IEC 62305-2:2006

IEC 62305-2
Edition 1.0 2006-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Protection against lightning –
Part 2: Risk management
Protection contre la foudre –
Partie 2: Evaluation des risques

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IEC 62305-2
Edition 1.0 2006-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Protection against lightning –
Part 2: Risk management
Protection contre la foudre –
Partie 2: Evaluation des risques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XE
CODE PRIX
ICS 29.020; 91.120.40 ISBN 2-8318-8364-4

62305-2  IEC:2006 –– 2 – 3 – 62305-2 © IEC:2006

CONTENTS
FOREWORD.7

INTRODUCTION.9

1 Scope.11

2 Normative references .11

3 Terms, definitions, symbols and abbreviations.11
4 Explanation of terms.21
4.1 Damage and loss .21
4.2 Risk and risk components.23
4.3 Composition of risk components related to a structure.25
4.4 Composition of risk components related to a service .27
4.5 Factors influencing the risk components.28
5 Risk management.29
5.1 Basic procedure .29
5.2 Structure to be considered for risk assessment .29
5.3 Service to be considered for risk assessment .29
5.4 Tolerable risk R .30
T
5.5 Specific procedure to evaluate the need of protection.30
5.6 Procedure to evaluate the cost effectiveness of protection .31
5.7 Protection measures .33
5.8 Selection of protection measures.33
6 Assessment of risk components for a structure.36
6.1 Basic equation.36
6.2 Assessment of risk components due to flashes to the structure (S1).36
6.3 Assessment of the risk component due to flashes near the structure (S2) .36
6.4 Assessment of risk components due to flashes to a line connected to the
structure (S3) .37
6.5 Assessment of risk component due to flashes near a line connected to the
structure (S4) .37
6.6 Summary of risk components in a structure .39

6.7 Partitioning of a structure in zones Z .39
S
6.8 Assessment of risk components in a structure with zones Z .40
S
7 Assessment of risk components for a service .41
7.1 Basic equation.41
7.2 Assessment of components due to flashes to the service (S3).41
7.3 Assessment of risk component due to flashes near the service (S4) .41
7.4 Assessment of risk components due to flashes to structures to which the
service is connected (S1) .42
7.5 Summary of risk components for a service .42
7.6 Partitioning of a service into sections S .43
S
62305-2 © IEC:200662305-2  IEC:2006 –– 3 – 5 –

Annex A (informative) Assessment of annual number N of dangerous events.44

Annex B (informative) Assessment of probability P of damage for a structure.53

X
Annex C (informative) Assessment of amount of loss L in a structure.59
X
Annex D (informative) Assessment of probability P′ of damage to a service .64
X
Annex E (informative) Assessment of the amount of loss L′ in a service.68

X
Annex F (informative) Switching overvoltages.70

Annex G (informative) Evaluation of costs of loss .71

Annex H (informative) Case study for structures .72

Annex I (informative) Case study for services – Telecommunication line.99
Annex J (informative)  Simplified software for risk assessment for structures.105

Bibliography.110

Figure 1 – Procedure for deciding the need of protection .31
Figure 2 – Procedure for evaluating the cost-effectiveness of protection measures.32
Fiigure 3 – Procedure for selecting protection measures in structures.34
Figure 4 – Procedure for selecting protection measures in services .35
Figure 5 – Structures at line ends: at “b” end the structure to be protected (structure b)
and at “a” end an adjacent structure(structure a) .38
Figure A.1 – Collection area A of an isolated structure .45
d
Figure A.2 – Complex shape structure .46
Figure A.3 – Different methods to determine the collection area for the structure of
Figure A.2.47
Figure A.4 – Structure to be considered for evaluation of collection area A .48
d
Figure A.5 – Collection areas (A , A , A , A ) .52
d m i l
Figure I.1 – Telecommunication line to be protected .99
Figure J.1 – Example for a country house (see Clause H.1 – no protection measures
provided) .108
Figure J.2 – Example for a country house (see Clause H.1 – protection measures
provided) .109

Table 1 – Sources of damage, types of damage and types of loss selected according
to the point of strike .22
Table 2 – Risk in a structure for each type of damage and of loss.23
Table 3 – Risk components to be considered for each type of loss in a structure .26
Table 4 – Risk components to be considered for each type of loss in a service.27
Table 5 – Factors influencing the risk components in a structure .28
Table 6 – Factors influencing the risk components in a service .29
Table 7 – Typical values of tolerable risk R .30
T
Table 8 – Parameters relevant to the assessment of risk components for a structure.38
Table 9 – Risk components for a structure for different types of damage caused by
different sources .39

