How to Locate Sheath Faults on MV Cables

Published 29 Jul 2020

Cable Repair Sheath

Image courtesy of EE Publishers

Republished with the Kind Permission of Sam Soady |

Eccentricity Pty Ltd Director /HV Operator / Cable Jointer


How to Locate Sheath Faults on MV Cables

Maintaining healthy sheath insulation is extremely important for the safe operation and lifespan of an MV cable. If there are faults in the outer sheath, you can expect an ingress of moisture, debris, and the premature degradation of the cables structure.

In turn, it is difficult to pinpoint the location of the fault as it can occur anywhere along the run of the cable (which is usually buried underground). There are, however, methods to accurately determine the location of the fault, which apply a surge energy of around 500J that tests for breakdown and insulation resistance of the outer sheath.

When Eccentricity comes across a sheath fault, we are able to utilise specific test equipment which enables us to locate the fault very easily and accurately.

Once the location of the fault has been determined, the cable can be exposed by means of vacuum digging which prevents further damage. It is at this point you can physically see the damage to the outer sheath of the cable. Damage usually occurs due to poor cable laying methods or not enough care taken during installation.

Rectifying the damage can sometimes be as simple as installing some resin filled zip tube heat shrink, which re-seals the outer sheath and re-establishes the insulation resistance. In some circumstances, further damage to the under layers of the MV cable can occur and extra repairs such as rectifying termite protection or other protective layers within the cable must be completed.

Once the integrity of the cable has been re-established from the repairs, it is important to re-test the cable prior to backfill to prove the rectification works. Once verified, the cable can be backfilled and tested once again in its final resting position.

About Eccentricity

Eccentricity logo

Eccentricity is a specialised Brisbane based company with a team of dual trade electricians and cable jointers. Our technicians are fully qualified to work on cables up to 66kV, including XLPE, PILC and EPR cables, backed by over a decade of industry experience.

With a modern and fully compliant fleet of industry vehicles, we are capable of accessing any high risk environment to perform works with a wide range of major MV HV cable jointing projects including, mining, oil, gas, renewable energy, and high voltage transmission networks.

Eccentricity has the capacity for small or large scale projects, providing reliability of power networks wherein client satisfaction is a top priority. We provide a high level of quality with all aspects of both installation and commissioning, ensuring we comply with all relevant regulations and legislative provisions.


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Thorne & Derrick International are specialist distributors of LV, MV & HV Cable Installation, Jointing, Duct Sealing, Substation & Electrical Equipment – servicing UK and global businesses involved in cable installations, cable jointing, substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV.

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