EARTHING SYSTEM/GROUNDING SYSTEM SIMPLIFIED
EARTHING SYSTEM/GROUNDING SYSTEM
Earthing system or grounding system connect all exposed conductive parts of an electrical installation to a point reference normally earthing terminal of a system by means of protective earth conductor for safety and functional reason.
The main earthing terminal is connected to the earth rod which is specifically located outside the building.
Bonding and earthing are two terms most of us confuse and come often when discussing one of them. So;
Electrical bonding is a practice of connecting all metallic solid parts together that maybe exposed to electric faults to reduce risk for electric shock.
Earthing must be done in all buildings and they should be in accordance to you country standards which varies depending on the type of earthing system implemented. And also in accordance with the Institute of Electrical and Electronics Engineers (IEEE).
Objectives of earthing/grounding system
Methods of grounding system.
There are two different methods of grounding system
1.?????Earthed system
2.?????Unearthed or Insulated system
The main difference between the two is; For the earthed system, the neutral of the system is connected to the earth using conducting electrode while for the unearth system, it has no connection to the earth. Phone is one of the example of application of unearth system.
The three types of earthing/grounding system
Earthing system has nomenclature used to distinguish the three families, according to international standard IEC 60364.
F The first letter represents the connection between the earth and power supply.
‘T’- Neutral point of the power supply is directly connected to the earth using earthing rod?(French: terre).
‘I’ – There is no connection between the earth and the neutral point of power supply (French: isolé).
F The second letter represents the connection between the earth and electrical consumer’s installation.
‘T’- Earthing rod directly connects to the earth.
‘N’- Connection to the earth is supplied by power supply network.
F The subsequent letter representation represents how the neutral and earth conductor is arranged distribution system.
‘C’- The protective function of the conductor in the form of neutral are combined in single conductor
‘S’-The protective function of the conductor is provided by earth conductor is e separate from neutral conductor.
‘PE’- Protective earth conductor
Here are the three types of earthing system.
1.?????TT system
2.?????IT system
3.?????TN system
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1. TT earthing system?(French: terre-terre)
TT earthing system has both power supply and consumer installation connected directly to the earth using the earth electrode.
The power distributor only provides the consumer with the neutral and live connections without the earthing connection.
The power distributor only provides the consumer with live and neutral connections. Consumers will install their own independent earthing connection to safeguard their devices. Therefore, the earth and the neutral wire are separate from each other.
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It is used in temporary distribution where the distributor does not guarantee the consumer with a low voltage back to the supply.
This type of earthing is mostly used in construction sites, mining sites, and in rural areas where the distributor does not guarantee the consumer with low voltage back to the supply. Also, it is commonly used in the telecommunication because has an interference free earthing.
TT systems has high fault loop impedance therefore it must have RCDs-Residual Current Devices to protect the installed devises.
2. IT earthing system (French: isolé-terre)
In IT earthing system, the distribution system does not have earth connection and instead, it has a high impedance connection to the earth. In the scenario where there is fault connection, power will not be interrupted. This make an ideal earthing system for use in areas that require safety critical care such as intensive care units or railway signaling technology and power substation distribution.
3. TN earthing system
TN earthing system involves connection of one main point in the source of power such as generator to the earth electrode. A protective earth conductor is used to connect all exposed metallic parts of the installation to that main point.
In three phase system, the neutral conductor is used as the main point to connect star point of the system.
In single phase, the neutral conductor acts as return path for the current.
Three Variants of TN earthing system
Depending on the way Protective Earth (PE) and Neutral(N) conductors are interconnected in the system, we get the three variants
The protective earth(PE) and neutral(N) conductors are separate throughout the distribution system and are only connected at the power supply where they tap the protective conductor form neutral wire..
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The protective earth conductor and the neutral are combined to a single conductor call PEN throughout the system. Metallic parts exposed in the installation are connected to PEN. The figure below illustrates it.
In this the PE and N conductors are combined in one part of the utilizing the TN-C system mainy between the substation and entry into the building and at some point it is separate, therefore uses the TN-S at the service heads.
Conclusion
Safety of the consumers is the most important factor while installing the any type of the earthing system. The other factor is safety of devices used in the installation. Depending on the area where it is used, some factors will be considered of higher consideration than others.
The above article should be a refreshing introduction to power system.
Comment below for clarity and questions that you might be having about earthing system.
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References