62305-2  IEC:2006 –– 4 – 7 – 62305-2 © IEC:2006

Table 10 – Parameters relevant to the assessment of risk components for a service.42

Table 11 – Risk components for a service for different types of damage caused by

different sources .43

Table A. 1 – Values of collection area depending on the evaluation method.46

Table A.2 – Location factor C .49
d
Table A.3 – Collection areas A and A depending on the service characteristics.50
l i
Table A.4 – Transformer factor C .51
t
Table A.5 – Environmental factor C .51
e
Table B.1 – Values of probability P that a flash to a structure will cause shock to
A
living beings due to dangerous touch and step voltages.53
Table B.2 – Values of P depending on the protection measures to reduce physical
B
damage .54
Table B.3 – Value of the probability P as a function of LPL for which SPDs are
SPD
designed.54
Table B.4 – Value of the probability P as a function of factor K .55
MS MS
Table B.5 – Value of factor K depending on internal wiring .56
S3
Table B.6 – Values of the probability P depending on the resistance R of the cable
LD S
screen and the impulse withstand voltage U of the equipment .57
w
Table B.7 – Values of the probability P depending on the resistance R of the cable
LI S
screen and the impulse withstand voltage U of the equipment .58
w
Table C.1 – Typical mean values of L , L and L .60
t f o
Table C.2 – Values of reduction factors r and r as a function of the type of surface of
a u
soil or floor .60
Table C.3 – Values of reduction factor r as a function of provisions taken to reduce
p
the consequences of fire.61
Table C.4 – Values of reduction factor r as a function of risk of fire of structure .61
f
Table C.5 – Values of factor h increasing the relative amount of loss in presence of a
special hazard .61
Table C.6 – Typical mean values of L and L .62
f o
Table C.7 – Typical mean values of L , L and L .63
t f o
Table D.1 – Values of factor K as function of the characteristics of the shielded line .64
d
Table D.2 – Values of the factor K as function of the protection measures.65
p
Table D.3 – Impulse withstand voltage U as a function of the type of cable.65
w
Table D.4 – Impulse withstand voltage U as a function of the type of apparatus.65

w
Table D.5 – Values of probability P′ , P′ , P′ and P′ as function of the failure
B C V W
current I .66
a
Table E.1 – Typical mean values of L′ and L′ .68
f o
Table H.1 – Structure data and characteristics.72
Table H.2 – Data and characteristics of lines and connected internal systems .73
Table H.3 – Zone Z (inside the building) characteristics .74
Table H.4 – Collection areas of structure and lines .74
Table H.5 – Expected annual number of dangerous events.75
–5
Table H.6 – Risk components involved and their calculation (values x 10 ) .75

62305-2 © IEC:200662305-2  IEC:2006 –– 5 – 9 –

–5
Table H.7 – Values of risk components relevant to risk R (values × 10 ) for suitable
cases.77

Table H.8 – Structure characteristics .77

Table H.9 – Internal power system and connected power line characteristics.78

Table H.10 – Internal telecom system and connected TLC line characteristics .78

Table H.11 – Zone Z (entrance area to the building) characteristics .79
Table H.12 – Zone Z (garden) characteristics.79
Table H.13 – Zone Z (archive) characteristics .79
Table H.14 – Zone Z (offices) characteristics .80
Table H.15 – Zone Z (computer centre) characteristics.80
Table H.16 – Collection areas of structure and lines .80
Table H.17 – Expected annual number of dangerous events .81
–5
Table H.18 – Risk R - Values of risk components according to zones (values × 10 ).81
–5
Table H.19 –Composition of risk R components according to zones (values × 10 ) .81
–5
Table H.20 – Values of risk R according to solution chosen (values × 10 ) .82
Table H.21 – Structure characteristics .83
Table H.22 – Internal power system and relevant incoming power line characteristics .84
Table H.23 – Internal telecom system and relevant incoming line characteristics .84
Table H.24 – Zone Z (outside building) characteristics .85
Table H.25 – Zone Z (rooms block) characteristics .86
Table H.26 – Zone Z (operating block) characteristics .86
Table H.27 – Zone Z ( intensive care unity) characteristics.87
Table H.28 – Expected annual number of dangerous events .87
Table H.29 – Risk R – Risk components to be considered according to zones.88
Table H.30 – Risk R – Values of probability P for unprotected structure .88
Table H.31 – Risk R – Values of risk components for unprotected structure according
–5
to zones (values × 10 ) .89
–5
Table H.32 – Composition of risk R components according to zones (values × 10 ) .89
Table H.33 – Risk R – Values of probability P for the protected structure  according to
solution a).91
Table H.34 – Risk R – Values of probability P for protected structure according to
solution b).91

