Understanding the IEC Standards for Earthing Systems

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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