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3.16

connecting component

part of an LPS which is used for the connection of conductors to each other or to metallic installations

NOTE This also includes bridging component and expansion piece.

3.17

fixing component

part of an LPS which is used to fix the elements of the LPS to the structure to be protected

3.18

metal installations

extended metal items in the structure to be protected which may form a path for lightning current, such as pipework, staircases, elevator guide rails, ventilation, heating and air­conditioning ducts, interconnected reinforcing steel, structural metal parts

3.19

external conductive parts

extended metal items entering or leaving the structure to be protected such as pipework, metallic cable elements, metal ducts, etc. which may carry a part of the lightning current

3.20

electrical system

system incorporating low-voltage power supply components

3.21

electronic system

system incorporating sensitive electronic components such as telecommunication equipment, computer, control and instrumentation systems, radio systems, power electronic installations

3.22

internal systems

electrical and electronic systems within a structure

3.23

lightning equipotential bonding

EB

bonding to the LPS of separated conductive parts, by direct connections or via surge protective devices, to reduce potential differences caused by lightning current

3.24

bonding bar

metal bar on which metal installations, external conductive parts, electric power and tele­communication lines and other cables can be bonded to an LPS

3.25

bonding conductor

conductor connecting separated conductive parts to LPS

3.26

interconnected reinforcing steel

steelwork within a concrete structure which is considered electrically continuous

3.27

dangerous sparking

electrical discharge due to lightning which causes physical damage in the structure to be protected

3.28

separation distance

distance between two conductive parts at which no dangerous sparking can occur

3.29

surge protective device

SPD

device intended to limit transient overvoltages and divert surge currents; contains at least one non linear component

3.30

test joint

joint designed to facilitate electrical testing and measurement of LPS components

3.31

class of LPS

number denoting the classification of an LPS according to the lightning protection level for which it is designed

3.32

lightning protection designer

specialist competent and skilled in the design of the LPS

3.33

lightning protection installer

person competent and skilled in the installation of the LPS

3.34

structures with risk of explosion

structures containing solid explosives materials or hazardous zones as determined in accordance with IEC 60079-10-1 and IEC 60079-10-2

3.35

isolating spark gap

ISG

component with discharge distance for isolating electrically conductive installation sections

NOTE In the event of a lightning strike, the installation sections are temporarily connected conductively as the result of response to the discharge.

3.36

isolating interfaces

devices which are capable of reducing conducted surges on lines entering the LPZ

NOTE 1 These include isolation transformers with earthed screen between windings, metal-free fibre optic cables and opto-isolators.

NOTE 2 Insulation withstand characteristics of these devices are suitable for this application intrinsically or via SPD.

4. Lightning protection system (LPS)

   1. Class of LPS

The characteristics of an LPS are determined by the characteristics of the structure to be protected and by the considered lightning protection level.

Four classes of LPS (I to IV), as shown in Table 1, are defined in this standard corresponding to lightning protection levels defined in IEC 62305-1.

Table 1 - Relation between lightning protection levels (LPL) and class of LPS (see IEC 62305-1)

Each class of LPS is characterized by the following:

1. Data dependent upon the class of LPS:

• lightning parameters (see Tables 3 and 4 in IEC 62305-1:2010);

• rolling sphere radius, mesh size and protection angle (see 5.2.2);

• typical preferred distances between down-conductors (see 5.3.3);

• separation distance against dangerous sparking (see 6.3);

• minimum length of earth electrodes (see 5.4.2).

2. Factors not dependent upon the class of LPS:

• lightning equipotential bonding (see 6.2);

• minimum thickness of metal sheets or metal pipes in air-termination systems (see 5.2.5);

• LPS materials and conditions of use (see 5.5.1);

• material, configuration and minimum dimensions for air-terminations, down-conductors and earth-terminations (see 5.6);

• minimum dimensions of connecting conductors (see 6.2.2).

Performance of each class of LPS is given in Annex В of IEC 62305-2:2010.

The class of required LPS shall be selected on the basis of a risk assessment (see IEC 62305-2).

A technically and economically optimized design of an LPS is possible, especially if the steps in the design and construction of the LPS are coordinated with the steps in the design and construction of the structure to be protected. In particular, the design of the structure itself should utilize the metal parts of the structure as parts of the LPS.

The design of the class and location of the LPS for existing structures shall take into account the constraints of the existing situation.

The design documentation of an LPS shall contain all the information necessary to ensure correct and complete installation. For detailed information, see Annex E.

The LPS should be designed and installed by well-trained and expert LPS designers and installers (see E.4.2)

Steelwork within reinforced concrete structures is considered to be electrically continuous provided that the major part of interconnections of vertical and horizontal bars are welded or otherwise securely connected. Connections of vertical bars shall be welded, clamped or overlapped a minimum of 20 times their diameters and bound or otherwise securely connected (see Figure E.5). For new structures, the connections between reinforcement elements shall be specified by the designer or installer, in cooperation with the builder and the civil engineer.

