IEC 62305-1:2024

Protection against lightning - Part 1: General principles

IEC 62305-1:2024 provides general principles for the protection of structures against lightning, including their installations and contents, as well as persons.
The following cases are outside the scope of this document:
- railway systems;
- vehicles, ships, aircraft, offshore installations;
- underground high-pressure pipelines;
- pipe, power and telecommunication lines separated from the structure;
- nuclear power plants.
This third edition cancels and replaces the second edition published in 2010. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) reference to the IEC 62561 series is made in Annex D to provide a link to relevant lightning protection system components according to the IEC 62561 series;
b) risk management introduces the concept of types of loss with public relevance;
c) the concept of frequency of damage that can impair the availability of the internal systems within the structure has been introduced;
d) surge currents due to lightning flashes have been more accurately specified for SPD dimensioning in low-voltage power systems and in telecommunication systems.

Protection contre la foudre - Partie 1: Principes généraux

L'IEC 62305-1:2024 fournit des principes généraux de protection des structures contre la foudre, y compris leurs installations, leur contenu et les personnes qui s'y trouvent.
Les cas suivants ne relèvent pas du domaine d'application du présent document:
- chemins de fer;
- véhicules, navires, avions, installations en mer;
- canalisations enterrées à haute pression;
- canalisations, lignes de puissance et de communication séparées de la structure;
- centrales nucléaires de puissance.
Cette troisième édition annule et remplace la deuxième édition parue en 2010. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) à l'Annexe D, il est fait référence à la série IEC 62561 pour faire le lien avec les composants des systèmes de protection contre la foudre correspondants selon la série IEC 62561;
b) la gestion des risques introduit le concept des types de pertes qui revêtent une importance publique;
c) introduction du concept de fréquence des dommages qui peuvent influencer la disponibilité des réseaux internes à la structure;
d) les courants de surcharge dus aux coups de foudre ont été spécifiés avec davantage de précision pour le dimensionnement des SPD dans des systèmes d'alimentation basse tension et dans les réseaux de communication.

General Information

• Status: Published
• Publication Date: 11-Sep-2024
• ICS: 29.020 - Electrical engineering in general
• ICS: 33.160.40 - Video systems
• ICS: 91.120.40 - Lightning protection
• Technical Committee: TC 81 - Lightning protection
• Drafting Committee: MT 8 - TC 81/MT 8
• Current Stage: PPUB - Publication issued
• Start Date: 12-Sep-2024
• Completion Date: 05-Jan-2024

Relations

• Revises: IEC 62305-1:2010 - Protection against lightning - Part 1: General principles
• Effective Date: 05-Sep-2023

IEC 62305-1:2024 Overview

IEC 62305-1:2024 is the third edition of the international standard titled Protection against lightning – Part 1: General principles, published by the International Electrotechnical Commission (IEC). This standard establishes the fundamental principles for protecting structures, their internal installations, contents, and people from the risks posed by lightning strikes. It serves as a technical revision of the 2010 second edition, incorporating key updates based on current technology and risk management practices.

The scope of IEC 62305-1:2024 specifically targets structures on land and excludes railway systems, vehicles, ships, aircraft, offshore platforms, underground high-pressure pipelines, separated pipe and telecommunication lines, and nuclear power plants. The standard emphasizes the assessment and mitigation of lightning hazards by defining risks, types of losses, protection methods, and electrical parameters necessary for effective lightning protection systems.

Key Topics in IEC 62305-1:2024

• Lightning Current Parameters: Defines characteristics of lightning currents including amplitude, duration, and frequency, crucial for designing protective measures.

• Damage Analysis: Differentiates damage to physical structures from damage to internal systems and persons, outlining sources and causes of lightning-related harm.

• Risk and Frequency Assessment: Introduces the concept of loss types with public relevance and considers the frequency of damage affecting internal system availability.

• Protection Measures: Covers strategies to reduce injuries, physical damage, and failures of internal electrical and electronic systems within structures.

