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

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

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

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

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.

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

Soil Resistivity Soil type Typical resistivity Ohm-m Effect of soil type on resistivity Soil type Typical resistivity Ohm-m Marshy ground 2.7 Loam and clay 150 Chalk 400 Sand 8,000 Peat 200 upwards Sandy gravel 500 Rock 1,000 upwards

Earthing System for Tower Radial System

Electrodes

Ring System 12 meter between loops

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