Table H.35 – Risk R – Values of probability P for the protected structure according to
solution c).92
–5
Table H.36 – Risk R – Values of risk according to solution chosen (values × 10 ).92
Table H.37 – Values of costs of loss relevant to zones (values in $ × 10 ) .93
Table H.38 – Values relevant to rates .93
Table H.39 – Risk R – Values of risk components for unprotected structure
–5
according to zones (values × 10 ) .94

62305-2  IEC:2006 –– 6 – 11 – 62305-2 © IEC:2006

Table H.40 – Amount of losses C and C (values in $) .94
L RL
Table H.41 – Costs C and C of protection measures (values in $) .95

P PM
Table H.42 – Annual saving of money (values in $).95

Table H.43 – Structure characteristics .96

Table H.44 – Zone Z parameters .96

Table H.45 – Internal power system and relevant incoming line parameters.97

Table H.46 – Internal telecom system and relevant incoming line parameters .97

Table H.47 – Protection measures to be adopted according to the height of the building

and its risk of fire .98

Table I.1 – Section S of line characteristics .100
Table I.2 – Section S of line characteristics .100
Table I.3 – End of line structure characteristics.101
Table I.4 – Expected annual number of dangerous events .101
Table I.5 – Risk R′ - Risk components relevant to sections S of the line .101
Table I.6 – Risk R′ - Values of failure currents and probabilities P′ for unprotected line.102
Table I.7 – Risk R′ - Values of risk components for unprotected line according to
–3
sections S of the line (values × 10 ) .103
Table I.8 – Risk R′ - Values of probabilities P′ for the protected line.104
Table I.9 – Risk R′ - Values of risk components for the line protected with SPDs
–3
installed in the transition point T and T with P = 0,03 (values × 10 ).104
1/2 a SPD
Table J.1 – Parameters for the user to change freely .105
Table J.2 – Limited subset of parameters to be changed by the user .105
Table J.3 – Fixed parameters (not to altered by the user) .107

62305-2 © IEC:200662305-2  IEC:2006 –– 7 – 13 –

INTERNATIONAL ELECTROTECHNICAL COMMISSION

___________
PROTECTION AGAINST LIGHTNING –

Part 2: Risk management
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62305-2 has been prepared by IEC technical committee 81:
Lightning protection.
The IEC 62305 series (Parts 1 to 5), is produced in accordance with the New Publications
Plan, approved by National Committees (81/171/RQ (2001-06-29)), which restructures and
updates, in a more simple and rational form, the publications of the IEC 61024 series, the
IEC 61312 series and the IEC 61663 series.
The text of this first edition of IEC 62305-2 is compiled from and replaces
– IEC 61662, first edition (1995) and its Amendment (1996).

62305-2  IEC:2006 –– 8 – 15 – 62305-2 © IEC:2006

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

FDIS Report on voting
81/263/FDIS 81/268/RVD
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 close as possible, in accordance with the ISO/IEC

Directives, Part 2.
IEC 62305 consists of the following parts, under the general title Protection against lightning:
Part 1: General principles
Part 2: Risk management
Part 3: Physical damage to structures and life hazard
Part 4: Electrical and electronic systems within structures
Part 5: Services
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
___________
To be published
62305-2 © IEC:200662305-2  IEC:2006 –– 9 – 17 –

INTRODUCTION
Lightning flashes to earth may be hazardous to structures and to services.

The hazard to a structure can result in

– damage to the structure and to its contents,

– failure of associated electrical and electronic systems,

– injury to living beings in or close to the structure.