• Lightning Protection Levels (LPLs): Classifies protective measures from lower to higher robustness, matched to risk severity and expected lightning parameters.

• Lightning Protection Zones (LPZs): Details zoning inside and outside protected structures to enhance tailored protection based on exposure.

• Surge Protective Devices (SPDs): Addresses the proper dimensioning of SPDs for low-voltage power and telecommunication systems using updated surge current specifications.

• Test Parameters: References the IEC 62561 series and defines test parameters for lightning protection components such as air termination systems, down conductors, and earth terminations.

Practical Applications

IEC 62305-1:2024 provides organizations and engineers with a comprehensive framework to design and implement effective lightning protection systems (LPS). Applications include:

• Structural Lightning Protection: Ensures buildings and infrastructure are safeguarded against strikes via air terminals, down conductors, and earthing systems.

• Internal Systems Protection: Minimizes failure risk of sensitive electrical and telecommunication installations due to surge currents caused by lightning.

• Risk Management: Helps facility managers evaluate the need for protection based on risk assessments, loss types, and frequency of lightning events.

• Surge Protection Planning: Guides the installation of surge protective devices consistent with realistic lightning current parameters for enhanced system resiliency.

• Safety for Occupants: Defines methods to reduce injury risks to human beings within protected structures from direct or indirect lightning effects.

Related Standards

IEC 62305-1:2024 is part of the IEC 62305 series on lightning protection, which also includes:

• IEC 62305-2: Risk Management – Provides detailed assessment methodologies to quantify lightning risk to structures and people.

• IEC 62305-3: Physical Damage to Structures and Life Hazard – Focuses on detailed protection against physical destruction and related safety hazards.

• IEC 62305-4: Electrical and Electronic Systems within Structures – Addresses protection of internal systems from transient overvoltages caused by lightning.

Additionally, IEC 62305-1 references the IEC 62561 series for lightning protection system components, detailing test and performance standards for air-termination, down conductors, earth termination, and connecting components.

---

Keywords: lightning protection standard, IEC 62305-1, lightning risk assessment, lightning protection levels, surge protective devices, lightning current parameters, lightning protection zones, IEC lightning standards, electrical surge protection, lightning damage prevention, structure safety, internal system protection.

Standards Content (Sample)

IEC 62305-1 ®
Edition 3.0 2024-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Protection against lightning –
Part 1: General principles
Protection contre la foudre –
Partie 1: Principes généraux
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IEC 62305-1 ®
Edition 3.0 2024-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Protection against lightning –

Part 1: General principles
Protection contre la foudre –
Partie 1: Principes généraux
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.020, 91.120.40 ISBN 978-2-8322-8002-7

– 2 – IEC 62305-1:2024 © IEC 2024
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 10
4 Lightning current parameters . 17
5 Damage due to lightning . 18
5.1 Damage to a structure . 18
5.1.1 General . 18
5.1.2 Effects of lightning on a structure . 18
5.1.3 Sources and causes of damage to a structure . 19
5.2 Types of loss . 20
6 Need for lightning protection . 21
6.1 Risk and frequency . 21
6.2 Need for lightning protection for reduction of risk R . 22
6.3 Need for lightning protection for reduction of frequency of damage F . 22
7 Protection measures . 23
7.1 General . 23
7.2 Protection measures to reduce injury to human beings by electric shock . 23
7.3 Protection measures to reduce physical damage. 24
7.4 Protection measures to reduce failure of internal systems . 24
7.5 Protection measures selection . 24
8 Basic criteria for protection of structures . 24
8.1 General . 24
8.2 Lightning protection levels (LPLs) . 25
8.3 Lightning protection zones (LPZs) . 27
8.4 Protection of structures . 29
8.4.1 Protection to reduce physical damage and life hazard . 29
8.4.2 Protection to reduce the failure of internal systems . 30
Annex A (informative) Parameters of lightning current . 31
A.1 Lightning flashes to earth . 31
A.2 Lightning current parameters . 34
A.3 Fixing the maximum lightning current parameters for LPL I . 39
A.3.1 General . 39
A.3.2 First positive stroke and long stroke . 39
A.3.3 First negative stroke . 40
A.3.4 Subsequent stroke . 40
A.4 Fixing the minimum lightning current parameters . 40
Annex B (informative) Time functions of the lightning current for analysis purposes . 42
Annex C (informative) Simulation of the lightning current for test purposes . 47
C.1 General . 47
C.2 Simulation of the specific energy of the first positive stroke and the charge of
the long stroke . 47
C.3 Simulation of the front current steepness of the impulses . 48

