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An electrical isolation of parts of an installation acting as an-
odes to prevent this cell formation is only possible in excep- Copper rod with hole
tional cases. Today the aim is to interconnect all earth elec- for measurements
trodes also with other metal installations in contact with the Rubber plug
soil to establish equipotential bonding and thus ensure maxi-
mum safety against excessive touch voltages in the event of a Ceramic cylinder with porous base
fault and lightning effects. Glaze
In high-voltage installations, high-voltage protective earth
electrodes are increasingly connected to low-voltage op- Saturated Cu/CuSO 4 solution
erational earth electrodes in accordance with IEC 60364 Cu/CuSO 4 crystals
(EN 60364). IEC 60364-4-41 (HD 60364-4-41) / IEC 60364-5-54
(HD 60364-5-54) requires to integrate pipework and other in-
stallations in the protection measures against electric shock. Figure 5.5.7.1.1 Application example of a non-polarisable measuring
electrode (copper / copper sulphate electrode) for
Thus, the only way of preventing or at least reducing the risk tapping a potential within the electrolyte (cross-
of corrosion for earth electrodes and other installations con- sectional view)
nected to them is to choose suitable earth electrode materials.
In Germany, the national DIN VDE 0151 standard “Material
and minimum dimensions of earth electrodes with respect to Reference electrode
corrosion” is available since June 1986. Apart from decades of is a measuring electrode for determining the potential of a
experience in the field of earthing technology, the results of metal in the electrolyte.
extensive preliminary examinations have also been included in
this standard. The fundamental processes leading to corrosion Copper sulphate electrode
are explained below. Practical anti-corrosion measures espe- is an almost non-polarised reference electrode consisting of
cially for lightning protection earth electrodes can be derived copper in a saturated copper sulphate solution.
from this and from the material prepared by the VDE task force The copper sulphate electrode is the most common reference
on “Earth electrode materials”. electrode for measuring the potential of buried metal objects
(Figure 5.5.7.1.1).
Terms used in connection with corrosion
protection and anti-corrosion measurements Corrosion cell
Corrosion is a galvanic cell with locally different partial current densities
is the reaction of a metal material with its environment which for dissolving the metal. Anodes and cathodes of the corrosion
impairs the characteristics of the metal material and / or its en- cell can be formed:
vironment. In most cases, the reaction is electrochemical.
¨ on the material
Electrochemical corrosion due to different metals (contact corrosion) or different
is corrosion during which electrochemical processes occur. structural constituents (selective or intercrystalline corro-
They only take place in the presence of an electrolyte. sion).
¨ on the electrolyte
Electrolyte due to different concentrations of certain substances with
is an ion-conducting corrodent (e.g. soil, water, molten salt). stimulating or inhibitory characteristics for dissolving the
metal.
Electrode
is an electron-conducting material in an electrolyte. The elec- Potentials
trode and electrolyte form a half-cell.
¨ Reference potential
potential of a reference electrode with respect to the stand-
Anode
electrode from which direct current passes into the electrolyte. ard hydrogen electrode.
¨ Electrical potential
Cathode is the electrical potential of a metal or an electron-conduct-
electrode which absorbs direct current from the electrolyte. ing solid in an electrolyte.

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