Types of Earthing Systems


1.TT Network
2. IT Network
3. TN Network
3.1 TN-S
3.2 TN-C
3.3 TN-C-S
According to IEC 60364 :
1.The first letter: "T" & "I" :

indicates the connection between the earth and the supply generator or transformer

"T" Direct connection of a point with earth
"I" No point is connected with the earth
2.The second letter "T" & "N" :
indicates the connection between the earth or network and the electrical device being supplied
"T" Earth connection is by a local direct connection to earth usually via a ground rod.
"N" the earth connection is supplied by the electricity supply network, either separately to the neutral conductor (TN-S), combined with the neutral conductor (TN-C), or both (TN-C-S).


1.TT Network


First letter T means the neutral is connected to the earth
The second letter T means the machine enclosure is connected to the earth
In a TT earthing system, the protective earth connection for the consumer is provided by a local earth electrode, and there is another independently installed at the generator.
Supply (generator or transformer) and the load connected through earth resistance but There is no earth wire between the two.
-TT earthing system is always preferable for special applications like telecommunication sites.
-TT networks do not pose any serious risks in the case of a broken neutral.
-TT is recommended for situations where a low impedance equipotential zone is impractical to maintain by bonding such as agriculture areas or where a high fault current could pose other dangers, such as at fuel stations.
-The TT earthing system is used with ground fault circuit interrupter GFCI units in most industrial settings.
-TT system is simple in design, installation, and reliable


2.IT Network




In an IT network, the electrical distribution system has no connection to the earth at all, or it has only a high impedance connection.
the first letter I mean neutral not connected to the earth.
the second letter means the load insulation is connected to the earth.
In case of leakage current and insulation failure no leakage current path from machine insulation to the neutral.
-No risk of broken neutral
-installing GFCI is not required
-IT earthing system is the best solution for continuity of operation


3.TN Network


In a TN earthing system
letter T mean the neutral in the generator or transformer is connected with the earth in a three-phase system.
letter N means the enclosure of the electrical device is connected with the earth via this earth connection at the transformer.
The conductor that connects the exposed metallic parts of the electric machine installed is called protective earth (PE).

- TN−C
A Combined PEN conductor fulfills the functions of both a PE and an N conductor.
installing GFCI is not required.

- TN−C−S

Part of the system uses a Combined PEN conductor, which is at some point split up into Separate PE and N lines.
The combined PEN conductor typically occurs between the substation and the entry point into the building, and earth and neutral are separated in the service head
installing GFCI is optional


- TN−S


Protective earth PE and N are Separate conductors that are connected together only near the power source.
installing GFCI is optional
.


Main Component Parts of The Earthing System:

The earthing system is the basis for the safe function of every electrical system. It ensures operation and protects people against hazardous currents.
components of the earthing system:
1.earthing conductor
The body of the electric machine is connected to the earth through protective earth conductor such as a TT system.
2.earthing electrode
earth conductor is connected to earth through electrodes and electrodes are immersed inside the soil.
A foundation earth electrode is a closed ring, ideally consisting of flat conductors or, alternatively, of round conductors, with a maximum grid width of 20 x 20 m.
The foundation earth electrode is connected to the reinforcement at a spacing of approximately 2 m using clamping connectors.
To ensure corrosion protection, the foundation earth electrode must be embedded in the concrete with a jacket of at least 5 cm.
The concrete sets up the electrical connection between the foundation earth electrode and the earth.
3.soil
The type of soil is an important factor that affects earth resistance such as ( clay, sand, limestone ) each type has different resistivity.
to decrease earth resistance increase:
1.the amount of salt inside soil because salt increase conductivity.
2.moisture percentage in the soil.
that's why Wet soil has a lower resistivity than dry soil.
4.temperature of the soil decrease resistivity of the soil.
5.increase depth of soil decrease resistivity.
6.increase the number of electrodes because electrodes are connected in parallel.