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if the structure consists of a continuous metal or reinforced distribution). The same annexes can also be used for SPDs with
concrete framework acting as a natural LPS provided that higher probabilities of P SPD .
the equipotential bonding and earthing requirements as per The factor C LD considers the shielding, earthing and insulation
IEC 62305-3 (EN 62305-3) are observed. The values of P SPD may conditions of the line connected to the internal system. The
be reduced if the selected SPDs have better protection charac- values of C LD are given in Table 3.2.4.4.
teristics (higher current carrying capability I N , lower voltage
protection level U P , etc.) than required for lightning protection Probabilities of damage in case of nearby lightning
level I at the relevant places of installation (see Table A.3 of strikes
IEC 62305-1 (EN 62305-1) for information on the current car- The probability P M that a lightning strike near a structure will
rying capabilities, Annex E of IEC 62305-1 (EN 62305-1) and cause failure of internal systems in the structure depends on
Annex D of IEC 62305-4 (EN 62305-4) for lightning current the protection measures taken for the electrical and electronic

Additional protection measures P TA
No protection measures 1
Warning notices 10 -1
Electrical insulation (e.g. at least 3 mm cross-linked polyethylene) of exposed parts (e.g. down conductors) 10 -2
Effective potential control in the ground 10 -2
Physical restrictions or building framework used as down conductor 0
Table 3.2.4.1 Values of probability P TA that a lightning strike to a structure will cause electric shock to living beings due to dangerous touch
and step voltages

Properties of the structure Class of LPS P B
Structure is not protected by an LPS – 1
IV 0.2
III 0.1
Structure is protected by an LPS
II 0.05
I 0.02
Structure with an air-termination system conforming to class of LPS I and a continuous metal (or reinforced con- 0.01
crete) framework acting as a natural down-conductor system
Structure with a metal roof and an air-termination system, possibly including natural components, with complete
protection of any roof installations against direct lightning strikes and a continuous metal (or reinforced concrete 0.001
framework) acting as a natural down-conductor system
Table 3.2.4.2 Probability of damage P B describing the protection measures against physical damage

LPL P SPD
No coordinated SPD system 1
III – IV 0.05
II 0.02
I 0.01
Surge protective devices with better protection characteristics than required for LPL I
(higher lightning current carrying capability, lower voltage protection level, etc.) 0.005 – 0.001
Table 3.2.4.3 Probability of damage P SPD describing the protection measure “coordinated surge protection” depending on the lightning
protection level (LPL)

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