Annex D (informative) Test parameters simulating the effects of lightning current on
LPS components . 51
D.1 General . 51
D.2 Current parameters relevant to the point of strike . 51
D.3 Current sharing . 52
D.4 Effects of lightning current causing possible damage . 53
D.4.1 Thermal effects . 53
D.4.2 Mechanical effects . 57
D.4.3 Combined effects . 61
D.4.4 Sparking . 61
D.4.5 Soil ionization . 61
D.5 LPS components, relevant problems and test parameters . 61
D.5.1 General . 61
D.5.2 Air terminations . 61
D.5.3 Down conductors . 62
D.5.4 Connecting components . 63
D.5.5 Earth terminations . 64
D.6 Surge protective devices (SPDs) . 64
D.6.1 General . 64
D.6.2 SPD containing spark gaps . 64
D.6.3 SPD containing metal-oxide varistors . 65
D.7 Summary of the test parameters to be adopted in testing LPS components . 66
Annex E (informative) Surge currents due to lightning at different installation points . 67
E.1 General . 67
E.2 Surge currents due to flashes to the structure (source of damage S1) . 67
E.2.1 Surge currents flowing through external conductive parts and lines
connected to the structure . 67
E.2.2 Factors influencing the sharing of the lightning current and related
charge in power lines . 67
E.2.3 Surge currents flowing through line conductors connected to the
structure . 68
E.2.4 Surge currents flowing through conductive parts and cables internal to
the structure connected to LPS . 69
E.2.5 Surge currents flowing through cables connected to different points of
the earth-termination system within the same earth-termination system . 70
E.3 Surge currents due to flashes to lines (source of damage S3) . 70
E.4 Surges due to flashes near the lines (source of damage S4) . 71
E.5 Surge currents due to induction effects (sources of damage S1 or S2) . 71
E.5.1 General . 71
E.5.2 Surges inside an unshielded LPZ 1 . 72
E.5.3 Surges inside shielded LPZs . 72
E.6 Conventional surge currents . 72
Bibliography . 75

Figure 1 – Connection between the various parts of the IEC 62305 series . 9
Figure 2 – LPZ defined by an LPS (IEC 62305-3) . 28
Figure 3 – LPZ defined by LPS and SPM (IEC 62305-4) . 29
Figure A.1 – Definitions of impulse current parameters according to IEC 62475 [7] . 31
Figure A.2 – Definitions of long duration stroke parameters . 32

