What is earthing
Earthing can be described as transmitting the immediate discharge of electricity with the help of low resistive wires to the ground. It is a connection to the general mass of the earth by the earth electrode. In this process the metallic bodies of all electrical apparatus will be connected to the earth by a wire which has low resistivity, the neutral point of the supply system or the non-current carrying part of the electrical apparatus will be connected to earth and its advantage is that if an immediate discharge of electrical energy takes place there won’t be any danger. A device is said to be earthed if it is electrically connected to an earth electrode.
What is a solidly earthed system
A device or a system can be said to be solidly earthed if it is electrically connected to an earth electrode without the intention of additional resistance or impedance in earth connection, and this system can protect the device from over-voltages.
What are the objectives of earthing
- It can provide an alternative path for the fault current so the fault current can travel in that path without damaging the equipment or endanger the user
- The conductive parts which are exposed won’t reach a dangerous potential
- Voltage can be maintained in an electrical system by preventing overcurrent and excessive voltages
- Low impedance path will be provided to the fault current and by this, it can ensure the correct operation of protective devices
Why do we need earthing
Earthing is done for the safety of humans, equipment, property and if there is no effective earthing then it could lead to the loss of property and lives.
- It can ensure the safety of property and lives
- It can prevent insulation breakdown by keeping the system voltage under limits when a fault condition occurs
- It can provide an equipotential platform where electronic equipment can be operated
- Electrical noise in the cable can be reduced by providing an alternating path for induced current.
- It can minimize arcing faults
What is the difference between system earthing and equipment earthing
System earthing is done by considering the protection of electrical equipment, by stabilizing voltages with respect to ground. Whereas the equipment earthing is done for the protection of the personnel by maintaining the potential of non-current carrying equipment at or near earth potential. Mostly the system earthing is done by earthing the neutral of the supply system. In case of fault conditions the non-current carrying conductors of the electrical installations such as frames, enclosers, fencing could attain high potential with respect to ground so it would be dangerous to the person who comes in contact with it, to avoid this equipment earthing is done by connecting the non-current carrying conductors of the electrical system to the earth, it is done by the earthing system which consists of earth electrodes which conduct the fault current safely to ground.
Why coal and salt is added in earth pits
Coal is added to earth pits because it is a bad conductor, it is made up of burning wood. It has a property of absorbing water because it is porous. Salt is added to earth pits because it is basically sodium chloride and when it comes in contact with water it breaks into ions and helps in electrical conduction.
Terms related to earthing
Electrode in parallel
To get low and effective earth grid resistance earth electrodes are placed in parallel, minimum resistance can be achieved if the resistance area of each earth electrode is clear of another
Equipment bonding
It is an electrical connection which puts various exposed conductive parts at a substantially equal potential
Exposed conductive part
It is a part of electrical equipment which can be touched and it is not a live part until fault condition occurs
Extraneous conductive parts
It is a conductive part which can transmit a potential including earth potential and not the part of an electrical installation
Earth electrode
It is a metal plate or pipe or other conductors or an array of conductors which is electrically connected to the general mass of earth
Earthing or grounding resistor
It is a resistor by which the system is earthed and it will limit the current flow in the event of an earth fault
Types of earthing
T – it means direct connection to the earth, N – neutral, C – combined
S – Separate
When these are combined together it forms a type of system, the first letter shows how the supply source is earthed and the second one denotes how metalwork of installation is earthed and the third and fourth denotes the function of neutral and protective conductors
TT system
This system has a direct connection to the supply source to the earth and a direct connection of the installation metalwork to earth. An example of this is overhead power lines with earth electrodes and the mass of earth as a return path. TT system needs RCD protection
What are the advantages of a TT system
- Fault current is limited
- First fault tripping and human protection
- Risk of fire is removed
- Service continuity and simple design
- RCD’s are used
TN-S system
In this system it has a supply source that is directly connected to the earth, the neutral of the source is connected to the earth at one point only, which will be near to the source. The earthing terminal of the consumer will be connected to the metallic sheath of the distributed service cable.
TN-CS system
The TN-CS system is almost the same as the TN-S but the supply cable sheath is also the neutral, the supply neutral conductor of a distribution main connected with the earth at source and at intervals along its run. In this system, the distributor’s neutral conductor is also used to return the earth fault currents arising in the consumer’s installation safely to the source. To do this consumer’s earthing terminal will be linked to the incoming neutral conductor. It forms a combined neutral and earth conductor known as ‘protective earthed neutral’ and the earth and neutral are separate conductors and this system is known as protective multiple earthing.
What is an IT earthing arrangement
In this network, the distribution system has no connection to earth or it has only a high impedance connection. if a single insulation fault occurs it can cause the way for the flow of excessive currents through the personnel, because there is no low impedance circuit for the flow of fault current
