Page 160 - Electrical Safety of Low Voltage Systems

CHAPTER8

Protective Multiple

Earthing (TN-C-S

Grounding System)

Marking dynamos for repair $10,000.00,
2 hours labor $10.00
knowing where to mark $9,990.00.
charles p. steinmetz (1865–1923)

8.1 Introduction
The protective multiple earthing (PME) is a TN-C-S system (Fig. 1.5)
employed as the grounding method for low-voltage public supply,
and is in use in several countries of the world, for example, Australia,
Canada, China, Germany, South Africa, Sweden, Switzerland, U.S.A.,
U.K., etc.
The utility supply neutral conductor is solidly grounded at the
source and at intervals along its distribution. At the dwelling unit’s
service entrance, the neutral wire (PEN) is connected to the customer’s
protective conductor (PE) (Fig. 8.1).
In these conditions, the ground-fault currents, arising at the user’s
installation, will basically return to the supply through the distribu-
tor’s neutral conductor, which therefore acts also as a protective con-
ductor and thus designated as PEN.
In PME, the main equipotential bonding conductors (MEBs) of a
building may be subject to currents, even if the installation is switched
off. This is the contribution of other faulty units supplied by the same
neutral network (Fig. 8.2).

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