A good earthing allows the faulty current to pass to the ground easily through conductors. Before charged electricity to an installation or a machine earth connection must be present there. Number of earth connections will be depending on the connected phase (i.e. one earth connection for single phase and two earth connections for three phase supply).
Table of Contents
What is the Earthing
The conductive mass of the earth whose electrical potential is taken as zero. Earthing is a connection between an earth electrode and current carrying metal parts and an electrical system. A good earthing gives very low earth resistance to flow leakage current from a circuit to earth.
Type of Earthing
Generally, earthing has two types one is system earthing and another is equipment earthing.
System earthing is the connection between the neutral point of a transformer, generator, rotating machine etc and earth.
Equipment earthing is the connection between non-current carrying metal parts and earth.
What will be the effect if earthing resistance is very high?
If the earthing resistance becomes very high, then the leakage current will flow very slowly through the conductors as a result different kinds of fault may occur. It will injure human beings also if they touch anybody noncurrent carrying metal parts of electrical equipment.
Type of earth electrodes
Four types of earth electrode generally used-
What is an earthing resistance tester or earth tester?
Earthing resistance tester or earth tester is used to measure resistance or impedance of earth.
Type of earth tester
Digital and analogue both types of earthing resistance tester or earth tester are available. According to the value of resistance, different kinds of earth testers are used.
How to measure earthing resistance by earth tester
An earth testing meggger has three terminals E, P & C but some megger has four terminals P1, P2 & C1, C2, in this megger P1 & C1 to be short and it will be “E“terminal.
For testing earth resistance, E terminal to be connect with earth electrode (which resistance we will check) then P or P2 terminal is connected with the potential spike electrode grounded at a distance of about 20 meters away from the instrument or earth electrode and C or C2 terminal is connected with a current spike electrode grounded at a distance of about 40 meters away from the instrument of earth electrode in the same line with the other electrode. By rotating the handle of the analogue megger and pushing the test button of the digital megger, earthing resistance can be shown reading the value. Exact value of earthing resistance will come after deducting the P & C wires resistance (P & C terminal wires will be connected with E terminal and rotate the handle can be shown the resistance value).