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5. Annex C dealing with SPD coordination is withdrawn and referred back to SC 37A.A new informative Annex D is introduced giving information on factors to be considered in the selection of SPDs.

The text of this standard is based on the following documents:

Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table.

This publication has been drafted, as closely as possible, in accordance with the ISO/IEC Directives, Part 2.

A list of all the parts in the IEC 62305 series, under the general title Protection against lightning, can be found on the IEC website.

The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to the specific publication. At this date, the publication will be

• reconfirmed,

• withdrawn,

• replaced by a revised edition, or

• amended.

A bilingual version of this standard may be issued at a later date

.INTRODUCTION

Lightning as a source of harm is a very high energy phenomenon. Lightning flashes release many hundreds of mega-joules of energy. When compared with the milli-joules of energy that may be sufficient to cause damage to sensitive electronic equipment in electrical and electronic systems within a structure, it is clear that additional protection measures will be necessary to protect some of this equipment.

The need for this International Standard has arisen due to the increasing cost of failures of electrical and electronic systems, caused by electromagnetic effects of lightning. Of particular importance are electronic systems used in data processing and storage as well as process control and safety for plants of considerable capital cost, size and complexity (for which plant outages are very undesirable for cost and safety reasons).

Lightning can cause different types of damage in a structure, as defined in IEC 62305-1:

D1 injury to living beings by electric shock;

D2 physical damage (fire, explosion, mechanical destruction, chemical release) due to lightning current effects, including sparking;

D3 failure of internal systems due to LEMP.

IEC 62305-3 deals with the protection measures to reduce the risk of physical damage and life hazard, but does not cover the protection of electrical and electronic systems.

This Part 4 of IEC 62305 therefore provides information on protection measures to reduce the risk of permanent failures of electrical and electronic systems within structures.

Permanent failure of electrical and electronic systems can be caused by the lightning electromagnetic impulse (LEMP) via:

1. conducted and induced surges transmitted to equipment via connecting wiring;

2. the effects of radiated electromagnetic fields directly into equipment itself.

Surges to the structure can originate from sources external to the structure or from within the structure itself:

• surges which originate externally from the structure are created by lightning flashes striking incoming lines or the nearby ground, and are transmitted to electrical and electronic systems within the structure via these lines;

• surges which originate internally within the structure are created by lightning flashes striking the structure itself or the nearby ground.

NOTE 1 Surges can also originate internally within the structure, from switching effects, e.g. switching of inductive loads.

The coupling can arise from different mechanisms:

• resistive coupling (e.g. the earth impedance of the earth-termination system or the cable shield resistance);

• magnetic field coupling (e.g. caused by wiring loops in the electrical and electronic system or by inductance of bonding conductors);

• electric field coupling (e.g. caused by rod antenna reception).

NOTE 2 The effects of electric field coupling are generally very small when compared to the magnetic field coupling and can be disregarded.

Radiated electromagnetic fields can be generated via

• the direct lightning current flowing in the lightning channel,

the partial lightning current flowing in conductors (e.g. in the down-conductors of an external LPS in accordance with IEC 62305-3 or in an external spatial shield in accordance with this standard).PROTECTION AGAINST LIGHTNING -

Part 4: Electrical and electronic systems within structures

1. Scope

This part of IEC 62305 provides information for the design, installation, inspection, maintenance and testing of electrical and electronic system protection (SPM) to reduce the risk of permanent failures due to lightning electromagnetic impulse (LEMP) within a structure.

This standard does not cover protection against electromagnetic interference due to lightning, which may cause malfunctioning of internal systems. However, the information reported in Annex A can also be used to evaluate such disturbances. Protection measures against electromagnetic interference are covered in IEC 60364-4-44 ^{[1] 1} and in the IEC 61000 series [2]

This standard provides guidelines for cooperation between the designer of the electrical and electronic system, and the designer of the protection measures, in an attempt to achieve optimum protection effectiveness.

This standard does not deal with detailed design of the electrical and electronic systems themselves.

2. Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

IEC 60364-5-53:2001, Electrical installations of buildings - Part 5-53: Selection and erection of electrical equipment - Isolation, switching and control

IEC 60664-1:2007, Insulation coordination for equipment within low-voltage systems - Part 1: Principles, requirements and tests

IEC 61000-4-5:2005, Electromagnetic compatibility (EMC) - Part 4-5: Testing and measure­ment techniques - Surge immunity test

IEC 61000-4-9:1993, Electromagnetic compatibility (EMC) - Part 4-9: Testing and measure­ment techniques - Pulse magnetic field immunity test - Basic EMC Publication

IEC 61000-4-10:1993, Electromagnetic compatibility (EMC) - Part 4-10: Testing and measure­ment techniques - Damped oscillatory magnetic field immunity test - Basic EMC Publication

IEC 61643-1:2005, Low-voltage surge protective devices - Part 1: Surge protective devices connected to low-voltage power distribution systems - Requirements and tests

IEC 61643-12:2008, Low-voltage surge protective devices - Part 12: Surge protective devices connected to low-voltage power distribution systems - Selection and application principles

ІЕС 61643-21, Low voltage surge protective devices - Part 21: Surge protective devices connected to telecommunications and signalling networks - Performance requirements and testing methods

I EC 61643-22, Low voltage surge protective devices - Part 22: Surge protective devices connected to telecommunications and signalling networks - Selection and application principles

IEC 62305-1:2010, Protection against lightning - Part 1: General principles

IEC 62305-2:2010, Protection against lightning - Part 2: Risk management

IEC 62305-3:2010, Protection against lightning - Part 3: Physical damage to structures and life hazard

3. Terms and definitions

For the purposes of this document, the following terms and definitions, as well as those given in other parts of IEC 62305, apply.

electrical system

system incorporating low voltage power supply components

electronic system

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

internal systems

electrical and electronic systems within a structure

lightning protection

LP

complete system for the protection of structures and/or electrical and electronic systems in those structures from the effects of lightning, consisting of an LPS and SPM

lightning protection system

LPS

complete system used to reduce physical damage due to lightning flashes to a structure

NOTE It consists of both external and internal lightning protection systems.

lightning electromagnetic impulse

LEMP

all electromagnetic effects of lightning current via resistive, inductive and capacitive coupling which create surges and electromagnetic fields

surge

rated impulse withstand voltage level

impulse withstand voltage assigned by the manufacturer to the equipment or to a part of it, characterizing the specified withstand capability of its insulation against overvoltages

NOTE For the purposes of this part of IEC 62305, only withstand voltage between live conductors and earth is considered.

lightning protection level

LPL

number related to a set of lightning current parameters relevant to the probability that the associated maximum and minimum design values will not be exceeded in naturally occurring lightning

NOTE Lightning protection level is used to design protection measures according to the relevant set of lightning current parameters.

3.10

lightning protection zone

LPZ

zone where the lightning electromagnetic environment is defined

NOTE The zone boundaries of an LPZ are not necessarily physical boundaries (e.g. walls, floor and ceiling).

3.11

LEMP protection measures

SPM

measures taken to protect internal systems against the effects of LEMP

NOTE This is part of overall lightning protection.

3.12

grid-like spatial shield

magnetic shield characterized by openings

NOTE For a building or a room, it is preferably built by interconnected natural metal components of the structure (e.g. rods of reinforcement in concrete, metal frames and metal supports).

3.13

earth-termination system

part of an external LPS which is intended to conduct and disperse lightning current into the earth

3.14

bonding network

interconnecting network of all conductive parts of the structure and of internal systems (live conductors excluded) to the earth-termination system

3.15

earthing system

complete system combining the earth-termination system and the bonding network

3.16

surge protective device

SPD

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

3.17

SPD tested with /_imp

SPDs which withstand the partial lightning current with a typical waveform 10/350 ps and require a corresponding impulse test current /_irnp

NOTE For power lines, a suitable test current /j_mp is defined in the Class I test procedure of IEC 61643-1:2005.

3.18

SPD tested with /_n

SPDs which withstand induced surge currents with a typical waveform 8/20 ps and require a corresponding impulse test current /_n

NOTE For power lines a suitable test current /_n is defined in the Class II test procedure of IEC 61643-1:2005.