– 4 – IEC 62305-1:2024 © IEC 2024
Figure A.3 – Schematic representation (not to scale) of possible components of
downward flashes (typical in flat territory and to lower structures) and multiple strokes
downward flashes . 32
Figure A.4 – Schematic representation (not to scale) of possible components of
upward flashes (typical of exposed or higher structures or both) . 33
Figure A.5 – Cumulative frequency distribution of lightning current parameters (dotted
line through 50 % value) . 38
Figure B.1 – Shape of the current rise of the first positive stroke . 43
Figure B.2 – Shape of the current tail of the first positive stroke. 43
Figure B.3 – Shape of the current rise of the first negative stroke . 44
Figure B.4 – Shape of the current tail of the first negative stroke . 44
Figure B.5 – Shape of the current rise of the subsequent negative strokes . 45
Figure B.6 – Shape of the current tail of the subsequent negative strokes . 45
Figure B.7 – Amplitude density of the lightning current according to LPL I . 46
Figure C.1 – Example test generator for the simulation of the specific energy of the
first positive stroke and the charge of the long stroke . 48
Figure C.2 – Definition of the current steepness in accordance with Table C.3 . 49
Figure C.3 – Example test generator for the simulation of the front steepness of the
first positive stroke for large test items . 49
Figure C.4 – Example test generator for the simulation of the front steepness of the
subsequent negative strokes for large test items . 50
Figure D.1 – General arrangement of two conductors for the calculation of
electrodynamic force . 58
Figure D.2 – Typical conductor arrangement in an LPS . 59
Figure D.3 – Diagram of the stresses F for the configuration of Figure D.2 . 59
Figure D.4 – Force per unit length F’ along the horizontal conductor of Figure D.2 . 60

Table 1 – Effects of lightning on typical structures . 19
Table 2 – Sources of damage, causes of damage, types of loss according to the point
of strike . 21
Table 3 – Maximum values of lightning parameters according to LPLs . 26
Table 4 – Minimum values of lightning parameters and related rolling sphere radius
corresponding to LPLs . 26
Table 5 – Probabilities for the limits of the lightning current parameters . 26
Table A.1 – Tabulated values of lightning current parameters (CIGRE [9], [10], [11]) . 35
Table A.2 – Logarithmic normal distribution of lightning current parameters –
Mean µ and dispersion σ calculated from 5 % and 95 % values
log
(CIGRE [9], [10], [11]) . 36
Table A.3 – Values of probability P as function of the lightning current I peak value . 37
Table B.1 – Parameters for Equation (B.1) . 42
Table C.1 – Test parameters of the first positive stroke . 48
Table C.2 – Test parameters of the long stroke . 48
Table C.3 – Test parameters of the strokes. 49
Table D.1 – Summary of the lightning threat parameters to be considered in the
calculation of the test values for the different LPS components and for the

different LPLs . 52
Table D.2 – Physical characteristics of typical materials used in LPS components . 55

Table D.3 – Temperature rise for conductors of different sections as a function of W/R . 55
Table E.1 – Conventional surge currents due to lightning flashes on low-voltage
systems . 73
Table E.2 – Conventional surge currents due to lightning flashes on telecommunication
systems . 74

– 6 – IEC 62305-1:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PROTECTION AGAINST LIGHTNING –

Part 1: General principles
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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IEC 62305-1 has been prepared by IEC technical committee 81: Lightning protection. It is an
International Standard.
This third edition cancels and replaces the second edition published in 2010. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) reference to the IEC 62561 series [1] is made in Annex D to provide a link to relevant
lightning protection system components according to the IEC 62561 series;
___________
Numbers in square brackets refer to the Bibliography.

b) risk management introduces the concept of types of loss with public relevance;
c) the concept of frequency of damage that can impair the availability of the internal systems
within the structure has been introduced;
d) surge currents due to lightning flashes have been more accurately specified for SPD
dimensioning in low-voltage power systems and in telecommunication systems.
The text of this International Standard is based on the following documents:
Draft Report on voting
81/737/FDIS 81/756/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 62305 series, published under the general title Protection against
lightning, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
– 8 – IEC 62305-1:2024 © IEC 2024
INTRODUCTION
There are no devices or methods capable of modifying the natural weather phenomena to the
extent that they can prevent lightning discharges. Lightning flashes to, or nearby, structures (or
lines connected to the structures) are hazardous to people, to the structures themselves, their
contents and installations as well as to lines. This is why the application of lightning protection
measures is essential.
The need for protection, the economic benefits of installing protection measures, and the
selection of adequate protection measures should be determined in terms of risk management.
Risk management is the subject of IEC 62305-2 [2].
NOTE In Germany, the need for lightning protection is determined by, and the class of required LPS shall be
selected according to, a national annex to the third edition of IEC 62305-1 (including an option for a risk assessment
following the third edition of IEC 62305-2).
Protection measures considered in the IEC 62305 series have been proven to be effective in
risk reduction.
All measures for protection against lightning form the overall lightning protection. For practical
reasons the criteria for design, installation and maintenance of lightning protection measures
are considered in two separate groups:
– the first group concerning protection measures to reduce physical damage and life hazard
in a structure is given in IEC 62305-3;
– the second group concerning protection measures to reduce failures of electrical and
electronic systems in a structure is given in IEC 62305-4.
The connection between the parts of the IEC 62305 series is illustrated in Figure 1.
NOTE The implementation of an IEC 62793 [3] compliant TWS in the protection measures for a structure can assist
in reducing physical damage, life hazard, and failure of electrical and electronic systems.

