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¨ Caused by the first positive stroke:
shield from
LPZ 0 A – 1 I
H 0/f /max = f /max in A/m
safety distance 2 ( s )
a
volume V s direct lightning
for electronic strike:
w devices d s/1 = w ¨ Caused by the first negative stroke:

d s/1 I
H = fn/max in A/m
0/fn/max 2 ( s )
Figure 7.3.3 Volume for electronic devices in LPZ 1 a
¨ Caused by the subsequent strokes:

Determination of the magnetic field in case of a I
nearby lightning strike H = s/max in A/m
The incident magnetic field H 0 is calculated as follows: 0/s/max 2 ( s )
a
I where
H = 0 in A/m I f/max is the maximum value of the first positive stroke
0 2 ( s )
a current in accordance with the LPL in A;
where I fn/max is the maximum value of the first negative stroke
I 0 is the lightning current in LPZ 0 A in A; current in accordance with the LPL in A;
s a is the distance between the point of strike and the I s/max is the maximum value of the subsequent stroke
centre of the shielded volume in m. currents in accordance with the LPL in A.

From this follows for the maximum value of the magnetic field The reduction of H 0 to H 1 inside LPZ 1 can be derived using the
in LPZ 0: SF values given in Table 7.3.1:

H
Shielding factor SF (dB) H = 0/max
Material 25 kHz 1 MHz (subse- 1/max 10 SF/20 in A/m
(first stroke) quent stroke)
where
Copper or
aluminium 20 ∙ log (8.5/w m ) 20 ∙ log (8.5/w m ) SF is the shielding factor determined using the equations
in Table 7.3.1 in dB;
(8.5/w ) H 0 is the magnetic field in LPZ 0 in A/m.
Steel 20 log m 20 ∙ log (8.5/w m )
-6
1+18 10 /r 2
c
From this follows for the maximum value of the magnetic field
w m = mesh size [m] (w m ≤ 5 m); r c = rod radius [m]; in LPZ 1:
µ r ≈ 200 (permeability)
¨ Caused by the first positive stroke:
Example: Steel grid
w m (m) r (m) dB at 25 kHz dB at 1 Mhz H 0/f /max
0.012 0.0010 44 57 H 1/f /max = 10 SF/20 in A/m
0.100 0.0060 37 39
¨ Caused by the first negative stroke:
0.200 0.0090 32 33
0.400 0.0125 26 27 H

Table 7.3.1 Magnetic attenuation of grids in case of a nearby H 1/fn/max = 0/fn/max in A/m
SF/20
lightning strike according to IEC 62305-4 (EN 62305-4) 10

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