In an earthed cable, the three phase of a cable are earthed 
to a ground.Each of the phase of system is grounded to 
earth.
Examples are 1.9/3.3 kv, 3.8/6.6 kv system
whereas, in an unearth system, the phases are not grounded 
to earth .As a result of which there are chances of getting 
shock by personnel who are operating it. Examples are:
6.6/6.6 kv, 3.3/3.3 kv system.