Figure 1 – Connection between the various parts of the IEC 62305 series

– 10 – IEC 62305-1:2024 © IEC 2024
PROTECTION AGAINST LIGHTNING –

Part 1: General principles
1 Scope
This part of IEC 62305 provides general principles for the protection of structures against
lightning, including their installations and contents, as well as persons.
The following cases are outside the scope of this document:
– railway systems;
– vehicles, ships, aircraft, offshore installations;
– underground high-pressure pipelines;
– pipe, power and telecommunication lines separated from the structure;
– nuclear power plants.
The IEC 62305 series should be considered as a minimum requirement for these structures.
Until any further information by CIGRE is available the lightning current parameters described
in this document can be applied also for offshore installations.
NOTE 1 In these cases, structures usually fall under special regulations produced by various specialized
authorities. For structures (subsidiary or others) not falling under such special regulations, the IEC 62305 series still
applies.
NOTE 2 Lightning protection of wind turbines is also covered by IEC 61400-24 [4].
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 62305-3:2024, Protection against lightning – Part 3: Physical damage to structures and life
hazard
IEC 62305-4:2024, Protection against lightning – Part 4: Electrical and electronic systems within
structures
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp

3.1
lightning flash to earth
electrical discharge of atmospheric origin between cloud and earth consisting of one or more
strokes
3.2
downward flash
lightning flash initiated by a downward leader from cloud to earth
Note 1 to entry: A downward flash consists of a first current short stroke, which can be followed by other subsequent
short strokes. One or more short strokes can be also followed by a long stroke.
3.3
upward flash
lightning flash initiated by an upward leader from an earthed structure to cloud
Note 1 to entry: An upward flash consists of a first long stroke with or without multiple superimposed impulses. One
or more impulses can be followed by a long stroke.
3.4
lightning stroke
single electrical discharge in a lightning flash to earth
3.5
short stroke
part of the lightning flash which corresponds to an impulse current
Note 1 to entry: The impulse current has a time T to the half peak value on the tail typically less than 2 ms (see
Figure A.1).
3.6
long stroke
part of the lightning flash which corresponds to a continuing current
Note 1 to entry: The duration time T of this continuing current is typically more than 2 ms and less than 1 s
LONG
(see Figure A.2).
3.7
multiple strokes lightning flash
lightning flash consisting on average of three to four strokes, with a typical time interval between
them of about 50 ms
Note 1 to entry: Events having up to a few dozen strokes with intervals between them ranging from 10 ms to 250 ms
have been reported.
3.8
point of strike
point where a lightning flash strikes the earth or a structure (e.g. building, LPS, line, tree)
Note 1 to entry: A lightning flash can have more than one point of strike.
3.9
lightning current
i
current flowing at the point of strike
3.10
current peak value
I
maximum value of the lightning current

