What is earthing?
In electrical terms, earthing, commonly known as grounding, refers to a system designed to protect electrical wires and components from damage caused by sudden electrical power surges. Its main purpose is to reduce the risk of dangerous electrical shocks from un-insulated metal parts of an appliance or electrical device. Earthing systems also prevent end users from electrical shocks in the event of a short circuit.
Purpose of Earthing:
(1) Safety for Human life/ Building/Equipment's:- To save human life from danger of electrical shock or death by blowing a fuse i.e. To provide an alternative path for the fault current to flow so that it will not endanger the user
- To protect buildings, machinery & appliances under fault conditions.
- To ensure that all exposed conductive parts do not reach a dangerous potential.
- To provide safe path to dissipate lightning and short circuit currents.
- To provide stable platform for operation of sensitive electronic equipments i.e. To maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the appliances or equipment .
Lightning, line surges or unintentional contact with higher voltage lines can cause dangerously high voltages to the electrical distribution system. Earthing provides an alternative path around the electrical system to minimize damages in the System.
(3) Voltage stabilization:
There are many sources of electricity. Every transformer can be considered a separate source. If there were not a common reference point for all these voltage sources it would be extremely difficult to calculate their relationships to each other. The earth is the most omnipresent conductive surface, and so it was adopted in the very beginnings of electrical distribution systems as a nearly universal standard for all electric systems.
Why earthing is required in an electrical installation?
Properly designed, constructed and installed electrical equipment and appliances should not have any of the non-current carrying conducting parts which is in contact with any current carrying part. But accidentally may be due to failure of insulation between current carrying and non-current carrying conducting parts of the equipment/appliance, if any of the non-current carrying conducting parts comes in contact with any of the current carrying parts of the equipment/appliance, there will be a static electrical charge developed in the non-current carrying conducting part. Now if any human being touches that non-current carrying conducting part of the equipment or appliance, the accumulated static charge will get a path to the earth through his body and hence it is discharged immediately, as a result he gets an electrical shock. But if the non-current carrying conducting parts that are metallic frameworks parts of the equipment or appliance properly earthed, then at the occurrence of touching between any current carrying part or live part to the non-current carrying part of the equipment/appliance, the live part of the equipment/appliance gets low impedance path to the earth through the properly earthed metallic frameworks and hence there will be a huge current drawn from source, passing to the earth through this path. As a result the circuit breaker or MCB, or fuses associated with this equipment/appliance will immediately break to discontinue the supply to the equipment/appliance. Thus proper earthing of non-current carrying metallic parts of electrical equipments and appliances provides safety of operation.
How to test the earth continuity path of an electrical installation?
In a properly designed wiring system, there are number of earth points located different positions throughout the wiring. For example each plug socket will have a third earthing point. The metallic body of each electrical appliance is connected to the earth through an earth points. This test ensures the continuity between an earth point and the actual earth. In this test, one terminal of earth continuity tester is connected to the earth point whose continuity is to be checked and other terminal of the tester is connected to the main earthing system of the building. The pointer of earth continuity tester will give the resistive value between the said earth point and actual earth. In any case, the value must not be greater than 1 ohm. If it is greater than 1 ohm, then the earthing connection should be physically rechecked and properly rectified to achieve desired minimum earth resistance.
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