontal frame

Figure E.8b - Connection of facade supports

Figure E.8 - Use of metallic facade as natural down-conductor system
and connection of facade supports

Internal down-conductors in the individual columns and the walls should be interconnected by means of their steel reinforcing rods and should conform to the conditions for electrical continuity according to 4.3.

Steel reinforcing rods of individual prefabricated concrete elements and the reinforcing rods of concrete columns and concrete walls should be connected to the reinforcing rods of floors and roofs before the floors and roofs are cast.

Extensive continuously conductive parts exist within the reinforcing of all constructional elements, which are cast with concrete on site, for example, walls, columns, stairs and lift shafts. If floors are constructed of site-cast concrete, the down-conductors in the individual columns and walls should be interconnected by means of their reinforcing rods to ensure an even distribution of the lightning current. If floors are constructed of prefabricated concrete elements, such connections are generally not available. However, at little extra cost it is generally possible to prepare joints and terminations to connect the reinforcing rods of the individual prefabricated concrete elements to the reinforcing rods of the columns and walls before the floors are cast by insertion of additional connecting rods.

Prefabricated concrete elements used as suspended facades are not effective for lightning protection as bonding connections are not provided. If highly effective lightning protection is to be provided for equipment installed within a structure, such as office buildings with extensive information-processing equipment and computer networks, it is necessary for the reinforcing rods of such facade elements to be interconnected and connected to the reinforcing rods of the load-bearing elements of the structure in such a manner that the lightning current can flow through the complete outer surface of the structure (see Figure E.4).

If continuous strip windows are installed in the outer walls of a structure, it is essential that a decision be taken as to whether the connection of the prefabricated concrete parts above and below the continuous strip windows should be made by means of the existing columns or whether they should be interconnected at smaller intervals corresponding to the window pitch.

Extensive integration of conductive parts of the outer walls improves the electromagnetic shielding of the interior of the structure. Figure E.9 shows the connection of continuous strip windows to a metal facade covering.

IEC 2675/10

Key

1. joint between a facade plate segment and the metallic strip window

2. metallic facade plate

3. horizontal metallic strip

4. vertical metallic strip

5. window

Figure E.9 - Connection of the continuous strip windows to a metal facade covering

If steel structures are used as down-conductors, every steel column should be connected to the steel reinforcing rods of the concrete foundation by bonding points as shown in Figure E.7.

NOTE For more information on the use of steel reinforcement of structure walls for the purpose of electro­magnetic shielding, see IEC 62305-4.

In the case of large, low buildings such as halls, the roof is supported not only at the building circumference but also by internal columns. Conductive columns should be connected to the air-termination system at the top and to the equipotential bonding system at the floor, creating internal down-conductors; this to prevent dangerous sparking inside the building. Increased electromagnetic interference occurs in the vicinity of such internal down-conductors.

Steel skeleton constructions generally use steel roof girders connected by means of bolted joints. Provided the bolts are tightened with the force required to achieve mechanical strength, all bolted steel parts may be considered electrically interconnected. The thin paint layer is pierced by the lightning current on initial discharge thus forming a conductive bridge.

The electrical connection may be improved by baring the seating surface of the bolt heads, bolt nuts and washers. A further improvement can be achieved by provision of a welding seam approximately 50 mm long after completion of the structural assembly.

On existing structures with extensive conductive parts in/on the outer walls, the continuity of conductive parts should be established for use as down-conductors. This technique is also recommended when high demands on the cultural aspects of architectural design have to be maintained in addition to the demands for protection against LEMP.

Interconnected equipotentialization bars should also be provided. Each equipotentialization bar should be connected to the conductive parts in the outer walls and in the floor. This may already be provided by the horizontal reinforcing bars at the ground level and each subsequent floor level.

If possible, a connection point to the steel reinforcement in the floor or in the wall should be provided. The connection should be made to at least three reinforcing rods.

E.4.3.8 Equipotentialization

When a large number of bonding connections to the reinforcement is required at different floors and a significant interest is given to achieve current paths of low inductance utilizing the reinforcing rods of the concrete walls for potential equalization and for shielding of the inner space of the structure, ring-conductors should be installed within or outside the concrete on the separate floors. These ring conductors should be interconnected by means of vertical rods at intervals not greater than 10 m.

This arrangement should be given preference due to its greater reliability, especially where the magnitude of the interference current is unknown.

A meshed-connection conductor network is also recommended. Connections should be designed to carry high currents in the event of a fault in the energy supply.

In large structures, the equipotentialization bar acts as a ring conductor. In such cases connection points to the steel-reinforcing bars should be made every 10 m. No special measures other than those prescribed for the basement in 6.2.2 a) for connection of the structure reinforcement to the LPS are necessary.

E.4.3.9 Foundation as earth-termination

For large structures and industrial plants the foundation is normally reinforced. The reinforcing rods of the foundation, foundation slab and outer walls in the region below the soil surface of such structures form an excellent foundation earth electrode, provided the requirements of 5.4 are satisfied.

