When an underground cable fails, the first instinct is to start digging. That is usually the most expensive mistake you can make. A trench dug in the wrong place costs labour, road-cutting permission, restoration and, above all, more hours of shutdown. A good cable fault locator service should find the fault from the surface first and tell you exactly where to dig.
Before you hire anyone, ask these six questions. The answers will tell you whether they will find the fault in hours, or dig up half your plant looking for it.
1. “Will you test the cable before you start locating?”
A proper job starts with diagnosis, not equipment. The team should first disconnect the cable at both ends and run an insulation resistance (IR) test on each core, phase to phase and phase to earth. This tells them what kind of fault it is:
- Low-resistance fault: a core shorted to another core or to earth.
- High-resistance or flashing fault: insulation that holds at low voltage but breaks down under stress.
- Open circuit: a broken conductor.
Each type needs a different locating method. If someone arrives and starts walking the route with a detector without testing first, they are guessing.
2. “What equipment will you bring?”
Locating a fault is usually done in three stages, and each needs its own instrument:
- Pre-location with a time domain reflectometer (TDR) or an arc reflection set, which gives the approximate distance to the fault from the cable end.
- Pinpointing with a surge generator (often called a thumper) and an acoustic or electromagnetic receiver, which finds the exact spot on the ground.
- Route tracing with a cable route locator, which confirms where the cable actually runs. Old drawings are often wrong.
Ask which of these they own and will bring to site. A TDR alone gives you a distance, not a spot to dig. (We explain why skipping these stages costs days in why underground cable faults take days to find.)
3. “Do you work on HT cables as well as LT?”
Many plants have both LT feeders and 11 kV or 33 kV HT cables. HT cable fault locating needs higher-voltage surge equipment and engineers trained to work safely around it. If your fault is on an HT feeder, confirm the team has done HT jobs before, and ask what voltage their surge generator can deliver.
4. “How close will you mark the fault, and what if you are wrong?”
An experienced team should be able to pinpoint most faults to within a metre or so, which means a small pit, not a long trench. Ask how they confirm the spot before excavation, for example by listening for the flashover from two sides. Also ask what happens if the first pit is dry. A confident team will explain their process; a vague answer is a warning sign.
5. “Can you repair the cable after you find the fault?”
Finding the fault is half the job. The cable then needs a proper straight-through joint, made with the right jointing kit for the cable size and voltage, followed by testing before it is re-energised. If the same team can locate, joint and test, you avoid a second wait for a jointing crew and a second round of finger-pointing if the joint fails.
6. “What will I get in writing at the end?”
You should receive a short report that includes the IR values before and after repair, the fault type, its distance from a fixed reference point, the joint details and the final test results. Keep it. The next time that feeder gives trouble, this report saves hours.
A quick checklist before the team arrives
- Keep the faulty cable isolated and earthed, with a permit to work in place.
- Find whatever cable route drawings you have, even old ones.
- Note the cable size, type (XLPE or PILC), voltage and approximate length.
- Tell the team what happened when the cable failed: a trip, a smell, a sound, recent digging nearby.
- Arrange access to both ends of the cable.
Need a cable fault found today?
Tajalli Tech provides underground cable fault locating for LT and HT cables, including cable jointing and termination after the fault is found. We work across Uttar Pradesh, with teams for cable fault locating in Lucknow and cable fault locating in Kanpur. Call 0522-4956473 or send an enquiry with the cable details and we will tell you what we need to start.
Questions
How long does it take to locate an underground cable fault?
Most faults are located within a few hours once the team is on site, depending on the cable length, the type of fault and how accurate the route drawings are.
Can a cable fault be found without digging?
Yes. Pre-location and pinpointing are done from the surface. Digging is needed only at the marked spot to repair the cable.
What is a thumper in cable fault locating?
A thumper, or surge generator, sends high-voltage pulses down the faulty cable. At the fault the pulse flashes over and makes a sound that can be picked up on the surface to pinpoint the spot.
Should I replace the whole cable after a fault?
Not usually. If the IR test on the rest of the cable is healthy, a properly made straight-through joint at the fault is the normal repair. Repeated faults on an old cable are a sign it may need replacing.