Page 173 - Electrical Safety of Low Voltage Systems

156 Chapter Nine

FIGURE 9.1 Ground-fault currents circulating through the system capacitance
to ground.

The current circulating after the first fault, thus, is mainly capacitive.
In the case of indirect contact with a faulty ECP, therefore, persons
are exposed to the risk of electrocution (Fig. 9.1). C 0 increases with
the cables’ extension and so does the ground-fault current flowing
through the person. Such current, relatively small in absolute value
(i.e., tens of amperes), are large enough to be lethal to persons. To
avoid this hazard, the ECPs must be earthed, as previously anticipated
(Fig. 9.2).

FIGURE 9.2 Earth current flowing through the ECPs ground and the capacitive
system impedance to ground.