Understanding Type Of Earthing System
T = Terre (French for earth) and meaning a direct connection to earth
N = Neutral
C = Combined
S = Separate
When these letters are grouped together they are form the classification of a type of system.
The first letter in such of classification denotes how the supply source is earthed.
The second denotes how the metalwork of an installation is earthen.
The third and fourth indicate the functions of neutral and protective conductors.
1. A TT System has a direct connection of the supply source to earth and a direct connection of the installation metalwork to earth.
2. A TN-S system has the supply source directly connected to earth and the installation metalwork connected to the earthen neutral of the power supply source via the metal sheath of the supply cable, and the neutral and protective conductor throughout the whole system performing separate functions.
3. A TN-C-S system is at the TN-S system but the supply cable is also the neutral, that is, it forms a combined earth/neutral conductor known a PEN (Protective Earthen Neutral) conductor. The installation earth an neutral are separate conductor. This system is also known as PME (Protective Multiple Earthing).