I think I get your question. In European systems the grounding systems are classified as TT, IT and TN systems.
In accordance with IEC 364-4-41 a low voltage distribution system is usually characterized from electricity source to terminal equipment with the following:
i)grounded power supply source (e.g. low voltage connection of local network transformer);
ii)grounded system of exposed conductible parts in consumer electrical installations.
Through this three basic types of systems could be defined as distribution systems:
- TN system;
- TT system;
- IT system.
Used abbreviations have the following meaning:
The first letter describes grounded system of power-feeding electricity source.
T – direct grounding of power supply source single point (primarily connecting point of transformer winding);
I – isolation of all active parts from ground or connection electricity source single point to ground over some sort of impedance.
The second letter describes grounded system of exposed conductible parts of electrical installation
T – exposed conductible part is directly grounded independently of eventual existing grounded feeding point
N – exposed conductible part is directly connected to grounding electrode (grounding resistor)
Further letters describe an arrangement of neutral and protective conductor
S – neutral and protective conductor are separated
C – neutral and protective conductor are connected
Hence it follows that there are three possible varieties of TN system: TN-S, TN-C and TN-C-S
For a diagrammatic representation you may refer to the following website.
Hope the above helps.