– 12 – IEC 62305-1:2024 © IEC 2024
3.11
average steepness of the current front
di/dt
maximum current of the impulse I divided by the front time of the impulse T
Note 1 to entry: See 3.10 and 3.12 and Figure A.1.
3.12
front time of impulse current
T
virtual parameter defined as 1,25 times the time interval between the instants when the 10 %
and 90 % of the peak value are reached
SEE: Figure A.1.
3.13
virtual origin of impulse current
O
point of intersection with the time axis of a straight line drawn through the 10 % and the 90 %
reference points on the stroke current front preceding by 0,1 T that instant at which the current
attains 10 % of its peak value
SEE: Figure A.1.
3.14
time to half value on the tail of impulse current
T
virtual parameter defined as the time interval between the virtual origin O and the instant at
which the current has decreased to half the peak value on the tail
SEE: Figure A.1.
3.15
flash duration
T
time for which the lightning current flows at the point of strike
3.16
duration of long stroke current
T
LONG
time duration during which the current in a long stroke is between 10 % of the peak value during
the increase of the continuing current and 10 % of the peak value during the decrease of the
continuing current
SEE: Figure A.2.
3.17
flash charge
Q
FLASH
value resulting from the time integral of the lightning current for the entire lightning flash
duration
3.18
short stroke charge
Q
SHORT
value resulting from the time integral of the lightning current in an impulse

3.19
long stroke charge
Q
LONG
value resulting from the time integral of the lightning current in a long stroke
3.20
specific energy
W/R
value resulting from the time integral of the square of the lightning current for the entire flash
duration
Note 1 to entry: The specific energy represents the energy dissipated by the lightning current in a unit resistance.
3.21
specific energy of the impulse current
value resulting from the time integral of the square of the lightning current for the duration of
the impulse
Note 1 to entry: The specific energy in a long stroke current is negligible.
3.22
structure to be protected
any place, facility or building suitable to contain persons, animals, materials or systems
Note 1 to entry: A structure to be protected can be part of a larger structure.
3.23
line
external power line or telecommunication line connected to the structure to be protected
3.24
telecommunication line
line intended for communication between equipment that can be located in separate structures,
such as a phone line and a data line
3.25
power line
distribution line 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
3.26
lightning flash to a structure
lightning flash striking a structure
3.27
lightning flash near a structure
lightning flash striking close enough to a structure that it can cause dangerous overvoltages
3.28
lightning flash to a line
lightning flash striking a line connected to a structure
3.29
lightning flash near a line
lightning flash striking close enough to a line connected to a structure that it can cause
dangerous overvoltages within the structure

– 14 – IEC 62305-1:2024 © IEC 2024
3.30
dangerous event
lightning flash to or near a structure, or to or near a line connected to the structure that can
cause damage within the structure
3.31
dangerous sparking
spark inside the structure where lightning current flows triggering fire or explosion or leading to
mechanical and chemical effects which can also endanger the environment
3.32
electrical system
system incorporating low-voltage power supply components
3.33
electronic system
system incorporating sensitive electronic components such as telecommunication equipment,
computer, control and instrumentation systems, radio systems, power electronic installations
3.34
internal systems
electrical and electronic systems of a structure
Note 1 to entry: Internal systems may for example be located on the roof of the structure provided they are
connected internally to the structure.
3.35
physical damage
damage to a structure (or to its contents) due to mechanical, thermal, chemical and explosive
effects of lightning
3.36
injury to human beings
injuries to, including loss of life of, people, resulting from lightning
3.37
failure of internal systems
damage of internal systems due to LEMP
3.38
lightning electromagnetic impulse
LEMP
fast time-varying electromagnetic field emitted by lightning which can create surges via
resistive, inductive and capacitive coupling to circuits
3.39
surge
transient in lines and equipment created by LEMP that appears as overvoltage or overcurrent
or both
3.40
lightning protection zone
LPZ
zone where the lightning electromagnetic environment is defined
Note 1 to entry: The zone boundaries of an LPZ are not necessarily physical boundaries (e.g. walls, floor and
ceiling).
3.41
frequency of damage
F
value of the annual number of damaging events due to LEMP which can occur to the internal
systems of a structure
3.42
tolerable frequency of damage
F
T
maximum value of the frequency of damage which can be tolerated for the internal systems of
the structure or a zone to be protected
3.43
loss
L
mean amount of a specified type of loss consequent to a dangerous event in the considered
zone of a structure
3.44
loss of public relevance
loss which will result in consequences that will affect more than those involved in the decision-
making process such as external consequences, injury to human beings, unavailability of
services provided to the public, including physical damage, damage to the environment, and
costs required to be paid by the public
EXAMPLE The costs of emergency measures to limit the damage, the costs resulting from loss of the structure and
production, the costs of reconstruction.
3.45
service
function performed by the internal systems of the structure to supply a specific need
3.46
service of public relevance
service provided to the public as well as service where the heritage of cultural interest is
involved
3.47
risk
R
probable average annual loss due to lightning, in a structure or in a considered zone of the
structure
3.48
tolerable risk
R
T
maximum value of the risk which can be tolerated for the structure to be protected
3.49
lightning protection level
LPL
number related to a set of lightning current parameters values relevant to the probability that
the associated maximum and minimum design values will not be exceeded in naturally occurring
lightning
Note 1 to entry: The lightning protection level is used to design protection measures according to the relevant set
of lightning current parameters.