For structures utilizing steel-reinforced concrete (including pre-cast, pre-stressed reinforced units), the electrical continuity of the reinforcing bars shall be determined by electrical testing between the uppermost part and ground level. The overall electrical resistance should not be greater than 0,2 Q, measured using test equipment suitable for this purpose. If this value is not achieved, or it is not practical to conduct such testing, the reinforcing steel shall not be used as a natural down-conductor as discussed in 5.3.5. In this case it is recommended that an external down-conductor system be installed. In the case of structures of pre-cast reinforced concrete, the electrical continuity of the reinforcing steel shall be established between individual adjacent pre-cast concrete units.

NOTE 1 For further information on the continuity of steelwork in reinforced concrete structures, see Annex E.

NOTE 2 In several countries, the use of reinforced concrete as a part of the LPS is not allowed.

NOTE 3 Clamps to establish the continuity of steelwork in reinforced concrete should comply with the future IEC 62561-1.

4. External lightning protection system

   1. General

      1. Application of an external LPS

The external LPS is intended to intercept direct lightning flashes to the structure, including flashes to the side of the structure, and conduct the lightning current from the point of strike to ground. The external LPS is also intended to disperse this current into the earth without causing thermal or mechanical damage, or dangerous sparking which may trigger fire or explosions.

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

An isolated external LPS should be considered when the thermal and explosive effects at the point of strike, or on the conductors carrying the lightning current, may cause damage to the structure or to the contents (see Annex E). Typical examples include structures with combustible covering, structures with combustible walls and areas at risk of explosion and fire.

NOTE The use of an isolated LPS may be convenient where it is predicted that changes in the structure, its contents or its use will require modifications to the LPS.

An isolated external LPS may also be considered when the susceptibility of the contents warrants the reduction of the radiated electromagnetic field associated with the lightning current pulse in the down-conductor.

Natural components made of conductive materials, which will always remain in/on the structure and will not be modified (e.g. interconnected steel-reinforcement, metal framework of the structure, etc.) may be used as parts of an LPS.

Other natural components can only be considered as being additional to an LPS.

NOTE For further information, see Annex E.

The probability of structure penetration by a lightning current is considerably decreased by the presence of a properly designed air-termination system.

Air-termination systems can be composed of any combination of the following elements:

1. rods (including free-standing masts);

2. catenary wires;

3. meshed conductors.

To conform to this standard, all types of air-termination systems shall be positioned in accordance with 5.2.2, 5.2.3 and Annex A. All types of air terminals shall comply in full with this standard.

For all types of air terminals only the real physical dimensions of the metal air-termination systems shall be used for the determination of the volume protected.

The individual air-termination rods should be connected together at roof level to ensure current division.

Radioactive air terminals are not allowed.

Air-termination components installed on a structure shall be located at corners, exposed points and edges (especially on the upper level of any facades) in accordance with one or more of the following methods.

Acceptable methods to be used in determining the position of the air-termination system include:

• the protection angle method;

• the rolling sphere method;

• the mesh method.

The rolling sphere method is suitable in all cases.

The protection angle method is suitable for simple-shaped buildings but it is subject to limits of air-termination height indicated in Table 2.

The mesh method is a suitable form of protection where plane surfaces are to be protected.

The values for the protection angle, rolling sphere radius and mesh size for each class of LPS are given in Table 2 and Figure 1. Detailed information on the positioning of the air­termination system is given in Annex A

.

Table 2 - Maximum values of rolling sphere radius, mesh size and protection angle corresponding to the class of LPS

NOTE 1 Not applicable beyond the values marked with •. Only rolling sphere and mesh methods apply in these cases.

NOTE 2 ft is the height of air-termination above the reference plane of the area to be protected.

NOTE 3 The angle will not change for values of h below 2 m.

Figure 1 - Protection angle corresponding to the class of LPS

Research indicates that the probability of low amplitude strikes to the vertical side of a structure of less than 60 m in height are low enough that they need not be considered. Roofs and horizontal protrusions shall be protected in accordance with the class of LPS determined by the risk calculations of IEC 62305-2.

On structures taller than 60 m, flashes to the side may occur, especially to points, corners and edges of surfaces.NOTE 1 In general the risk due to these flashes is low because only a few per cent of all flashes to tall structures will be to the side and moreover their parameters are significantly lower than those of flashes to the top of structures. However, electrical and electronic equipment on walls outside structures may be destroyed even by lightning flashes with low current peak values.

An air-termination system shall be installed to protect the upper part of tall structures (i.e. typically the topmost 20 % of the height of the structure as far as this part exceeds 60 m in height) and the equipment installed on it (see Annex A).