The reinforcing rods of the foundation and the buried walls can be used as foundation earth electrode.

This method achieves good earthing at minimum cost. In addition, the metal enclosure, consisting of the steel reinforcement of the structure, in general offers a good potential reference for the electric power supply, telecommunication and electronic installations of the structure.

In addition to the interconnection of the reinforcing rods by wire-lashing, the installation of an additional meshed metal network to ensure good joints is recommended. This additional network should also be lashed to the reinforcement steel. The terminal conductors for connections of external down-conductors or structure elements used as down-conductors and for connection of the earth-termination installed externally should be brought out of the concrete at suitable points.

In general, the reinforcing of a foundation is electrically conductive except in cases where gaps are provided between different parts of the structure to allow different settling rates.

Gaps between conductive structure parts should be bridged by bonding conductors conforming to Table 6 using clamps and joints in accordance with 5.5.

Reinforcing rods of concrete columns and walls standing on a foundation should be connected to the reinforcing rods of the foundation and to the conductive parts of the roof.

Figure E.10 shows the design of the LPS of a reinforced concrete structure for concrete columns, walls and a roof with conductive parts

.

1. LPS conductor passing a watertight bushing

2. steel reinforcement in a concrete column

3. steel reinforcement in concrete walls

NOTE The steel reinforcing of an internal column becomes a natural internal down-conductor when the steel reinforcing of the column is connected to the air-termination and the earth-termination of the LPS. The electromagnetic environment near the column should be considered when sensitive electronic equipment is installed near the column.

Figure E.10 - Internal down-conductors in industrial structures

When welding to reinforcing is not allowed, additional conductors should be installed in the columns, or the connections should be implemented by means of tested joints. These additional conductors should be lashed or clamped to the reinforcing steel.

After completion of construction and connecting all the services to the building via an equi­potential bonding bar, it will often be impossible (in practice) to measure the earthing resistance as part of the maintenance programme.

If in certain conditions it is not possible to measure the earthing resistance of the foundation earth, the installation of one or more reference earth electrodes close to the structure provide a possible method of monitoring the changes in the environment of the earthing system over the years by performing a circuit measurement between the earth electrode and the foundation earthing system. However, good equipotentialization is the main advantage of the foundation earthing system and the resistance to earth tends to be less important.

E.4.3.10 Installation procedures

All lightning protection conductors and clamps should be installed by the installer of the LPS.

Agreement should be reached with the civil works contractor in sufficient time to ensure that the time schedule for construction work is not exceeded as a result of delay in installation of the LPS before pouring the concrete.

During construction, measurements should be taken regularly and an LPS installer should supervise the construction (see 4.3).

E.4.3.11 Prefabricated reinforced concrete parts

If prefabricated reinforced concrete parts are used for lightning protection, e.g. as down­conductors for shielding or as conductors for potential equalization, connection points according to Figure E.7 should be attached to them to allow later interconnection of the prefabricated reinforcement with the reinforcement of the structure in a simple manner.

The location and form of connection points should be defined during the design of the prefabricated reinforced concrete parts.

The connection points should be located so that in the prefabricated concrete part a continuous reinforcing rod runs from one bonding joint to the next.

When the arrangement of continuous reinforcing rods in a prefabricated reinforced concrete part is not possible with standard reinforcing rods, an additional conductor should be installed and lashed to the existing reinforcement.

In general, one connection point and a bonding conductor is required at each corner of a plate-like prefabricated reinforced concrete part as illustrated in Figure E.11.

E.4.3.12 Expansion joints

When the structure comprises a number of sections with expansion joints, with allowance for settling of the structure sections, and extensive electronic equipment is to be installed in the building, bonding conductors should be provided between the reinforcement of the various structural sections across the expansion joints at intervals not exceeding one half of the distance between the down-conductors specified in Table 4.

In order to ensure low-impedance potential equalization and effective shielding of the space inside a structure, expansion joints between sections of a structure should be bridged at short intervals (between 1 m and one half of the distance between down-conductors) by flexible or sliding bonding conductors depending on the required shielding factor, as shown in Figure E.11.

Кеу

1 2

r

ІЕС 2677/10

einforced precast concrete

bonding conductors

F igure E.11a - Installation of bonding conductors on plate-like prefabricated reinforced
concrete parts by means of bolted or welded conductor links

1. expansion slot

2. welded joint

3. recess

4. flexible bonding conductor

A reinforced concrete part 1

В reinforced concrete part 2

Figure E.11b - Construction of flexible bonds between two reinforced
concrete parts bridging an expansion slot on a structure

Figure E.11 - Installation of bonding conductors in reinforced concrete structures
and flexible bonds between two reinforced concrete parts

Е.5 External lightning protection system

E.5.1 General

The positioning of external LPS conductors is fundamental to the design of the LPS and depends on the shape of the structure to be protected, the level of protection required and the geometric design method employed. The air-termination system design generally dictates the design of the down-conductor system, the earth-termination system and the design of the internal LPS.

