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struction has the advantage that this connection is mechani-
cally highly stable, electrically safe and capable of carrying
lightning currents during the drive-in process.
¨ With an earth electrode of type S, the soft metal in the
borehole deforms during the drive-in process, creating an
excellent electrical and mechanical connection.
¨ With an earth electrode of type Z, the high coupling quality
is achieved by means of a multiply knurled pin.
¨ With an earth electrode of type AZ, the high coupling qual-
HES
ity is achieved by means of an offset multiply knurled pin.
Different striking tools are used to drive the earth rods into
the ground. When selecting these tools, it must be observed
Figure 5.5.3.1 Ring earth electrode around a residential building that the earth rod is driven into the ground with approximately
1200 strokes/min. A significantly higher number of strokes is
not advisable, since the striking energy is often not sufficient
the earth electrode must be installed in such a way that they
are in contact with the soil. If this is not possible, it has to be to drive the earth rod deep enough into the ground. In case of
checked if additional type A earth electrodes are required. striking tools whose striking frequency is too low as is the case
with pneumatic tools, the striking power is much too high and
The requirements on the minimum earth electrode length must the number of strokes is too low. The weight of the striking tool
be taken into account depending on the class of LPS (see chap- should not exceed 20 kg.
ter 5.5.1). When installing the ring earth electrode, it must be The penetration depth of earth rods depends on various geo-
also observed that it is buried at a depth > 0.5 m and 1 m logical conditions. In light grounds, which can be found for
away from the building. If the earth electrode is driven into the example in coastal areas or wetlands, penetration depths
soil as described before, it reduces the step voltage and thus between 30 m to 40 m are possible. Where extremely hard
controls the potential around the building. grounds are encountered, for example in natural sandy
ground, penetration depths of more than 12 m are frequently
This ring earth electrode should be installed in natural soil. If it impractical. If conventional earth rods are used, the soil is not
is installed in backfill or soil filled with construction waste, the drilled out during the drive-in process, but pushed away by the
earth resistance is reduced. earth rod. This compresses the soil around the earth electrode
When choosing the earth electrode material with regard to and ensures good electrical contact with the surroundings. The
corrosion, local conditions must be taken into consideration. It larger the outer diameter of the earth rod, the more soil is
is advisable to use stainless steel. This earth electrode material pushed away. For heavy grounds, for example, an earth rod
does neither corrode nor subsequently require time-consuming with an outer diameter of 25 mm is optimal with regard to
and expensive reconstruction measures for the earth-termina- the maximum drive-in depth and the soil pushed away by the
tion system such as removal of paving stones, tar surfaces or earth electrode.
even steps for installing a new earthing material. To drive earth rods into greater depths (penetration depths
In addition, the terminal lugs must be particularly protected > 6 m), it is recommended to use a hammer frame (Part No.
against corrosion.

5.5.4 Earth rods – Type A earth electrodes Type S
The sectional DEHN earth rods are made of special steel and
are hot-dip galvanised or consist of high-alloy stainless steel
(V4A), e.g. material No. AISI/ASTM 316 Ti. These earth rods are Type Z
characterised by their self-closing coupling joint, which allows
the earth rods to be connected without increasing their diam-
eter. Type AZ
Each rod has a borehole at its lower end, while the other end
of the rod has a corresponding pin (Figure 5.5.4.1). This con- Figure 5.5.4.1 Couplings of DEHN earth rods

140 LIGHTNING PROTECTION GUIDE www.dehn-international.com