Types and kinds of supply networks

Low-voltage power supply networks can be:

  • earthed or
  • insulated in relation to earth.  

The types of low-voltage supply networks are marked with a string of letters.
First letter indicates the relation between network system and earth:

T – direct connection of one network system neutral point with earth
 

I - all parts being under voltage are insulated from earth or the network system neutral point is connected to earth through a high impedance

Second letter indicates the relation between the earth and the conductive parts which are not under voltage in normal operating conditions:
N - direct connection of accessible conductive parts with earthed neutral point of network system  
 


Example of TN network system (the neutral conductor (N) can be omitted)
Description: Odbiornik - Receiver

T - direct connection of accessible conductive parts (which are subject to protection) with earth, irrespective of the earthing of network system neutral point with PE conductor 
 


Example of TT network
Description: Odbiornik - Receiver


Example of IT network
Description: Odbiornik - Receiver

Third and fourth letters, indicate the system of neutral and protective conductors:
C - one conductor (PEN) fulfills the function of neutral and protective conductors in the entire network system

 


Example of TN-C network
Description: Odbiornik - Receiver
 

S - two separate conductors, connected to each other only in the neutral point of network system, fulfill the function of neutral (N) and protective (PE) conductors in the entire network system  
 


Example of TN-S network
Description: Odbiornik - Receiver

C-S - the function of neutral (N) and protective (PE) conductors is fulfilled by one PEN conductor in one part of the system and by separate (N) and (PE) conductors in the second part of the system



Example of TN-C-S network
Description: Odbiornik - Receiver

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