length of 4 core cable 95mm from substation LV VFD panel to
Motor at field approximately 150 meter. Motor stop and power
has been isolated from LV MCC ( Substation )to disconnect
Motor for services. After Motor completed service propose to
reinstall and reconnect Motor Cable, found earth cable
sparkling during touching at metal / motor body.
Inspect by clamp meter found earth cable have current flow
AC 1-2amps and all earth cable at MCC LV also have current
flow as same value. why it is happen?
Answer Posted / mrinmoyboruah
Cable insulation together with cable conductors form
capacitance. On nergising a cable this capacitance gets
charged and cable charging current flows even if no load is
connected at cable end. Similarly when cable is disconnected
from power source it retains the original charging energy
until it finds a conducting path to earth for discharge.
Hence before touching a disconnected cable all its
conductors including metal sheath and armours should be
connected to a earth path so that the stored energy in the
cable gets discharged.
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