Page 78 - Electrical Safety of Low Voltage Systems

The Earth 61

FIGURE 4.18 Person standing in an area at zero potential, while touching a
faulted enclosure (worst-case scenario).

of the area occupied by the person’s feet (i.e., at distance L from the
electrode’s surface). The ground potential rises from zero to V BG =
R BG I B , as shown in Fig. 4.18.
A better-case scenario for safety occurs when the person is stand-
ing in an area at nonzero potential at a distance l < L from the elec-
trode (Fig. 4.20).
The perspective touch voltage V ST is less than the earth potential
V G and, in addition, the presence of the person rises the potential
under his/her feet.

FIGURE 4.19
Equivalent fault-loop
for a person standing
in an area at zero
potential.