In the power system, grounding or earthing means connecting the frame of electrical equipment (non-current carrying part) or some electrical part of the system (e.g. neutral point in a star-connected system, one conductor of the secondary of a transformer, etc.) to earth i.e. soil.
This connection to earth may be through a conductor or some other circuit element (e.g. a resistor, a circuit breaker, etc.) depending upon the situation.
Advantages of Earthing
Grounding or earthing offers two principal advantages.
First, it provides protection to the power system.
For example, if the neutral point of a star-connected system is grounded through a circuit breaker and phase to earth fault occurs on any one line, a large fault current will flow through the circuit breaker. The circuit breaker will open to isolate the faulty line. This protects the power system from the harmful effects of the fault.
Secondly, earthing of electrical equipment (e.g. domestic appliances, hand-held tools, industrial motors, etc.) ensures the safety of the persons handling the equipment.
For example, if insulation fails, there will be a direct contact of the live conductor with the metallic part (i.e.frame) of the equipment.