3 Types of Underground Cable Faults and how to use Megger for identifying them

Undergrounds Cables are generally laid directly in the ground and compared to power transmission and distribution lines the chance of occurrence of fault on underground cables is less. However, once a fault occurs on underground cables, it is difficult to locate and repair the fault because cables are not visible.

Given below are 3 Types of Underground Cable Faults.


Earth fault

When conductor of a cable comes in contact with earth, it is known as earth fault or ground fault. In order to find this fault, one terminal of the megger is connected to the conductor while the other terminal is connected to earth. A reading of zero on megger implies that conductor is earthed.

The same procedure is repeated for the other conductors of cables as well.

Short-circuit fault

A short circuit fault occurs whenever two conductors of a multi-core cable comes in contact with each other due to insulation failure. Just like earth fault, the short-circuit fault can be identified using a megger.

In order to find short-circuit fault using megger connected two terminals of the megger to any two conductors. A zero reading implies short-circuit fault between these conductors. The same step is repeated for other conductors taking two at a time.

Open-circuit fault

The open circuit fault occurs whenever there is a break in the conductor of a cable. Just like earth and short circuit fault the open-circuit fault can be checked using a megger. In order to achieve this, the three conductors of the 3-core cable at the far end are shorted and earthed.

After this, the megger is used to measure the resistance between each conductor.

The megger will indicate zero resistance in the circuit conductor that is not broken.

In case the conductor is broken, the megger will indicate infinite resistance in its circuit.

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