M
AVTMST16 Rev 1 May 2016
34
How to Pinpoint a Sheath Fault OR a Ground Fault in an
Unshielded Low Voltage Cable (both must be directly
buried)
Following a failed sheath test (see page Error! Bookmark not defined.) fault
location of the sheath fault in
direct buried cables
based on the step voltage
method (earth gradient method) can be performed with the SMART THUMP
serving as HV pulse generator (limited to a voltage of 5 kV, see below) An
additional receiver is required to read the strength and polarity of the earth
gradient voltage (e.g. Megger ESG-NT) in order to pinpoint the sheath fault.
When approaching the fault position, the step voltage increases quickly and
decreases to a zero reading directly over the fault and then will swing to a strong
voltage of the opposite polarity.
Proceed as follows to pinpoint the sheath fault:
Step Description
1
Select the menu item from the submenu.
2
Confirm the following two notices with .
3
Adjust the surge voltage and select to confirm the value.
4
Press the green illuminated “HV ON” button .
5
Select to start the sheath fault pinpointing mode. The Voltage Selection, Automatic
should be disabled (see page 18) allowing you to select a voltage between 2 and 10 kV.
If the Voltage Selection , Automatic is enabled, the maximum voltage is limited to 4 kV,
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