Page 112 - Electrical Safety of Low Voltage Systems

CHAPTER6

TT Grounding

System

Electricity, water, gas, and steam course through
the walls of my building, keeping it alive.
mason cooley (1991)

6.1 Introduction
The TT system (Terre-Terre, or earth-earth) is the grounding method
for low-voltage public supply employed in several countries in
the world; for example, Algeria, United Arab Emirates, Belgium,
Denmark, Egypt, France, Greece, Italy, Japan, Kenya, Luxemburg,
Morocco, Tunisia, Spain, Portugal, Turkey, etc.
The supply system is solidly grounded, and the neutral is usually
carried in order to provide power to single-phase loads, as is typical
of dwelling units.
The consumer’s ECPs (exposed-conductive-parts) are connected
to a house ground electrode, independent of the earthing of the utility.
In these conditions, the ground-fault current will return to the supply
through the soil (Fig. 6.1), flowing through both the earth electrode of
the installation (R G ) and the earth electrode of the source (R N ).
As a result, the ground-fault current is limited in its magnitude by
the two above-mentioned grounds, as the impedances of phase and
1
PE conductors are negligible if compared to R G and R N . Therefore, I G
is independent of where the ground fault occurs within the system.
TT grounding systems are used when electrical utilities cannot
make available safe means of earthing for their users. The owner of
the installation, therefore, must provide its own connection to ground,
employing suitable earth electrodes [i.e., conductive element(s) in in-
timate contact with earth].

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