3.19

SPD tested with a combination wave

SPDs that withstand induced surge currents with a typical waveform 8/20 ps and require a corresponding impulse test current /_sc

NOTE For power lines a suitable combination wave test is defined in the Class III test procedure of IEC 61643-1:2005 defining the open circuit voltage U_QC 1,2/50 ps and the short-circuit current /_sc 8/20 ps of a 2 Cl combination wave generator.

3.20

voltage-switching type SPD

SPD that has a high impedance when no surge is present, but can have a sudden change in impedance to a low value in response to a voltage surge

NOTE 1 Common examples of components used as voltage switching devices include spark gaps, gas discharge tubes (GDT), thyristors (silicon controlled rectifiers) and triacs. These SPDs are sometimes called "crowbar type".

NOTE 2 A voltage-switching device has a discontinuous voltage/current characteristic.

3.21

voltage-limiting type SPD

SPD that has a high impedance when no surge is present, but will reduce it continuously with increased surge current and voltage

NOTE 1 Common examples of components used as non-linear devices are varistors and suppressor diodes. These SPDs are sometimes called "clamping type".

NOTE 2 A voltage-limiting device has a continuous voltage/current characteristic.

3.22

combination type SPD

SPD that incorporates both voltage-switching and voltage-limiting type components and that may exhibit voltage-switching, voltage-limiting or both voltage-switching and voltage-limiting behaviour, depending upon the characteristics of the applied voltage

3.23

coordinated SPD system

SPDs properly selected, coordinated and installed to form a system intended to reduce failures of electrical and electronic systems

3.24

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. Design and installation of SPM

   1. General

Electrical and electronic systems are subject to damage from a lightning electromagnetic impulse (LEMP). Therefore SPM need to be provided to avoid failure of internal systems.

The design of SPM should be carried out by experts in lightning and surge protection who possess a broad knowledge of EMC and installation practices.

Protection against LEMP is based on the lightning protection zone (LPZ) concept: the zone containing systems to be protected shall be divided into LPZs. These zones are theoretically assigned part of space (or of an internal system) where the LEMP severity is compatible with the withstand level of the internal systems enclosed (see Figure 1). Successive zones are characterized by significant changes in the LEMP severity. The boundary of an LPZ is defined by the protection measures employed (see Figure 2).

IEC 2762/Г0

Bonding of incoming services directly or by suitable SPD

NOTE This figure shows an example of dividing a structure into inner LPZs. All metal services entering the structure are bonded via bonding bars at the boundary of LPZ 1. In addition, the conductive services entering LPZ 2 (e.g. computer room) are bonded via bonding bars at the boundary of LPZ 2.

Figure 1 - General principle for the division into different LPZ

ІЕС 2763/10

Figure 2а - SPM using spatial shields and a coordinated SPD system - Equipment well protected against conducted surges (U₂«U₀ and /₂«/_Q) and against radiated magnetic fields (H₂«H₀)

IEC 2764/10

Figure 2b - SPM using spatial shield of LPZ 1 and SPD protection at entry of LPZ 1 - Equipment protected against conducted surges (U^<Uq and and against radiated magnetic fields

Figure 2с - SPM using internal line shielding and SPD protection at entry of LPZ 1 - Equipment protected against conducted surges (U₂<Uq and /₂</q) and against radiated magnetic fields (W2<Hq)

Figure 2d - SPM using a coordinated SPD system only -Equipment protected against conducted surges (U₂«U_oand l₂«lg), but not against radiated magnetic field (Wq)

Key shielded boundary non-shielded boundary

NOTE 1 SPDs can be located at the following points:

• at the boundary of LPZ 1 (e.g. at main distribution board MB);

• at the boundary of LPZ 2 (e.g. at secondary distribution board SB);

• at or close to equipment (e.g. at socket outlet SA).

NOTE 2 For detailed installation rules see also IEC 60364-5-53.

Figure 2 - Examples of possible SPM (LEMP protection measures)

Permanent failure of electrical and electronic systems due to LEMP can be caused by • conducted and induced surges transmitted to equipment via connecting wiring, • effects of radiated electromagnetic fields impinging directly onto equipment itself.

