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fore, it is necessary to establish equipotential bonding for all
exposed conductive parts in the building and all extraneous air-termination
conductive parts entering the building. If this is disregarded, system Î
dangerous touch voltages may occur in case of a lightning
strike. down conductor
The rise in potential of the earth-termination system as a re-
sult of the lightning current also creates a hazard for electrical
installations (Figure 2.2.4). In the example shown, the opera-
tional earth of the low-voltage supply system is located outside
the potential gradient area caused by the lightning current. If
lightning strikes the building, the potential of the operational
earth R B is therefore not identical with the earth potential of Û
the consumer’s installation inside the building. In the example, earth-termination system remote earth
the difference is 1000 kV. This endangers the insulation of the with earth resistance R E
electrical installation and the equipment connected to it.
lightning impulse current
ϕ potential relative to ϕ
the reference point current Î
r distance from
the point of strike
time
Figure 2.2.3 Potential rise of the building’s earth-termination system
with respect to the remote earth caused by the peak value
of the lightning current

secondary substation I = 100 kA
r
Figure 2.2.1 Potential distribution in case of a lightning strike to PEN
homogenous ground L1 L2 L3

R E = 10 Ω
R B U E

1000 kV
U E

distance r

Figure 2.2.2 Animals killed by electric shock due to step voltage Figure 2.2.4 Risk for electrical installations resulting from a poten-
tial rise of the earth-termination system

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