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The LPZs are implemented by the installation of the SPM, e.g. installation of a coordinated SPD system and/or magnetic shielding (see Figure 2). Depending on the number, type and withstand level of the equipment to be protected, suitable LPZ can be defined. These may include small local zones (e.g. equipment enclosures) or large integral zones (e.g. the whole structure) (see Figure B.2).

Interconnection of LPZs of the same order may be necessary if either two separate structures are connected by electrical or signal lines, or the number of required SPDs is to be reduced (see Figure 3).

NOTE Figure За shows two LPZ 1 connected by electrical or signal lines. Special care should be taken if both LPZ 1 represent separate structures with separate earthing systems, spaced tens or hundreds of metres from each other. In this case, a large part of the lightning current can flow along the connecting lines, which are not protected.

Key

/p l₂ partial lightning currents

Figure 3a - Interconnecting two LPZ 1 using SPDs

NOTE Figure 3b shows, that this problem can be solved using shielded cables or shielded cable ducts to interconnect both LPZ 1, provided that the shields are able to carry the partial lightning current. The SPD can be omitted, if the voltage drop along the shield is not too high.

Key

/р /₂ partial lightning currents

Figure 3b - Interconnecting two LPZ 1 using
shielded cables or shielded cable duct

s

ІЕС 2768/10

ІЕС 2769/10

NOTE Figure Зс shows two LPZ 2 connected by electrical or signal lines. Because the lines are exposed to the threat level of LPZ 1, SPDs at the entry into each LPZ 2 are required.

Figure 3c - Interconnecting two LPZ 2 using SPDs

NOTE Figure 3d shows that such interference can be avoided and the SPDs can be omitted, if shielded cables or shielded cable ducts are used to interconnect both LPZ 2.

Figure 3d - Interconnecting two LPZ 2 using
shielded cables or shielded cable ducts

3. - Examples for interconnected LPZ

Extending an LPZ into another LPZ might be needed in special cases or can be used to reduce the number of required SPDs (see Figure 4).

Detailed evaluation of the electromagnetic environment in an LPZ is described in Annex A.

IEC 2770/10

IEC 2771/10

NOTE Figure 4a shows a structure powered by a transformer. If the transformer is placed outside the structure, only the low voltage lines entering the structure require protection using an SPD.

NOTE If the transformer is placed inside the structure and does not have an SPD installed on the HV side (since the owner of the building is often not permitted to adopt protection measures on the high voltage side) then Figure 4b applies. Figure 4b shows that the problem can be solved by extending LPZ 0 into LPZ 1, which again requires SPDs to be installed on the low voltage side only.

Figure 4a - Transformer outside the structure

Figure 4b - Transformer inside the structure

Figure 4c - Two coordinated SPDs needed - SPD (between zones 0/1) and SPD (between zones 1/2)

NOTE Figure 4c shows an LPZ 2 supplied by an electrical or signal line. This line needs two coordinated SPDs: one at the boundary of LPZs 0/1, the other at the boundary of LPZs 1/2.

(within LPZ 0)

N

(LPZ 0 extended into LPZ 1)

OTE Figure 4d shows that the line can enter immediately into LPZ 2 and only one SPD is required, if LPZ 2 is extended into LPZ 1 using shielded cables or shielded cable ducts. However this SPD will reduce the threat immediately to the level of LPZ 2.

Figure 4d - Only one SPD needed -SPD (between zones 0/2)
(LPZ 2 extended into LPZ 1)

3. - Examples for extended lightning protection zones

4.4 Basic SPM

Basic protection measures against LEMP include:

• Earthing and bonding (see Clause 5)

The earthing system conducts and disperses the lightning current into the earth.

The bonding network minimizes potential differences and may reduce the magnetic field.

• Magnetic shielding and line routing (see Clause 6)

Spatial shielding attenuates the magnetic field inside the LPZ, arising from lightning flashes direct to or nearby the structure, and reduces internal surges.