For protection against the effects of radiated electromagnetic fields impinging directly onto the equipment, SPM consisting of spatial shields and/or shielded lines, combined with shielded equipment enclosures, should be used.

For protection against the effects of conducted and induced surges being transmitted to the equipment via connection wiring, SPM consisting of a coordinated SPD system should be used.

Failures due to electromagnetic fields impinging directly onto the equipment can be considered negligible provided the equipment complies with the relevant radio frequency emission and immunity EMC product standards.

In general, equipment is required to comply with the relevant EMC product standards therefore SPM consisting of a coordinated SPD system is usually considered sufficient to protect such equipment against the effects of LEMP.

For equipment not complying with relevant EMC product standards, SPM consisting of a coordinated SPD system alone is considered inadequate to protect such equipment against the effects of LEMP. In this case, Annex A provides further information as to how to achieve best protection against directly impinging electromagnetic fields. The equipment’s withstand level against radiated magnetic fields needs to be selected in accordance with IEC 61000-4-9 and IEC 61000-4-10.

If required for specific applications, a simulated system-level test which includes the SPD(s), installation wiring and the actual equipment may be performed in the laboratory to verify protection withstand coordination.

SPM can be designed for protection of equipment against surges and electromagnetic fields. Figure 2 provides some examples of SPM using protection measures, such as LPS, magnetic shields and coordinated SPD systems:

• SPM employing spatial shields and a coordinated SPD system will protect against radiated magnetic fields and against conducted surges (see Figure 2a). Cascaded spatial shields and coordinated SPDs can reduce the magnetic field and surges to a lower threat level.

• SPM employing a spatial shield of LPZ 1 and an SPD at the entry of LPZ 1 can protect equipment against the radiated magnetic field and against conducted surges (see Figure 2b).

NOTE 1 The protection would not be sufficient if the magnetic field remains too high (due to low shielding effectiveness of LPZ 1), or if the surge magnitude remains too high (due to a high voltage protection level of the SPD and due to the induction effects onto wiring downstream of the SPD).

• SPM using shielded lines, combined with shielded equipment enclosures, will protect against radiated magnetic fields. The SPD at the entry of LPZ 1 will provide protection against conducted surges (see Figure 2c). To achieve a lower threat level (in one step from LPZ 0 to LPZ 2), a special SPD may be required (e.g. additional coordinated stages inside) to reach a sufficient low voltage protection level.

• SPM using a coordinated SPD system is only suitable to protect equipment which is insensitive to radiated magnetic fields, since the SPDs will only provide protection against conducted surges (see Figure 2d). A lower threat surge level can be achieved using coordinated SPDs.

NOTE 2 Solutions in accordance with Figures 2a to 2c are recommended especially for equipment which does not comply with relevant EMC product standards.

NOTE 3 An LPS in accordance with IEC 62305-3 that employs only equipotential bonding SPDs provides no effective protection against failure of sensitive electrical and electronic systems. The LPS can be improved by reducing the mesh dimensions and selecting suitable SPDs, so as to make it an effective component of the SPM.

With respect to lightning threat, the following LPZ are defined (see IEC 62305-1):

Outer zones:

LPZ 0 Zone where the threat is due to the unattenuated lightning electromagnetic field and where the internal systems may be subjected to full or partial lightning surge current. LPZ 0 is subdivided into:

LPZ 0_A zone where the threat is due to the direct lightning flash and the full lightning electromagnetic field. The internal systems may be subjected to full lightning surge current.

LPZ 0_B zone protected against direct lightning flashes but where the threat is the full lightning electromagnetic field. The internal systems may be subjected to partial lightning surge currents.

Inner zones: (protected against direct lightning flashes)

LPZ 1 Zone where the surge current is limited by current sharing and isolating interfaces and/or by SPDs at the boundary. Spatial shielding may attenuate the lightning electromagnetic field.

LPZ 2...n Zone where the surge current may be further limited by current sharing and isolating interfaces and/or and by additional SPDs at the boundary. Additional spatial shielding may be used to further attenuate the lightning electromagnetic field.