Page 136 - Electrical Safety of Low Voltage Systems
P. 136
TN Grounding System 119
FIGURE 7.2 Ground fault toward an EXCP not bonded to the grounding system
in TN-S.
The earth connection is an important requirement in TN systems, as
upon its loss users would be exposed to the risk of electric shock
(Fig. 7.3).
At the occurrence of a fault to earth, such as a fault toward a
grounded metal structural element, the current cannot reclose to the
source if the system is not earthed, therefore, protective devices cannot
clear the fault. Persons touching any ECP, even if healthy, may then
become the return path to the fault current, with risk of electrocution.
In Chap. 9, we will discuss the issues with ungrounded systems and
the related safety requirements.
FIGURE 7.3 Risk of electric shock in the absence of the earth connection in
TN system.
