According IEC
62305, lightning strikes are simu-
lated with lightning surge currents
of 200 (10/350 μs). The partial light-
ning current then divides itself among the power lines
entering the building (number cores power line
entering building), while around enters data
cables.
The voltage drop the earthing resistor calculated
from the product the partial lightning current (i) and
the earthing resistance (R).3.1 Lightning discharges
(LEMP: Lightning Electro Magnetic Impulse)
The international lightning protection standard IEC
62305 describes how direct lightning strikes to
200 are safely arrested. Even from
several hundred metres away, lightning currents can
also cause impermissible surge voltages conductor
loops, through either capacitive, inductive galvanic
coupling.2 Surge protection system for en-
ergy systems
Very large surge voltages are caused mainly light-
ning strikes close energy systems.
Lightning strike 100% Iimp
= max.
The highest surges are caused by
lightning strikes. For further
information types damage (S1–S4) see Chapter
1. Switching operations involving in-
ductive loads create dangerous surge voltages the
medium and low-voltage power networks. 200 (IEC 62305)
Earthing system 50% 100 (50%)
Electrical installation 50% 100 (50%)
Data cable (5%)
Typical distribution lightning current
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Chapter The internal lightning protection system
.2. This then the potential
difference between the local earth (equipotential bond-
ing) and the active cables, which are earthed some
distance away. Large surge voltages are coupled over ra-
dius km.3 (starts 15).
3. The current coupled in-
to the earthing system and, due the voltage drop at
the earthing resistor, half the lightning current is
coupled into the internal installation
