SOS Electricals | How to Locate Underground Cable Faults
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How to Locate Underground Cable Faults

underground cables

30 Oct How to Locate Underground Cable Faults

Instances of underground cable faults are inevitable. Once in a while, power transmission as well as distribution will be hindered by a fault that may not be obvious to the naked eye. Although there are new detection technologies that an electrician can rely on, at the end of the day, he or she will have to rely on their own skills and experience to pinpoint where the fault is. Each scenario calls for a particular method of detection; the fact that these cables are often buried underground only makes the task more difficult. Luckily, there a few reliable methods that one can use in underground cable fault detection;

Underground cables




  1. Sectionalizing; sectionalizing is the oldest, easiest ways to detect where the fault is within an underground cable. Like the name suggests, it entails cutting and physically splicing up the cable. Usually, the cable is cut into smaller sections and each piece is tested via an ohmmeter or a tester. By testing each of the cable pieces, you’re able to narrow down on the exact part that requires repair. The only major disadvantage with this method of cable fault detection is that it is laborious and means digging out the underground cable repeatedly.
  2. Thumping; this is not a very effective method, but it is worth giving a try anyway. A high voltage is supplied through the faulty cable, and the electrician listens for any noise above ground. For you to clearly hear the noise made by the current flow, the voltage has to be really high, sometimes up to 25kV. This may damage the cable’s insulation and should thus be done in moderation. If successful, this detection method saves you from the laborious task of splicing the cable.
  3. TDR; Time Domain Reflectometry is one of the latest technologies used to locate a faulty underground cable. It works by sending low energy signals via the faulty cable. In theory, a perfectly functioning cable sends back that signal within a known duration and manner. The TDR screen helps the electrician utilize the given data to estimate where a cut or splice may have occurred within the cable. This is the only major disadvantage of TDR; for all its technological advancement, it doesn’t pinpoint the exact lotion of a fault. Besides, it is not helpful if you’re dealing with faults that have resistance exceeding 200 ohms. This means that locating minor faults that haven’t qualified to outright power shorts is a tall task for TDR.

Like in all electrical matters, locating an underground cable fault should only be done by a qualified electrician or engineer. He or she should always have the right tools for the job, and due diligence employed at each stage of the task. Usually, the main power should be off when the fault tests are being conducted, unless otherwise. It is also always better to rectify underground cable faults when the ground is dry, compared to when it is wet or it has rained heavily.