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If ring earth electrodes (control earth electrodes) cannot be (e.g. shelters), measures against impermissibly high touch
installed as a circle, their ends must be connected to the other voltages may also be required. In addition, the risk to per-
ends of the ring earth electrodes. There should be at least two sons is included in a risk analysis for a structure according to
connections within the individual rings (Figure 5.7.5). IEC 62305-2 (EN 62305-2) in the form of the parameter L1
(injury or death of persons).
When choosing the materials for the ring earth electrodes, pos-
sible corrosion must be observed (chapter 5.5.7). The following measures reduce the risk of touch voltage:

Stainless steel (V4A), e.g. material No. AISI/ASTM 316 Ti, has ¨ The down conductor is covered with insulating material (at
proven to be a good choice when the cell formation between least 3 mm cross-linked polyethylene with an impulse with-
the foundation and ring earth electrode is taken into account. stand voltage of 100 kV (1.2/50 µs)).
Ring earth electrodes can be designed as round wires ¨ The position of the down conductors is changed (e.g. no
(Ø 10 mm) or flat strips (30 mm x 3.5 mm). down conductors in the entrance area of the structure).
¨ The resistivity of the surface layer of the earth within up
to 3 m around the down conductor is at least 100 kΩ
5.7.1 Coping with touch voltage at the down (IEC 62305-3 (EN 62305-3)).
conductors of a lightning protection
system ¨ The probability of persons accumulating can be reduced by
The area at risk of touch and step voltages for persons outside notes or prohibition signs. Barriers are also a possibility.
a building is located within a distance of 3 m around the build- Protection measures against touch voltage are not always
ing and at a height of 3 m. The height of this area is equal to
the height of the maximum reachable height of a person rais- sufficient to ensure effective personal protection. For exam-
ing a hand and an additional separation distance s (Figure ple, it is not sufficient to cover an exposed down conductor
5.7.1.1). with a high-voltage-resistant insulation if protection measures
against creeping flashover at the surface of the insulation are
Special requirements apply to protection measures in e.g. not taken at the same time. This is particularly important if
entrance areas or covered areas of highly frequented struc- environmental influences such as rain (moisture) must be con-
tures such as theatres, cinemas, shopping centres and nursery sidered.
schools for which no insulated down conductors and lightning As is the case with bare down conductors, a high voltage builds
protection earth electrodes are in close proximity. up in the event of a lightning strike if insulated down conduc-
In case of extremely exposed structures (structures prone to tors are used. However, the insulation protects persons from
lightning strikes) which are accessible to the general public this voltage. Since it can be assumed that the human body is
extremely conductive compared to the insulating material, the
insulation layer is loaded with almost the total touch voltage.
If the insulation does not withstand this voltage, a part of the
s
lightning current can travel through the human body to earth
as is the case with bare down conductors. To ensure that per-
sons are reliably protected against touch voltage, it is therefore

PEX insulation

2.50 m
copper conductor

PE sheath

Figure 5.7.1.1 Area to be protected for a person Figure 5.7.1.2 Design of a CUI Conductor

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