Consequential effects of the damage and failures may be extended to the surroundings of the
structure or may involve its environment.
The hazard to services can result in
– damage to the service itself,
– failure of associated electrical and electronic equipment.
To reduce the loss due to lightning, protection measures may be required. Whether they are
needed, and to what extent, should be determined by risk assessment.
The risk, defined in this standard as the probable average annual loss in a structure and in a
service due to lightning flashes, depends on:
– the annual number of lightning flashes influencing the structure and the service;
– the probability of damage by one of the influencing lightning flashes;
– the mean amount of consequential loss.
Lightning flashes influencing the structure may be divided into
– flashes terminating on the structure,
– flashes terminating near the structure, direct to connected services (power, telecom-
munication lines, other services) or near the services.
Lightning flashes influencing the service may be divided into
– flashes terminating on the service,
– flashes terminating near the service or direct to a structure connected to the service.
Flashes to the structure or a connected service may cause physical damage and life hazards.
Flashes near the structure or service as well as flashes to the structure or service may cause

failure of electrical and electronic systems due to overvoltages resulting from resistive and
inductive coupling of these systems with the lightning current.
Moreover, failures caused by lightning overvoltages in users′ installations and in power supply
lines may also generate switching type overvoltages in the installations.
NOTE 1 Malfunctioning of electrical and electronic systems is not covered by the IEC 62305 series. Reference
should be made to IEC 61000-4-5 [1] .
NOTE 2 Information on assessment of the risk due to switching overvoltages is given in Annex F.
___________
Figures in square brackets refer to the bibliography.

62305-2  IEC:2006 –– 10 – 19 – 62305-2 © IEC:2006

The number of lightning flashes influencing the structure and the services depends on the
dimensions and the characteristics of the structure and of the services, on the environment

characteristics of the structure and the services, as well as on lightning ground flash density

in the region where the structure and the services are located.

The probability of lightning damage depends on the structure, the services, and the lightning

current characteristics; as well as on the type and efficiency of applied protection measures.

The annual mean amount of the consequential loss depends on the extent of damage and the

consequential effects which may occur as result of a lightning flash.

The effect of protection measures results from the features of each protection measure and
may reduce the damage probabilities or the amount of consequential loss.
The assessment of risk due to all possible effects of lightning flashes to structures and
services is given in this standard, which is a revised version of IEC 61662:1995 and its
Amendment 1:1996.
The decision to provide lightning protection may be taken regardless of the outcome of any
risk assessment where there is a desire that there be no avoidable risk.

62305-2 © IEC:200662305-2  IEC:2006 –– 11 – 21 –

PROTECTION AGAINST LIGHTNING –

Part 2: Risk management
1 Scope
This part of IEC 62305 is applicable to risk assessment for a structure or for a service due to
lightning flashes to earth.
Its purpose is to provide a procedure for the evaluation of such a risk. Once an upper
tolerable limit for the risk has been selected, this procedure allows the selection of
appropriate protection measures to be adopted to reduce the risk to or below the tolerable
limit.
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 60079-10:2002, Electrical apparatus for explosive gas atmosphere – Part 10:
Classification of hazardous areas
IEC 61241-10:2004, Electrical apparatus for use in the presence of combustible dust – Part
10: Classification of areas where combustible dusts are or may be present
IEC 62305-1, Protection against lightning – Part 1: General principles
IEC 62305-3, Protection against lightning – Part 3: Physical damage to structures and life
hazard
IEC 62305-4, Protection against lightning – Part 4: Electrical and electronic systems within
structures
IEC 62305-5, Protection against lightning – Part 5: Services
ITU-T Recommendation K.46:2000, Protection of telecommunication lines using metallic

symmetric conductors against lightning induced surges
ITU-T Recommendation K.47:2000, Protection of telecommunication lines using metallic
conductors against direct lightning discharges
3 Terms, definitions, symbols and abbreviations
For the purposes of this document, the following terms, definitions, symbols and
abbreviations, some of which have already been cited in Part 1 but are repeated here for ease
of reading, as well as those given in other parts of IEC 62305, apply.
___________
To be published
62305-2  IEC:2006 –– 12 – 23 – 62305-2 © IEC:2006

3.1 Terms and definitions
3.1.1
object to be protected
structure or service to be protected against the effects of lightning

3.1.2
structure to be protected
structure for which protection is required against the effects of lightning in accordance with

this standard
NOTE A structure to be protected may be a part of a larger structure.

3.1.3
structures with risk of explosion
structures containing solid explosives materials or hazardous zones as determined in
accordance with IEC 60079-10 and IEC 61241-10
NOTE For the purposes of this standard, only structures with hazardous zones type 0 or containing solid
explosive materials are considered.
3.1.4
structures dangerous to the environment
structures which may cause biological, chemical and radioactive emission as a consequence
of lightning (such as chemical, petrochemical, nuclear plants, etc).
3.1.5
urban environment
area with a high density of buildings or densely populated communities with tall buildings
NOTE ’Town centre’ is an example of an urban environment.
3.1.6
suburban environment
area with a medium density of buildings
NOTE ’Town outskirts’ is an example of a suburban environment.
3.1.7
rural environment
area with a low density of buildings.
NOTE ’Countryside’ is an example of a rural environment.
3.1.8
rated impulse withstand voltage level

