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For the collection area for lightning strikes near a line we have In case of a direct lightning strike to the ground near an incom-
(Figure 3.2.3.3): ing line (S4):
P Z Failure of electrical / electronic systems
A = 4000 L
I L A detailed description of these probabilities of damage can
be found in Annex B of IEC 62305-2 (EN 62305-2). The prob-
where L L is the length of the line section. If the length of the abilities of damage can be either selected from tables or they
line section is unknown, a worst case value of L L = 1000 m result from a combination of different influencing factors.
should be assumed.
In this context, it must be observed that, as a general rule,
other deviating values are possible if they are based on de-
If the line has more than one section, the values of N L and tailed examinations or assessments. In the following, a short
N I must be calculated for each relevant line section. The sec- overview of the individual probabilities of damage is given.
tions between the structure and the first node must be consi- More detailed information can be found in IEC 62305-2
dered (maximum distance from the structure must not exceed (EN 62305-2).
1000 m).
If more than one line enters the structure on different paths, Probabilities of damage in case of direct lightning
each line must be calculated individually. However, if more than strikes
one line enters the structure on the same path, only the line with The values of the probability of damage P A that living beings
the most unfavourable properties must be calculated, in other are injured by electric shock due to touch and step voltage
words the line with the maximum N L and N I values connected caused by a direct lightning strike to the structure depend on
to the internal systems with the lowest insulation strength the type of lightning protection system and additional protec-
(tele communication line opposite to power line, unshielded tion measures:
line opposite to shielded line, low-voltage power line oppo-
site to high-voltage power line with high-voltage / low-voltage P = P TA P B
A
transformer, etc.). If the collection areas of lines overlap, the
overlapped areas should only be considered once. P TA describes the typical protection measures against touch
and step voltages (Table 3.2.4.1). P B depends on the class of
LPS as per IEC 62305-3 (EN 62305-3) (Table 3.2.4.2).
3.2.4 Probabilities of damage If more than one protection measure is taken, the value of P TA
The parameter “probability of damage” defines the probability is the product of the corresponding values. Moreover, it must
that a dangerous event causes certain damage. The probability be observed that the protection measures to reduce P A are only
of damage may have a maximum value of 1 (meaning that effective in structures which are protected by a lightning pro-
every dangerous event causes damage). There are the follow- tection system (LPS) or which consist of a continuous metal or
ing eight probabilities of damage: reinforced concrete framework acting as a natural LPS provided
that equipotential bonding and earthing requirements as per
In case of a direct lightning strike to a structure (S1): IEC 62305-3 (EN 62305-3) are fulfilled. Chapter 5 provides
P A Injury to living beings by electric shock more detailed information on protection measures.
The probability of physical damage P B (fire, explosion, me-
P B Physical damage (fire, explosion, mechanical and chanical or chemical reactions inside or outside a structure as
chemical reactions) a result of a direct lightning strike) can be selected from Table
P C Failure of electrical / electronic systems 3.2.4.2.
The probability P C that a direct lightning strike to a structure
In case of a lightning strike to the ground near a structure will cause failure of internal systems depends on the coordi-
(S2): nated SPDs installed:
P M Failure of electrical / electronic systems
P = P C
C SPD LD
In case of a direct lightning strike to an incoming line (S3):
P SPD depends on the coordinated SPD system according to
P U Injury to living beings by electric shock
IEC 62305-4 (EN 62305-4) and on the lightning protection
P V Physical damage (fire, explosion, mechanical and level (LPL) for which the SPDs are dimensioned. The values
chemical reactions) of P SPD are given in Table 3.2.4.3. A coordinated SPD sys-
P W Failure of electrical / electronic systems tem only reduces P C if the structure is protected by an LPS or

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