Grounding is a safety measure for electrical and electronic systems whereby the user is protected from accidentally coming in contact with electrical hazards. For instance, refrigerators at home usually stand on rubber feet, even when operating from the AC outlet. Although electricity enters the refrigerator and runs through most of the electrical components within it, it has no connection to the outer metal body. Rather, the outer metal body of the refrigerator connects independently to a green grounding wire, which leads to the third pin (the thickest one) on the power plug.
If the outer metal body of the refrigerator was not grounded as above, and for some reason, electricity came in contact with the outer metal chassis such as from leakage, it would cause injury to anyone, if the person were to touch the refrigerator. Connecting the outer metal body to the grounding wire protects the person from being electrocuted, as electricity present on the metal body passes to the earth directly instead of through the person.
This is presuming the third pin on the power plug is connected to a good grounding arrangement outside the building. Typically, this arrangement is a ground rod, or a grounding electrode inserted into the soil. The arrangement works because the earth is a good conductor of electricity, and the overhead transformer that supplies power to the area, also has a grounding arrangement near it, which completes the circuit for the leakage current of the refrigerator. Therefore, a good grounding arrangement is essential for safety.
Apart from safety, most of the electronic equipment, such as computers, microwave ovens, LED lights, televisions, and more, need to be securely grounded to operate effectively. This is because most electronic equipment generate huge amounts of electrical noise that affect other equipment nearby. This can cause damage to an equipment, or cause it to work less effectively. Proper grounding helps to remove the unwanted noise, allowing all equipment to inter-operate more effectively.
Another advantage of a good grounding system is it helps protect against lightning. Lightning has high-voltage electricity with fast rise-times and causes large magnitude currents. A grounding system must present a low-resistance path for the high currents from a lightning strike to enter the earth, without causing damage to the building or equipment within.
Therefore, low resistance or low impedance of grounding is the key to protection from leakage of electricity, electrical noise, and lightning strikes. A good practice is to have all grounding connections as short and direct as possible, and connected with a heavy gauge wire, preferably made of copper. This ensures minimization of inductance and reduces the peak voltages induced.
The effectiveness of the grounding system in coupling the unwanted electricity to ground depends on a number of factors. This primarily includes the geometry of the ground electrode, the size of the conductors, the effective coupling into the soil, and the resistivity of the soil around the electrode.
Therefore, the basic requirements of any ground installation are to maximize the surface area of the electrode with the surrounding soil. This helps to lower the earth resistance and impedance.