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air-termination d Sag of the rolling sphere
conductor r Distance Class of LPS with rolling sphere radius [m]
[m] (rounded up)
penetration depth p the air-ter- (20 m) (30 m) (45 m) (60 m)
between
III
II
IV
I
mination
rods [m]
∆h
0.10
4 2 0.03 0.02 0.01 0.01
0.07
0.03
0.04
6 0.23 0.15 0.10 0.08
d 8 0.40 0.27 0.18 0.13
10 0.64 0.42 0.28 0.21
Figure 5.1.1.7 Penetration depth p of the rolling sphere 12 0.92 0.61 0.40 0.30
14 1.27 0.83 0.55 0.41
16 1.67 1.09 0.72 0.54
Class of LPS 18 2.14 1.38 0.91 0.68
I II III IV 20 2.68 1.72 1.13 0.84
r r 20 30 45 60 23 3.64 2.29 1.49 1.11
26 4.80 2.96 1.92 1.43
29 6.23 3.74 2.40 1.78
32 8.00 4.62 2.94 2.17
35 10.32 5.63 3.54 2.61
d Table 5.1.1.2 Sag of the rolling sphere in case of two air-termina-
p
∆h tion rods or two parallel air-termination conductors
rectangular protected
volume between four
air-termination rods
does not “roll on rails” but “sits deeper” instead, thus increas-
Figure 5.1.1.8 Air-termination system for roof-mounted structures
and their protected volume ing the penetration depth of the sphere (Figure 5.1.1.8).
The height of the air-termination rods Δh must always be
greater than the value of the penetration depth p determined,
and hence greater than the sag of the rolling sphere. This addi-
tional height of the air-termination rod ensures that the rolling
d diagonal sphere does not touch the object to be protected.

Another way of determining the height of the air- termination
rods is to use Table 5.1.1.2. The penetration depth of the
rolling sphere is governed by the largest distance of the air-
termination rods from each other. Using the greatest distance,
the penetration depth p (sag) can be read off from the table.
The air-termination rods must be dimensioned according to the
height of the roof-mounted structures (in relation to the loca-
∆h tion of the air-termination rod) and also the penetration depth
domelight
installed on the roof (Figure 5.1.1.9).
If, for example, a total air-termination rod height of 1.15 m is
Figure 5.1.1.9 Calculation of Δh for several air-termination rods either calculated or obtained from the table, an air-termination
according to the rolling sphere method rod with a standard length of 1.5 m is normally used.

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