Earthing and it’s Importance

In low voltage three-phase system there are three single Phases measured between each phase and a common 

point called the “Neutral point”. In actual fact, the neutral is the common point of three Star-connected windings

where all three phases meet.

Meaning of Unearthed and Earthed System:

When there is an open circuit between the neutral point and earth, we say that theNeutral is Unearthed.

On the other hand if there is a connection between earth And neutral in this case system is called Earthed.

A directly earthed neutral strongly limits over voltages but it causes very high fault currents, whereas an

unearthed neutral limits fault currents to very low values But encourages the occurrence of high over 

voltages.

In any installation, service continuity in the event of an insulation fault is also Directly related to the earthing system. An unearthed neutral permits service Continuity during an insulation fault. Contrary to this, a directly earthed neutral, or Low impedance-earthed neutral, causes tripping as soon as the first insulation fault

Occurs.

However, in an unearthed or high impedance-earthed network, the damage is Reduced, but the equipment 

must have an insulation level compatible with the level of over voltages able to cope in this type of network. The choice of earthing system in both low voltage and medium voltage networks depends on the type of

installation as well as the type of network. It is also influenced by the type of loads  and service continuity required.

From above discussion it is clear that we have to choose a compromise between The two, supply continuity and insulation protection.