Earthing or Grounding refers to connecting metal parts of electrical equipment to an earth electrode.
It must be connected back to the source of supply by an earth or ground conductor so that if the metal becomes live during a fault there will be a large fault in the phase conductor feeding that fault and the fuse or circuit breaker or other overcurrent protection device on that phase conductor will cut-off the supply to the fault.
Grounding means connecting a wire or other conducor to the earth. This is done by connecting the wire, or equipment to be grounded, to a copper rod that has driven into the ground. The earth is an adequate conductor and current will flow through it.
When short circuits occur or when a device is connected from an energized wire to ground, the grounding wire provides a means of completing the path for the current. This completed path will allow excess current to flow which will blow one of the fuses, thus removing the current and-the danger. The grounded wire of the system must never be fused, for if this fuse should blow, the entire system would no longer be grounded, and considerable danger could be present. During the few seconds, until the fuse blows to interrupt the fault current, the equipment casing, or other equipment where the fault is, may have a significant voltage. Earth bonding to the building structure and other parts means that these elements will have a similar fault voltage reducing the magnitude of any electrical shock due to this voltage.
Distribution systems should be grounded to a grounding electrode every 300 feet to maintain an adequate ground. generating equipment, like all other equipment, must also be grounded.