– 16 – IEC 62305-1:2024 © IEC 2024
3.50
protection measures
measures adopted for the structure to be protected in order to reduce the risk
3.51
lightning protection
LP
measures taken for the protection of structures against lightning, including their internal
systems and contents, as well as persons, in general consisting of an LPS and SPM
3.52
lightning protection system
LPS
complete system used to reduce injury to human beings and physical damage due to lightning
flashes to a structure
Note 1 to entry: A lightning protection system consists of both external and internal lightning protection systems.
To protect internal systems against the effects of LEMP, measures according to IEC 62305-4 are necessary.
3.53
external lightning protection system
part of the LPS consisting of an air-termination system, a down-conductor system and an earth-
termination system
3.54
internal lightning protection system
part of the LPS consisting of lightning equipotential bonding or electrical separation of an
external LPS or both
3.55
air-termination system
part of an external LPS using metallic elements such as rods, masts, mesh conductors or
catenary wires intended to intercept lightning flashes
3.56
down-conductor system
part of an external LPS intended to conduct lightning current from the air-termination system to
the earth-termination system
3.57
earth-termination system
part of an external LPS which is intended to conduct and disperse lightning current into the
earth
3.58
external conductive parts
extended metal items entering or leaving the structure to be protected such as pipe works, cable
metallic elements, metal ducts which can carry a part of the lightning current
3.59
lightning equipotential bonding
EB
bonding to the LPS of separated metallic parts, by direct conductive connections or via surge
protective devices, to reduce potential differences caused by lightning current
3.60
conventional earthing impedance
ratio of the peak values of the earth-termination voltage and the earth-termination current which,
in general, do not occur simultaneously

3.61
surge protection measures
SPM
measures taken to protect internal systems against the effects of LEMP
Note 1 to entry: Surge protection measures are part of the overall lightning protection.
3.62
electromagnetic shield
screen of conductive material intended to reduce the penetration of a time-varying
electromagnetic field into the structure or part of the structure to be protected, used to reduce
failures of internal systems
3.63
surge protective device
SPD
device that contains at least one non-linear component and that is intended to limit transient
overvoltages and divert surge currents
3.64
coordinated SPD system
set of SPDs properly selected, coordinated and installed to form a system intended to reduce
failures of internal systems
3.65
isolating interfaces
devices which are capable of reducing conducted surges on lines entering the LPZ
Note 1 to entry: Isolating interfaces include isolation transformers with an earthed screen between windings, metal
free fibre optic cables and opto-isolators.
Note 2 to entry: The insul
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