What is the purpose of earthing and why is it important

　　Earthing is the process of connecting the conductive parts of electrical equipment to earth. The importance of earthing is that it prevents over-voltage and over-current conditions, it provides a suitable path for fault currents and, if earthed, the fault currents will not damage the equipment. Earthing provides protection for personnel and equipment, and it prevents a rise in potential of equipment parts rather than live parts.

　　If a metallic part of electrical equipment comes into contact with a fire wire, the operator may be exposed to danger. This contact of the metal part with the fire wire may be due to a failure of installation or to a fault in the cable insulation. To avoid this, therefore, all equipment needs to be earthed.

　　Types of earthing

　　1. Earthing and phasing

　　2. Differences between earth and ground

　　How can we check that our earthing is correct?

　　We can do this in two ways, by using a lamp or by using a multimeter.

　　Checking the earth using a lamp

　　Before we start testing we must know the basics of phase, neutral and earth. If we look at the switchboard in our home we can see the three-pin socket and we must know which is the earth, phase and zero wires. The big pin of the three-prong plug is the earth wire, so to determine the phase and zero wires, take a tester and plug it into the three-prong socket, instead of connecting it to the earth slot, plug the tester into one of the other two smaller slots in the earth socket and if the tester glows, it is phase, if not, it is neutral. The phase is called the charged part because it supplies the current.

　　We can also check it by using a light, connecting one light wire to ground and the other to either of the two slots, so if the light glows then it is phase, if not then it is neutral. To make sure we have the correct earth to check this we have to connect the lamp to neutral and phase so that the lamp glows, connect the lamp to ground and phase and if it glows then if it glows with the same intensity as it glows in the phase and neutral connections then the earth is correct. So this means that the voltage is the same and the earth is correct.

　　Checking the earth using a multimeter

　　Set the multimeter to AC voltage and set it to high and connect it to the phase and neutral wires so we can get the voltage. So we get the value of the voltage between phase and neutral and then connect the multimeter between phase and earth and if the values are the same then we are correctly earthed. So this means that the resistance of earth is correct. The multimeter is then connected to ground and zero and if the voltage is below 2 volts then the earth is correctly earthed. If we get the voltage at both ends of the earth and the phase is different from the phase and neutral then it could be because of a grounding problem or it could be because the load is unbalanced.