In building installations, grid systems are important for the safety and efficiency of electrical systems. The different grid systems, TT, IT, TN-C, TN-C-S and TN-S systems, offer different approaches to earthing and residual current discharge. Each of these grid systems has specific applications as well as advantages and disadvantages that must be taken into account during planning and installation.
The grid is divided into a transmission grid and a distribution grid.
The transmission grid comprises the extra-high and high-voltage grids and the distribution grids are in the medium and low-voltage range.
The international standard IEC 60364 differentiate between three groups of earthing arrangements with the letter codes TN, TT and IT.
First letter | Second letter | Third letter |
| Earthing at current source | Earth connections of the devices | Use of Neutral and PE |
| T Direct earthing of current source (Star point) | T Device direct earth, independent from the earthing and power device | C Neutral and PE are combination with one wire |
| I Insulated structure | N Device is direct connected to standard earth | S Neutral and PE are used separate |
Grid voltage is the electrical voltage provided by the energy suppliers in the electricity grids that is used to transmit electrical energy. In a narrower sense, grid voltage is often understood to be the level of alternating voltage in low-voltage grids.