If adjoining buildings have an LPS, those LPS, where permissible, should be connected to the LPS of the building under consideration.

E.5.1.1 Non-isolated LPS

In most cases, the external LPS may be attached to the structure to be protected.

When the thermal effects at the point of strike or on conductors carrying the lightning current may cause damage to the structure, or to the content of the structure to be protected, the spacing between LPS conductors and combustible material should be at least 0,1 m.

NOTE Typical cases are

- structures with combustible coverings, - structures with combustible walls.

E.5.1.2 Isolated LPS

An isolated external LPS should be used when the flow of the lightning current into bonded internal conductive parts may cause damage to the structure or its contents.

NOTE 1 The use of an isolated LPS may be convenient where it is predicted that changes in the structure may require modifications to the LPS.

An LPS that is connected to conductive structural elements and to the equipotential bonding system only at ground level, is defined as isolated according to 3.3.

An isolated LPS is achieved either by installing air-termination rods or masts adjacent to the structure to be protected or by suspending overhead wires between the masts in accordance with the separation distance of 6.3.

An isolated LPS is also installed on structures of isolating material, such as brickwork or wood, where the separation distance, as defined in 6.3, is maintained and no connection is made to conductive parts of the structure nor to equipment installed therein, with the exception of connections to the earth-termination system at ground level.

Conductive equipment within the structure and electrical conductors should not be installed with distances to the air-termination system conductors and to the down-conductors shorter than the separation distance defined in 6.3. All future installations should conform to the requirements of an isolated LPS. These requirements should be made known to the owner of the structure by the contractor responsible for the design and construction of the LPS.

The owner should inform future contractors performing work in or on the building about these requirements. The contractor responsible for such work should inform the owner of the structure if the contractor cannot meet these requirements.

All parts of equipment installed in a structure with an isolated LPS should be placed within the protected space of the LPS and satisfy the separation distance conditions. The LPS conductors should be mounted on isolated conductor fixtures, if conductor fixings attached directly to the structure walls are too close to conductive parts, so that the distance between the LPS and the inner conductive parts exceed the separation distance as defined in 6.3.

NOTE 2 Isolating fixtures should be equal to or longer than the separation distance, taking also into account environmental conditions.

Flush-mounted conductive roof fixtures which are not connected to the equipotential bonding and have a distance to the air-termination system not in excess of the separation distance but a distance to the equipotential bonding in excess of the separation distance, should be connected to the air-termination system of the isolated LPS. For this reason structures such as this should not be considered as isolating but as a structure with flush-mounted conductive roof fixtures which are not connected to the equipotential bonding

The design of an LPS and the safety instructions for work in the vicinity of a roof fixture should take account of the fact that the voltage on such fixtures will rise to that of the air­termination system in the event of a lightning strike.

An isolated LPS should be installed on structures with extensive interlinked conductive parts when it is desired to prevent lightning current from flowing through structure walls and internally installed equipment.

On structures consisting of continuously interlinked conductive parts such as steel construction or steel-reinforced concrete, the isolated LPS should maintain the separation distance to these conductive parts of the structure. To achieve adequate separation, LPS conductors may have to be fixed to the structure by isolation type conductor fixtures.

It should be noted, that columns and ceilings of reinforced concrete are often used in brick structures.

E.5.1.3 Dangerous sparking

Dangerous sparking between an LPS and metal, electrical and telecommunication installations can be avoided

• in an isolated LPS by isolation or separation according to 6.3,

• in a non-isolated LPS by equipotential bonding, according to 6.2, or by isolation or separation according to 6.3.

E.5.2 Air-termination systems

E.5.2.1 General

This standard does not provide any criteria for the choice of the air-termination system because it considers rods, stretched wires and meshed conductors as equivalent.

The arrangement of an air-termination system should be in accordance with the requirements of Table 2.

E.5.2.2 Positioning

For the design of the air-termination system, the following methods should be used, independently or in any combination, providing that the zones of protection afforded by different parts of the air-termination overlap and ensure that the structure is entirely protected according to 5.2:

• protection angle method;

• rolling sphere method;

• 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 positioning method may be selected by the LPS designer. However, the following considerations may be valid:

• the protection angle method is suitable for simple structures or for small parts of bigger structures. This method is not suitable for structures higher than the radius of the rolling sphere relevant to the selected protection level of the LPS;

• the rolling sphere method is suitable for complex shaped structures;

• the mesh method is for general purposes and it is particularly suitable for the protection of plane surfaces.

The air-termination design method and LPS design methods used for the various parts of the structure should be explicitly stated in the design documentation.

E.5.2.2.1 Protection angle method

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 a to the vertical in all directions.

The protection angle a should conform to Table 2, with h being the height of the air­termination above the surface to be protected.

A single point generates a cone. Figures A.1 and A.2 show how the protected space is generated by the different air-termination conductors in the LPS.

According to Table 2, the protection angle a is different for different heights of air-termination above the surface to be protected (see Figures A.3 and E.12).

Key

Н height of the building over the ground reference plane physical height of an air-termination rod