Earthing vs Grounding
Earthing and Grounding are basically same in concept. Difference between Earthing and Grounding is one of the most confused and misunderstood concepts. The importance of grounding in commercial and industrial installations can never be underestimated. Circuits of machines are grounded to provide an effective return path from the machines to the power source. There are many benefits of grounding to owners of buildings. These include maximum equipment protection, reducing shock hazard, and cost savings which accrue by avoiding machine servicing. Confusion arises with interchangeable terms such as earthing, grounding and bonding are used in these contexts.
Earthing is said to have been accomplished through bonding of a metallic system to earth. It is normally achieved by inserting ground rods or other electrodes deep inside earth. The purpose of earthing is to minimize risk of receiving an electric shock if touching metal parts when a fault is present.
In daily life, you can see a good example of grounding if you go near an electricity pole. What you will notice is a bare wire coming down from the top of the pole and going inside the earth. This coil is buried deep inside the ground (to a depth of 2-3 meters). All wires running between poles are connected to this grounded wire. In a similar manner, close to the electric meter of your house, there is a 2 meter long copper rod driven into the ground. All the neutral plugs in your house are connected to this metal rod.
So we see that grounding and earthing are basically same things. These are actually different terms for the same concept. Earthing is more commonly used in Britain and most of the commonwealth countries, while Grounding is the word used in North American countries.
Over voltage protection
Because of lightening, line surges or unintentional contact with other high voltage lines, dangerously high voltages can develop in the electrical distribution system wires. Grounding provides a safe, alternate path around the electrical system of your house thus minimizing damage from such occurrences.
Thus we can see that safety is the main reason why grounding or earthing is resorted to.