The rules for positioning the air-termination systems on these upper parts of a structure shall meet at least the requirements for LPL IV with emphasis on the location of air-termination devices on corners, edges, and significant protrusions (such as balconies, viewing platforms, etc.).

The air-termination requirement for the side of a tall structure may be satisfied by the presence of external metallic materials such as metal cladding or metallic curtain walls provided they meet the minimum size requirements of Table 3. The air-termination requirement may also include the use of external down-conductors located on the vertical edges of the structure when not provided by natural external metallic conductors.

The installed or naturally occurring air-terminations meeting these requirements may utilize installed down-conductors or be suitably interconnected with natural down-conductors such as the steel frame of the structure or the metal of electrically-continuous reinforced concrete meeting the requirements of 5.3.5.

NOTE 2 Use of suitable earth-termination and natural down-conductors is encouraged.

Air-terminations of an LPS not isolated from the structure to be protected may be installed as follows:

• if the roof is made of non-combustible material the air-termination conductors may be positioned on the surface of the roof;

• if the roof is made of readily-combustible material, due care needs to be taken with regard to the distance between the air-termination conductors and the material. For thatched roofs, where no steel bars are used for mounting of the reed, a distance of at least 0,15 m is adequate. For other combustible materials a distance not lower than 0,10 m is considered adequate;

• easily-combustible parts of the structure to be protected shall not remain in direct contact with the components of an external LPS and shall not remain directly under any metallic roofing membrane that might be punctured by a lightning flash (see 5.2.5).

Account shall also be taken of less combustible membranes such as wooden sheets.

NOTE If it is likely that water may accumulate on a flat roof, air-terminations should be installed above the highest probable water level.

The following parts of a structure should be considered and may be used as natural air­termination components and part of an LPS in accordance with 5.1.3.

1. Metal sheets covering the structure to be protected provided that

• the electrical continuity between the various parts is made durable (e.g. by means of brazing, welding, crimping, seaming, screwing or bolting),

• the thickness of the metal sheet is not less than the value t’ given in Table 3 if it is not important to prevent puncture of the sheeting or to consider ignition of any readily- combustible materials underneath,

• the thickness of the metal sheet is not less than the value t given in Table 3 if it is necessary to take precautions against puncture or to consider hot spot problems,

NOTE 1 Where hot spot or ignition problems may arise, it should be verified that the temperature rise of the inner surface at the point of strike does not constitute a danger. Hot spot or ignition problems can be disregarded when the metal sheets lies inside an LPZOg or higher.

• they are not clad with insulating material.

Table 3 - Minimum thickness of metal sheets or metal pipes in air-termination systems

t prevents puncture.

t‘ only for metal sheets if it is not important to prevent puncture, hot spot or ignition problems.

2. Metal components of roof construction (trusses, interconnected reinforcing steel, etc.), underneath non-metallic roofing, provided that damage to this non-metallic roofing is acceptable.

3. Metal parts such as ornamentation, railings, pipes, coverings of parapets, etc., with cross­sections not less than that specified for standard air-termination components.

4. Metal pipes and tanks on the roof, provided that they are constructed of material with thicknesses and cross-sections in accordance with Table 6.

5. Metal pipes and tanks carrying readily-combustible or explosive mixtures, provided that they are constructed of material with thickness not less than the appropriate value of t given in Table 3 and that the temperature rise of the inner surface at the point of strike does not constitute a danger (for detailed information, see Annex D).

If the conditions for thickness are not fulfilled, the pipes and tanks shall be included into the structure to be protected.

Piping carrying readily-combustible or explosive mixtures shall not be considered as an air­termination natural component if the gasket in the flange couplings is not metallic or if the flange-sides are not otherwise properly bonded.

NOTE 2 A thin coating of protective paint or about 1 mm asphalt or 0,5 mm PVC is not regarded as an insulator. Detailed information is given in E.5.3.4.1 and in E.5.3.4.2.

5.3 Down-conductor systems

In order to reduce the probability of damage due to lightning current flowing in the LPS, the down-conductors shall be arranged in such a way that from the point of strike to earth:

1. several parallel current paths exist;

2. the length of the current paths is kept to a minimum;

3. equipotential bonding to conducting parts of the structure is performed according to the requirements of 6.2.

NOTE 1 Lateral connection of down-conductors is considered to be good practice.

The geometry of the down-conductors and of the ring conductors affects the separation distance (see 6.3).

NOTE 2 The installation of as many down-conductors as possible, at equal spacing around the perimeter interconnected by ring conductors, reduces the probability of dangerous sparking and facilitates the protection of internal installations (see IEC 62305-4). This condition is fulfilled in metal framework structures and in reinforced concrete structures in which the interconnected steel is electrically continuous.

Typical values of the preferred distance between down-conductors are given in Table 4.

More information on partitioning of the lightning current amongst down-conductors is given in Annex C.