Hello everyone, in this article, I will discuss what is earthing, the necessity of earthing, and interview questions on earthing.
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Also read – Switchgear And Protection Questions And Answers.
What Is Earthing, Necessity Of Earthing
Meaning of Earthing
The method of connecting non-current carrying parts of the electrical equipment or accessories or neutral point of the supply system to the earth through the wire having negligible resistance is called electrical earthing.
Necessity of Earthing
- Earthing is used to protect human beings as well as provide safety to electrical appliances and appliances from leakage current.
- Earthing system is used to keep the voltage as constant (If a fault occurs on any one phase).
- To protect the Electric system and buildings from lighting.
- To serve as a return conductor in an electric transaction system and communication.
- Earthing system is used to avoid the chances of a fire in electrical installation systems.
- To provide the ground connections for the ground neutral system.
- To provide a means of positively discharged and de-energizing feeders or equipment before proceeding maintenance on them.
Points to be Earthed
According to Indian electricity rules and IEE (Institute of Electrical Engineers) regulations.
- Earth pin of 3-pin lighting plug sockets and 4-pin power plug should be efficiently and permanently earthed.
- The body of the generator, motors, and metallic parts of the transformer used for controlling energy should be earthed.
- According to the IEE in dc 3-wire system, the middle conductors should be earthed at the station of generating.
- According to the IEE stay wires of overhead lines should be connected to earth by connecting at least one strand to the earth system.
Question and Answers related to Earthing System
01. What is meant by the earth continuity conductor?
A. The conductor, by means of which the metal body of equipment or an appliance is connected to the earth, is known as earth continuity conductor (ECC).
02. What are maximum permissible values of resistance of earth system for (a) large power stations (b) major power stations (c) small substations (d) in all other cases?
A. Maximum permissible values of resistance of the earth system are as follows :
- Large power stations – 0.5 ohms
- Major power stations – 1.0 ohms
- Small substations – 2.0 ohms
- In all other cases – 5 ohms maximum.
03. What should be the minimum size of the earth continuity conductor?
A. The cross-section of earth continuity should not be either less than 2.9 mm square (14 SWG) or half of the installation conductor size.
04. What is the harm if earth resistance exceeds the permissible value of earth resistance?
A. The sensitivity of the protective equipment, system voltage, and the maximum fault current directly relate to the permissible value of earth resistance. In case the earth’s resistance exceeds the permissible value, then in the event of an earth fault, the fault current may not reach a sufficient value to operate the protective equipment (such as fuses or relays) and arises dangerous conditions.
05. What is an earth electrode?
A. The wire, rod, pipe, or metal plate used in the earth for the purpose of making a good electrical connection with the general mass of the earth is known as earth electrode.
06. What is earthing lead?
> A. The wire which connects overhead earth wire or any other apparatus to be earthed to the earth electrode is known as the earthing lead.
07. Why charcoal and salt is used in earthing?
A. Generally, alternate layers of charcoal and salt are used to increase the effective area of the earth and to reduce the earth’s resistance respectively.
08. What is the average resistance of the human body?
A. About 1000 ohms
09. What is current that is considered safe for a human body?
A. About 9 mA.
10. Give the applications of rod earthing?
A. Rod earthing is suitable for areas that are sandy in character.
I hope this may help you…..
Tags: What Is Earthing, Necessity And Interview Questions On Earthing
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