introduction.

In electrical supply systems, a grounding system defines the electrical potential of the conductors relative to that of the Earth's conductive surface. The choice of earthing system has implications for the safety and electromagnetic compatibility of the power supply. Note that regulations for earthing (grounding) systems vary considerably among different countries.

A protective earth (PE) connection ensures that all exposed conductive surfaces are at the same electrical potential as the surface of the Earth, to avoid the risk of electrical shock if a person touches a device in which an insulation fault has occurred. It ensures that in the case of an insulation fault (a "short circuit"), a very high current flows, which will trigger an over current protection device that disconnects the power supply.

The earth is made up of materials that are electrically conductive. A fault current will flow to ‘earth’ through the live conductor, provided it is earthed. This is to prevent a potentially live conductor from rising above he safe level.  All exposed metal parts of an electrical installation or electrical appliance must be earth. Generally the protective earth is also used as a functional earth, though this requires care in some situations.

The main objective of the earthing are:

a)   Providing protection against electrical shock.

b)  Provide an alternative path for the fault current to flow so that it will not endanger the user.

c)   Ensure that all exposed conductive parts do not reach a dangerous potential.

d)  Maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the appliances or equipment.

            The qualities of good earthing system are:

a)    Must be of low electrical resistance.

b)    Must be of good corrosion resistance.

c)    Must be able to dissipate high fault current repeatedly.

d)   Protection of buildings and installations against lightning.

e)   Safety of human and animal life by limiting touches and step voltages to safe values.

f)    Electromagnetic compatibility (EMC) i.e. limitation of electromagnetic disturbances.

g)  Correct operation of the electricity supply network and to ensure good power quality.

All these functions are provided by a single earthing system that has to be designed to fulfill all the requirements. Some elements of an earthing system may be provided to fulfill a specific purpose, but are nevertheless part of one single earthing system. Standards require all earthing measures within an installation to be bonded together, forming one system.