Page 214 - Electrical Safety of Low Voltage Systems

Earth Electrodes, Protective Conductors 197

Minimum Cross-Sectional Areas
2
for Earthing Conductors (mm )
Mechanically Mechanically
Protected Unprotected
Cu Fe Cu Fe
Protected against corrosion 2.5 10 16 16
Not protected against corrosion 25 25 25 25

TABLE 11.9 Minimum Standard Cross-Sectional Area for Earthing Conductors
Embedded in the Soil

All the aforementioned conductors must be able to be disconnected
individually, but only by means of a tool. This allows both earth resis-
tance tests of the earthing electrode, by isolating the influence of the
EXCPs, and the insulation and continuity tests of the PEs.

11.6 The PEN Conductor
As already substantiated in Chap. 7 for TN-C systems, PEN conduc-
tors provide both functions of neutral and protective conductor. The
accidental interruption of the PEN, when the line conductors are live,
energizes the equipment, even if healthy; therefore, its electrical and
mechanical continuity must be guaranteed. To this purpose, the PEN
should only be used in a fixed installation and have a cross-sectional
2
2
area not less than 10 mm in copper or 16 mm in aluminum. These
conditions limit the probability of its accidental interruption.
In some point of the installation, the PEN conductor may split
and originate distinct wires as neutral and PE. The system becomes
TN-S and separate bus bars for the neutral wire and the PE may be
employed (Fig. 11.9).
In the presence of two bus bars, it is safer to connect the PEN to
the PE’s bus bar and not to the neutral one, even though there is no
electrical difference between the two. This arrangement elevates the

FIGURE 11.9
Separate bus bars
for neutral and PE.