Explanation of symbols for grounding systems

The international classification of earthing systems is indicated by capital letters. The first letter indicates the nature of the grounding of the power source, and the second - the nature of the grounding of open parts of the electrical installation.

The first letter is the state of the supply neutral to ground:

• T — grounded neutral, direct connection of the neutral of the power supply to the ground (lat. Terra),

• I — insulated neutral (English insulation).

The second letter is the state of open conductive parts relative to ground:

• T — open conductive parts are grounded, i.e. there is a separate (local) grounding of the power supply and electrical equipment,

• N — the power supply is grounded, and consumers are grounded only through the PEN wire (i.e. Neutral — neutral).

Subsequent (after N) letters — combination in one conductor or separation of the functions of the zero working and zero protective conductor:

• C — the functions of zero protective and zero working conductors are combined in one conductor (PEN conductor), (English combined),

• S — neutral working (N) and neutral protective (PE) conductors are separated (English separated).

Non-phase conductors are named as follows:

• N — zero working (neutral) wire (eng. Neutral),

• PE — protective conductor (earthing conductor, neutral protective conductor, protective conductor of the equipotential bonding system, from English protective earth),

• PEN — combined zero protective and zero working conductors (English Protective Earth and Neutral). PEN and its elements are International Electrotechnical Commission (IEC) standards.

Examples of the use of grounding system designations in diagrams.

Isolated neutral system TO:

System with earthed neutral CT:

Here: T (first letter) — grounded neutral, direct connection of the neutral of the power supply to the ground, T — open conductive parts are grounded, that is, there is a separate (local) grounding of the power supply and electrical equipment, I — isolated neutral.

Protective earthing system TN-S:

Here: T — grounded neutral, direct connection of the neutral of the power supply to the ground, N — the power supply is grounded, and consumers are grounded only through the PEN -conductor, S — neutral working (N) and neutral protective (PE) conductors are separated.

Grounding protection system TN-C:

Protective earthing system TN-C-S: