Earthing System Classification

In electrical wiring and installation,earthing is the important thing that we must make sure it in our job scopes.Earthing system for electrical installation is for the safety and electromagnetic power supply purpose.

Earthing system function is to ensure all equipment or device is safe from risk of electric shock and make sure the residual current device operate properly.

We should decide a suitable types of earthing system for our application and must understand the classification.Earthing system have a several types commonly used in all around the world listed as below :-

  • TT system
  • TN system ( TN-S,TN-C and TN-C-S )
  • IT system

For the more detail about types of earthing system,i explain detail in my post title : Types of Earthing System.This time i want to share about the meaning of the letter that used for types of earthing system codes.


Types of Earthing System classification.

Letter Classification

1) First Letter ( Types of supply earthing )

T : It mean ” one or more the source of power supply is earthed ” e.g : The neutral point of transformer.

I : It mean ” No source of consumer power supply is earthed at all “.The main purpose is to avoid or limit the fault current.

2) Second Letter ( Earthing arrangement )

T : It mean ” all exposed metal conductor connected directly to the general mass of earth ”

I : It mean ” all exposed metal conductors are connected to the earth conductor of the user power supply source ”

3) Third and Fourth Letter ( Arrangement of the earthed supply conductor system )

S : ” Separation system of neutral and earth conductors ”

I : ” Neutral and earth is the combined together for single conductor  ”

This is the terminology from International Standard IEC 60364.For more detail please refer to the standard.


  1. lắp đặt điện lạnh says

    Great article.

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