Shielding of internal lines, using shielded cables or cable ducts, minimizes internally- induced surges.

Routing of internal lines can minimize induction loops and reduce internal surges.

NOTE 1 Spatial shielding, shielding and routing of internal lines can be combined or used separately.

Shielding of external lines entering the structure reduces surges from being conducted onto the internal systems.

• Coordinated SPD system (see Clause 7)

A coordinated SPD system limits the effects of externally originated and internally created surges.

• Isolating interfaces (see Clause 8)

Isolating interfaces limits the effects of conducted surges on lines entering the LPZ.

Earthing and bonding should always be ensured, in particular, bonding of every conductive service directly or via an equipotential bonding SPD, at the point of entry to the structure.Other SPM can be used alone or in combination.

SPM shall withstand the operational stresses expected in the installation place (e.g. stress of temperature, humidity, corrosive atmosphere, vibration, voltage and current).

Selection of the most suitable SPM shall be made using a risk assessment in accordance with IEC 62305-2, taking into account technical and economic factors.

Practical information on the implementation of SPM for internal systems in existing structures is given in Annex B.

NOTE 2 Lightning equipotential bonding (EB) in accordance with IEC 62305-3 will protect against dangerous sparking only. Protection of internal systems against surges requires a coordinated SPD system in accordance with this standard.

NOTE 3 Further information on the implementation of SPM can be found in IEC 60364-4-44.

5 Earthing and bonding

Suitable earthing and bonding are based on a complete earthing system (see Figure 5) combining

• the earth-termination system (dispersing the lightning current into the soil), and

the bonding network (minimizing potential differences and reducing the magnetic field)

.

/ЕС 2774/10

NOTE All drawn conductors are either bonded structural metal elements or bonding conductors. Some of them may also serve to intercept, conduct and disperse the lightning current into the earth.

Figure 5 - Example of a three-dimensional earthing system consisting of the bonding
network interconnected with the earth-termination system

The earth-termination system of the structure shall comply with IEC 62305-3. In structures where only electrical systems are provided, a type A earthing arrangement may be used, but a type В earthing arrangement is preferable. In structures with electronic systems, a type В

1. earthing arrangement is recommended.

■ The ring earth electrode around the structure, or the ring earth electrode in the concrete at the

, ► perimeter of the foundation, should be integrated with a meshed network under and around

і the structure, having a mesh width of typically 5 m. This greatly improves the performance of

і the earth-termination system. If the basement’s reinforced concrete floor forms a well defined

interconnected mesh and is connected to the earth-termination system, typically every 5 m, it is also suitable. An example of a meshed earth-termination system of a plant is shown in Figure 6.

Key

1. building with meshed network of the reinforcement

2. tower inside the plant

3. stand-alone equipment

4. cable tray

Figure 6 - Meshed earth-termination system of a plant

To reduce potential differences between two internal systems, which may be referenced in some special cases to separate earthing systems, the following methods may be applied:

• several parallel bonding conductors running in the same paths as the electrical cables, or the cables enclosed in grid-like reinforced concrete ducts (or continuously bonded metal conduit), which have been integrated into both of the earth-termination systems;

• shielded cables with shields of adequate cross-section, and bonded to the separate earthing systems at either end.

5.3 Bonding network

A low impedance bonding network is needed to avoid dangerous potential differences between all equipment inside the inner LPZ. Moreover, such a bonding network also reduces the magnetic field (see Annex A).

This can be realised by a meshed bonding network integrating conductive parts of the structure, or parts of the internal systems, and by bonding metal parts or conductive services at the boundary of each LPZ directly or by using suitable SPDs.

The bonding network can be arranged as a three-dimensional meshed structure with a typical mesh width of 5 m (see Figure 5). This requires multiple interconnections of metal components in and on the structure (such as concrete reinforcement, elevator rails, cranes, metal roofs, metal facades, metal frames of windows and doors, metal floor frames, service pipes and cable trays). Bonding bars (e.g. ring bonding bars, several bonding bars at different levels of the structure) and magnetic shields of the LPZ shall be integrated in the same way.

