Answer / mds.1490@gmail.com

n 3phase earthed system, phase to earth voltage is 1.732
times less than phase to phase

voltage. Therefore voltage stress on cable to armor is 1.732
times less than voltage stress

between conductor to conductor. Whereas in unearthed system,
(if system neutral is not

grounded) phase to ground voltage can be equal to phase to
phase voltage. In such case the

insulation level of conductor to armor should be equal to
insulation level of conductor to

conductor.




For example for a 6.6kV ungrounded system, 6.6kV/6.6kV (UE)
class cable has to be used while 6.6kV/3.8kV (E) class
cables are adequate for solidly earthed systems. The
UE-class cable is
naturally costlier than the earthed class of cable.

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