The function of the earthing system is two-fold.
To provide a low enough impedance path, via the earth conductors, back to the supply source so that in the event of a failure to earth of a live conductor, sufficient current will flow safely along a predetermined route to enable the circuit protective device to operate.
To limit the potential rise on all metalwork to which persons and animals normally have access, to a safe value under normal and abnormal circuit conditions. The bonding together of all normally exposed metalwork, such as gas, water, central-heating pipe work etc., and the connection of that bond to the earth terminal, will prevent the possibility of a dangerous potential difference arising between adjoining pipe work under both normal and abnormal conditions.
The main objectives of earthing are as follows -
- To ensure safety of life and property from hazards of electric shock and electric fires.
- To ensure that system voltages on healthy lines remain within reasonable limits under fault Conditions thereby preventing insulation breakdowns.
- To provide a low impedance path to facilitate the satisfactory operation of protective devices under fault conditions.
- To minimize arcing burn downs as in an earthed system arcing fault would produce a current in ground path thereby providing an easy means of detecting and tripping against phase to earth arcing fault breakdowns.
- To provide an equipotential platform on which electronic equipments can operate.
- To provide an alternative path for induced current and minimize the electrical noise in cables.
