Page 166 - Electrical Safety of Low Voltage Systems

Protective Multiple Earthing (TN-C-S Grounding System) 149

FIGURE 8.7 Distinct grounds at the utility transformer.

This strategy, although effective for the customers, is not free of
risk for the utility’s operators engaged in maintenance activity within
the substation. The PEN conductor, in fact, becomes an EXCP, liable
to introduce a “zero” potential or a fault potential into the premises.
With this arrangement, workers must take precautions and treat the
PEN as a “live” conductor.

8.2.3 Faults Phase-to-PEN in Low-Voltage PME Networks
Another cause of energization of the PEN conductor may be the ac-
cidental contact with the phase conductor in low-voltage distribution
networks (Fig. 8.8).
The resulting short circuit causes a circulation of current back to
the source through the PEN conductor. We assume to neglect the fault
current derived by the EXCPs at the user’s location, connected for

FIGURE 8.8 Short circuit phase-to-PEN in PME.