Examples of bonding networks are shown in Figures 7 and 8.

ІЕС 2776/10

Key

1. air-termination conductor

2. metal covering of the roof parapet

3. steel reinforcing rods

4. mesh conductors superimposed on the reinforcement

5. joint of the mesh conductor

6. joint for an internal bonding bar

7. connection made by welding or clamping

8. arbitrary connection

9. steel reinforcement in concrete (with superimposed mesh conductors)

10. ring earthing electrode (if any)

11 foundation earthing electrode

a typical distance of 5 m for superimposed mesh conductors

b typical distance of 1 m for connecting this mesh with the reinforcement

7. - Utilization of reinforcing rods of a structure for equipotential bonding

Key

1

2

З

4

5

6

7

8

9

IEC 2777/10

electrical power equipment

steel girder

metal covering of the facade

bonding joint

electrical or electronic equipment

bonding bar

steel reinforcement in concrete (with superimposed mesh conductors) foundation earthing electrode

common entry point for different services

- Equipotential bonding in a structure with steel reinforcementConductive parts (e.g. cabinets, enclosures, racks) and the protective earth conductor (PE) of the internal systems shall be connected to the bonding network in accordance with the following configurations (see Figure 9):

IEC 2778/10

Key

- bonding network

bonding conductor

I I equipment

• bonding point to the bonding network

ERP earthing reference point

Sg star point configuration integrated by star point

M_M meshed configuration integrated by mesh

Figure 9 - Integration of conductive parts of internal systems into the bonding network

If the configuration S is used, all metal components (e.g. cabinets, enclosures, racks) of the internal systems shall be isolated from the earthing system. The configuration S shall be integrated into the earthing system only by a single bonding bar acting as the earth reference point (ERP) resulting in type S_s. When configuration S is used, all lines between the individual equipment shall run in parallel with, and close to, the bonding conductors following the star configuration in order to avoid induction loops. Configuration S can be used where internal systems are located in relatively small zones and all lines enter the zone at one point only.

If configuration M is used, the metal components (e.g. cabinets, enclosures, racks) of the internal systems are not to be isolated from the earthing system, but shall be integrated into it by multiple bonding points, resulting in type M_M. Configuration M is preferred for internal systems extended over relatively wide zones or over a whole structure, where many lines run between the individual pieces of equipment, and where the lines enter the structure at several points.

In complex systems, the advantages of both configurations (configuration M and S) can be combined as illustrated in Figure 10, resulting in combination 1 (S_s combined with M_M) or in combination 2 (M_s combined with M_M).

Key

—— bonding network

bonding conductor

I I equipment

• bonding point to the bonding network

ERP earthing reference point

Sg star point configuration integrated by star point

meshed configuration integrated by mesh

Mg meshed configuration integrated by star point

Figure 10 - Combinations of integration methods of conductive parts of internal
systems into the bonding network

Bonding bars shall be installed for bonding of

• all conductive services entering an LPZ (directly or by using suitable SPDs),

• the protective earth conductor PE,

• metal components of the internal systems (e.g. cabinets, enclosures, racks),

• the magnetic shields of the LPZ at the periphery and inside the structure.

For efficient bonding the following installation rules are important:

• the basis for all bonding measures is a low impedance bonding network;

• bonding bars should be connected to the earthing system by the shortest possible route;

• material and dimensions of bonding bars and bonding conductors shall comply with 5.6;

• SPDs should be installed in such a way as to use the shortest possible connections to the bonding bar as well as to live conductors, thus minimizing inductive voltage drops;

• on the protected side of the circuit (downstream of an SPD), mutual induction effects should be minimized, either by minimizing the loop area or using shielded cables or cable ducts.

