- Function,
- System size,
- Neutral point connection to earth (Neutral Grounding),
- Neutral point connection to earth(Neutral Grounding) + the connection method of the electrical installations exposed conductive parts (Frame Grounding).
And I explained the first two categories in this Article, showing that:
- Types of Earthing Systems according to its Function can be divided to Six types as follows:
- Static grounding,
- Equipment grounding,
- System grounding,
- Lightning grounding,
- Electronic (including computer) grounding,
- Maintenance safety grounding.
- And Types of Earthing Systems according To Its Size can be divided to Two types as follows:
- simple.
- complex.
You can preview the following Articles for more info:
Types of Earthing System (on LV Systems and Within Premises)
Different Types Of Earthing Systems
the Earthing systems can be divided according to
the following factors:
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Types Of Earthing Systems According
To Neutral Point Connection To Earth (Neutral Grounding)
The Earthing systems can be divided to Five Types
according to neutral point connection to earth as follows:
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Types of Neutral Point Connection
To Earth
1- Solidly earthed neutral
An electrical connection is intentionally made
between the neutral point and earth.
2- Unearthed neutral
There is no electrical connection between the
neutral point and earth, except for measuring and protective devices.
3- High impedance earthing
A high impedance is inserted between the
neutral point and earth.
4- Resistance earthing
A resistor is inserted between the neutral
point and earth.
5- Reactance earthing
A reactor is inserted between the neutral point
and earth.
6- Petersen coil earthing
A reactor tuned to the network capacitances is
inserted between the neutral point and earth so that if an earth fault
occurs, the fault current is zero.
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Comparison between Neutral
Grounding Methods
The performance characteristics of each
neutral grounding method discussed above
can be compared as in below table:
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Types Of Earthing Systems According
To Neutral Point Connection To Earth + The Connection Method Of The
Electrical Installations Exposed Conductive Parts.
According to Neutral point connection to earth + the
connection method of the electrical installations exposed conductive parts, The
Earthing systems can be divided to Five schemes as follows:
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(3) Main Earthing Schemes
Each one of the 3 Main Types is defined by two
letters as follows:
The First Letter:
It defines the situation of the neutral point
in relation to earth, like:
T : solidly earthed neutral
I: unearthed or high impedance earthed neutral.
The Second Letter:
It defines the connection method of the electrical
installation's exposed conductive parts, like:
T : the exposed conductive parts are
interconnected and solidly earthed, regardless of whether the neutral point
is earthed or not
N: the exposed conductive parts are directly
connected to the neutral conductor.
So the three main earthing systems will be:
IT (Unearthed transformer neutral, earthed frame),
TT (Transformer neutral earthed, and frame earthed),
TN (Transformer neutral earthed, frame connected to
neutral).
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(3) Sub-Main Earthing Schemes
The Three sub-main earthing system are derived
from the main TN earthing system as
follows:
TNC (If the N and PE neutral conductors are one and
the same (PEN))
TNS (If the N and PE neutral conductors are separate),
TNC-S (Use of a TN-S downstream from a TN-C (the
opposite is forbidden).
Where:
C : N and PE Combined,
S : N and PE Separate,
PEN: (Protective Earth and Neutral)
conductor.
Note:
Each system earthing can be applied to an
entire LV electrical installation; however several system earthings may be
included in the same installation.
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IT earthing system
First letter I:
The neutral is unearthed or earthed via a high
impedance, An impedance between 1000 and 2000 Ω is frequently used.
Second letter T:
The exposed conductive parts of loads are
interconnected, either altogether, or in groups. Each interconnected group is
connected to an earth electrode. It is possible for one or several exposed
conductive parts to be separately earthed.
Notes:
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TT earthing system
First letter T:
The neutral point is directly earthed.
Second letter T:
The exposed conductive parts of the loads are
interconnected, either altogether, or in groups, or individually, and are
earthed. Protection is ensured by residual current devices. All the exposed
conductive parts protected by the same protective device must be connected to
the same earth electrode.
Note:
The neutral earth electrode and that of the
exposed conductive parts may or may not be interconnected or the same. The
neutral may or may not be distributed.
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TN earthing system
First letter T:
The neutral point is directly earthed.
Second letter N:
The exposed conductive parts of the loads are
connected to the neutral conductor.
the TN earthing system can be divided to 3 sub-main earthing schemes as follows:
1- TNC earthing system
Third letter C:
The neutral and protective conductors form a
single conductor called the PEN.
Notes:
2- TNS earthing system
Third letter S: The neutral conductor and protective conductor are separate.
3- TNC-S earthing system
In TNC-S earthing system, both TNC and TNS earthing systems can be used in
the same installation. But the TNC earthing system (4 wires) must
never be downstream of the TNS earthing system (5 wires).
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In the next Article, I will explain the Selection Criteria for the Best Earthing System. Please, keep following.
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