GB/T 21714.1-2026 Protection against lightning – Part 1: General principles
1 Scope
This part 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 GB/T 21714 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 GB/T 21714 series still applies.
Note 2: Lightning protection of wind turbines is also covered by IEC 61400-24.
Note 3: In this document, the term "structures" generally refers to structures.
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.
GB/T 21714.3-2026 Protection against lightning - Part 3: Physical damage to structures and life hazard
GB/T 21714.4-2026 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:
- ISO Online browsing platform: available at https://www.iso.org/obp;
- IEC Electropedia: available at https://www.electropedia.org/.
3.1
lightning flash to earth; cloud-to-ground lightning
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: 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: 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: The impulse current has a time T2 to the half peak value on the tail typically less than 2 ms (see Figure A.1 in Annex A).
3.6
long stroke
part of the lightning flash which corresponds to a continuing current
Note: The duration time TLONG of this continuing current (the time interval from the 10 % current peak point on the wavefront to the 10 % current peak point on the wavetail) is typically more than 2 ms and less than 1 s (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: 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: 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
3.11
average steepness of the current front
di/dt
maximum current of the impulse I divided by the front time of the impulse T1
Note 1: See 3.10 and 3.12 and Figure A.1.
Note 2: The wavefront is also referred to as the front of the wave.
3.12
front time of impulse current
T1
virtual parameter defined as 1.25 times the time interval between the instants when the 10 % and 90 % of the peak value are reached
Note 1: See Figure A.1.
Note 2: The wavefront is also referred to as the front of the wave.
3.13
virtual origin of impulse current
O1
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 T1 that instant at which the current attains 10 % of its peak value
Note: See Figure A.1.
3.14
time to half value on the tail of impulse current
T2
virtual parameter defined as the time interval between the virtual origin O1 and the instant at which the current has decreased to half the peak value on the tail
Note: 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
TLONG
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
Note: See Figure A.2.
3.17
flash charge
QFLASH
value resulting from the time integral of the lightning current for the entire lightning flash duration
3.18
short stroke charge
QSHORT
value resulting from the time integral of the lightning current in an impulse
3.19
long stroke charge
QLONG
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: 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: 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: 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
Example: 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
Example: The 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
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
GB/T 21714.1-2026 Protection against lightning – Part 1: General principles
1 Scope
This part 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 GB/T 21714 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 GB/T 21714 series still applies.
Note 2: Lightning protection of wind turbines is also covered by IEC 61400-24.
Note 3: In this document, the term "structures" generally refers to structures.
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.
GB/T 21714.3-2026 Protection against lightning - Part 3: Physical damage to structures and life hazard
GB/T 21714.4-2026 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:
- ISO Online browsing platform: available at https://www.iso.org/obp;
- IEC Electropedia: available at https://www.electropedia.org/.
3.1
lightning flash to earth; cloud-to-ground lightning
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: 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: 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: The impulse current has a time T2 to the half peak value on the tail typically less than 2 ms (see Figure A.1 in Annex A).
3.6
long stroke
part of the lightning flash which corresponds to a continuing current
Note: The duration time TLONG of this continuing current (the time interval from the 10 % current peak point on the wavefront to the 10 % current peak point on the wavetail) is typically more than 2 ms and less than 1 s (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: 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: 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
3.11
average steepness of the current front
di/dt
maximum current of the impulse I divided by the front time of the impulse T1
Note 1: See 3.10 and 3.12 and Figure A.1.
Note 2: The wavefront is also referred to as the front of the wave.
3.12
front time of impulse current
T1
virtual parameter defined as 1.25 times the time interval between the instants when the 10 % and 90 % of the peak value are reached
Note 1: See Figure A.1.
Note 2: The wavefront is also referred to as the front of the wave.
3.13
virtual origin of impulse current
O1
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 T1 that instant at which the current attains 10 % of its peak value
Note: See Figure A.1.
3.14
time to half value on the tail of impulse current
T2
virtual parameter defined as the time interval between the virtual origin O1 and the instant at which the current has decreased to half the peak value on the tail
Note: 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
TLONG
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
Note: See Figure A.2.
3.17
flash charge
QFLASH
value resulting from the time integral of the lightning current for the entire lightning flash duration
3.18
short stroke charge
QSHORT
value resulting from the time integral of the lightning current in an impulse
3.19
long stroke charge
QLONG
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: 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: 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: 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
Example: 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
Example: The 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
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
