what is the difference between earthed and unearthed cable?

Answer Posted / ravi kaslikar

Power Cables can be classified into Earthed and Unearthed
cables. The terms "earthed" and "unearthed" refer to the
application for the which the cables are to be used.

By Earthed system, we mean a three phase system whose star
point is grounded directly. In this case, in the event of
the earth fault, the voltage in the faulty phase will
become zero. The voltage between the healthy phases and the
ground will be the same, 11kV/1.732 or 6.6/1.732.

However, in case of an earth fault in an ungrounded system,
the voltage between the healthy phases and the ground will
be equal to the phase to phase voltage. i.e. 11kV or 6.6 kV.

Hence, the insulation level of these cables needs to be
higher.

Thus a cable suitable for a 11kV earthed system will be
suitable for a 6.6kV unearthd system.

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