U
w
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 standard, only withstand voltage between live conductors and earth is considered.
3.1.9
electrical system
system incorporating low voltage power supply components

62305-2 © IEC:200662305-2  IEC:2006 –– 13 – 25 –

3.1.10
electronic system
system incorporating sensitive electronic components such as communication equipment,

computer, control and instrumentation systems, radio systems, power electronic installations

3.1.11
internal systems
electrical and electronic systems within a structure

3.1.12
service to be protected
service connected to a structure for which protection is required against the effects of
lightning in accordance with this standard
3.1.13
telecommunication lines
transmission medium intended for communication between equipment that may be located in
separate structures, such as phone line and data line
3.1.14
power lines
transmission lines feeding electrical energy into a structure to power electrical and electronic
equipment located there, such as low voltage (LV) or high voltage (HV) electric mains
3.1.15
pipes
piping intended to convey a fluid into or out of a structure, such as gas pipe, water pipe, oil
pipe
3.1.16
dangerous event
lightning flash to the object to be protected or near the object to be protected
3.1.17
lightning flash to an object
lightning flash striking an object to be protected
3.1.18
lightning flash near an object
lightning flash striking close enough to an object to be protected that it may cause dangerous
overvoltages
3.1.19
number of dangerous events due to flashes to a structure
N
D
expected average annual number of dangerous events due to lightning flashes to a structure
3.1.20
number of dangerous events due to flashes to a service
N
L
expected average annual number of dangerous events due to lightning flashes to a service

62305-2  IEC:2006 –– 14 – 27 – 62305-2 © IEC:2006

3.1.21
number of dangerous events due to flashes near a structure

N
M
expected average annual number of dangerous events due to lightning flashes near a

structure
3.1.22
number of dangerous events due to flashes near a service

N
I
expected average annual number of dangerous events due to lightning flashes near a service

3.1.23
lightning electromagnetic impulse
LEMP
electromagnetic effects of lightning current
NOTE It includes conducted surges as well as radiated impulse electromagnetic field effects.
3.1.24
surge
transient wave appearing as overvoltage and/or overcurrents caused by LEMP
NOTE Surges caused by LEMP can arise from (partial) lightning currents, from induction effects into installation
loops and as remaining threats downstream of SPD.
3.1.25
node
point on a service line at a which surge propagation can be assumed to be neglected
NOTE Examples of nodes are a point on a power line branch distribution at a HV/LV transformer, a multiplexer on
a telecommunication line or SPD installed along the line conforming to IEC 62305-5.

3.1.26
physical damage
damage to a structure (or to its contents) or to a service due to mechanical, thermal, chemical
or explosive effects of lightning.
3.1.27
injury to living beings
injuries, including loss of life, to people or to animals due to touch and step voltages caused
by lightning
3.1.28
failure of electrical and electronic systems
permanent damage of electrical and electronic systems due to LEMP
3.1.29
failure current
I
a
minimum peak value of lightning current that will cause damage in a line
3.1.30
probability of damage
P
X
probability that a dangerous event will cause damage to or in the object to be protected

62305-2 © IEC:200662305-2  IEC:2006 –– 15 – 29 –

3.1.31
loss
L
X
mean amount of loss (humans and goods) consequent to a specified type of damage due to a

dangerous event, relative to the value (humans and goods) of the object to be protected

3.1.32
risk
R
value of probable average annual loss (humans and goods) due to lightning, relative to the

total value (humans and goods) of the object to be protected

3.1.33
risk component
R
X
partial risk depending on the source and the type of damage
3.1.34
tolerable risk
R
T
maximum value of the risk which can be tolerated for the object to be protected
3.1.35
zone of a structure
Z
S
part of a structure with homogeneous characteristics where only one set of parameters is
involved in assessment of a risk component
3.1.36
section of a service
S
S
part of a service with homogeneous characteristics where only one set of parameters is
involved in the assessment of a risk component
3.1.37
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).
3.1.38
lightning protection level
LPL
number related to a set of lightning current parameter values 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.
3.1.39
protection measures
measures to be adopted in the object to be protected, in order to reduce the risk

62305-2  IEC:2006 –– 16 – 31 – 62305-2 © IEC:2006

3.1.40
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.

3.1.41
LEMP protection measures system

LPMS
complete system of protection measures for internal sy
...