Question/Comment:
In which context?
IT, as it appears in news media and technical publications, often nowadays stands for "Information Technology". See IEEE Std 100-2000 "Dictionary"
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.
In short , the IT System is such that the neutral is unearthed. All exposed-conductive-parts of the installation are connected to independent grounding electrodes. When there is a great need of continuance and maintainence of service this type of a earthing system is chosen.Since when the first insulation fault occurs there is no risk to the user as the fault voltage is low, not dangerous and the installation can be kept in operation. An SCPD device would be required only in the case of a double fault.
for:
Earthing System IT Earthing system in which the neutral is isolated from the earth or connected to the earth via a high impedance and the various exposed conductive parts are connected to the earth via individual earthing circuits. An alarm must signal the appearance of a first insulation fault. The installation must be de-energized immediately in the event of a second insulation fault.