Where an LPZ is defined, bonding shall be provided for all metal parts and services (e.g. metal pipes, power lines or signal lines) penetrating the boundary of the LPZ.

NOTE Bonding of services entering LPZ 1 should be discussed with the service network providers involved (e.g. electrical power or telecommunication authorities), because there could be conflicting requirements.

Bonding shall be performed via bonding bars, which are installed as closely as possible to the entrance point at the boundary.

Where possible, incoming services should enter the LPZ at the same location and be connected to the same bonding bar. If services enter the LPZ at different locations, each service shall be connected to a bonding bar and these bonding bars shall be connected together. To realise this, bonding to a ring bonding bar (ring conductor) is recommended.

Equipotential bonding SPDs are always required at the entrance of the LPZ to bond incoming lines, which are connected to the internal systems within the LPZ, to the bonding bar. Using an interconnected or extended LPZ can reduce the number of SPDs required.

Shielded cables or interconnected metal cable ducts, bonded at each LPZ boundary, can be used either to interconnect several LPZ of the same order to one joint LPZ, or to extend an LPZ to the next boundary.

Material, dimensions and conditions of use shall comply with IEC 62305-3. The minimum cross-section for bonding components shall comply with Table 1 below.

Clamps shall be dimensioned in accordance with the lightning current values of the LPL (see IEC 62305-1) and the current sharing analysis (see IEC 62305-3).

SPDs shall be dimensioned in accordance with Clause 7.Table 1 - Minimum cross-sections for bonding components

6. Magnetic shielding and line routing

   1. General

Magnetic shielding can reduce the electromagnetic field as well as the magnitude of induced internal surges. Suitable routing of internal lines can also minimize the magnitude of induced internal surges. Both measures are effective in reducing permanent failure of internal systems.

Spatial shields define protected zones, which may cover the whole structure, a part of it, a single room or the equipment enclosure only. These may be grid-like, or continuous metal shields, or comprise the "natural components" of the structure itself (see IEC 62305-3).

Spatial shields are advisable where it is more practical and useful to protect a defined zone of the structure instead of several individual pieces of equipment. Spatial shields should be provided in the early planning stage of a new structure or a new internal system. Retrofitting to existing installations may result in higher costs and greater technical difficulties.

Shielding may be restricted to cabling and equipment of the system to be protected; metallic shield of cables, closed metallic cable ducts and metallic enclosures of equipment are used for this purpose.

Suitable routing of internal lines minimizes induction loops and reduces the creation of surge voltages internally in the structure. The loop area can be minimized by routing the cables close to natural components of the structure which have been earthed and/or by routing electrical and signal lines together.NOTE Some distance between power lines and unshielded signal lines may still be needed to avoid interference.

Shielding of external lines entering the structure includes cable shields, closed metallic cable ducts and concrete cable ducts with interconnected reinforcement steel. Shielding of external lines is helpful, but often not the responsibility of the SPM planner (since the owner of external lines is normally the network provider).

At the boundary of LPZ 0_A and LPZ 1, materials and dimensions of magnetic shields (e.g. grid-like spatial shields, cable shields and equipment enclosures) shall comply with the requirements of IEC 62305-3 for air-termination conductors and/or down-conductors. In particular:

• minimum thickness of sheet metal parts, metal ducts, piping and cable shields shall comply with Table 3 of IEC 62305-3:2010;

• layouts of grid-like spatial shields and the minimum cross-section of their conductors, shall comply with Table 6 of IEC 62305-3:2010.

The dimensions of magnetic shields not intended to carry lightning currents are not required to conform to Tables 3 and 6 of IEC 62305-3:2010:

• at the boundary of LPZs 1/2 or higher, provided that the separation distance 5 between magnetic shields and the LPS is fulfilled (see 6.3 of IEC 62305-3:2010),

• at the boundary of any LPZ, if the number of dangerous events N_D due to lightning flashes to the structure is negligible, i.e. N_D < 0,01 per year.