1. Earthing System Earthing System for : - Electrical Network
- General Building
- Communication Tower
- Industrial Building

2. Earthing System for Network
Two Letter Codes T N, T T, I T
The First letter indicates connection between earth and power supply
T : direct connection of a point with earth
I :no point is connected with earth (Isolation)
The Second Letter indicate connection between earth &electrical device
T :direct connection with earth
N :connection to earth via the supply network

3. T N network TN Transformer star point is connected with earth
PE protective earth

4. TT network
TT earthing system, the protective earth connection of the consumer is provided by a local connection to earth, independent of any earth connection at the generator

5. IT network
IT network, the distribution system has no connection to earth at all, or it has only a high impedance connection. In such systems an insulation monitoring device used to monitor the impedance.

6. Earthing Design Consideration
A correctly designed and installed earthing system will safeguard both lives and equipment. A good earth connection should have:
-Low electrical resistance to earth
-Good corrosion resistance
-Ability to carry the required current repeatedly
-A reliable life of at least 30 years
The crucial factors that determine the resistance to earth of an electrode are:
- Soil resistivity
- Electrode dimensions
- Area available
- Earth electrode materials

7. Soil Resistivity Soil type Typical resistivity Ohm-m
Effect of soil type on resistivity
Soil type Typical resistivity Ohm-m
Marshy ground Loam and clay Chalk Sand , Peat upwards Sandy gravel
Rock ,000 upwards

8. Earthing System for Tower Radial System

9. Electrodes

10. Ring System 12 meter between loops

11. Earthing Testing
Resistance must be less than 5 ohm in general building
Resistance must be less than 2 ohm in hospitals & clinic building
Resistance must be less than 0.5 ohm in electronic equipments