Earthing is a safety precaution that involves connecting an electrical system to the surface of the ground. It allows electrical current to pass safely to ground in the event of a fault or overload, lowering the risk of electrocution, fire, & equipment damage.
The International standard IEC 60364 defines 3 types of earthing arrangements:
1). TN
2). TT
3). IT
- The first letter shows how the earthing is done on the source side (generator/transformer).
- The Second Letter specifies how the Earthing is done on the device side.
- ‘T’ indicates that direct connection of a point to the ground.
- ‘I’ indicates that either no point is linked to Earth (or) it is connected via a high impedance.
- ‘N’ indicates that there is a direct connection to neutral at source of installation, which is then connected to the ground.
1). TN Earthing System
- Three types of TN earthing systems exist, according on how the neutral & protective conductors are fed.
- The TN-S system makes use of a separate protecting conductor.
- TN-C-S system: The neutral & protective conductors are merged into a single conductor in a system component.
- TN-C system: The neutral & protecting conductors are integrated into a single conductor in the entire system.
2). TT Earthing System
- The neutral is directly earthed on the source side.
- The consumer is powered via a local earth electrode.
3). IT Earthing System
- The power supply is either not earthed (or) earthed with a high impedance.
- The exposed conductive portions of the system are connected to ground independently of the power source.
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