Underground Cable Fault Detection: How a Fault Is Found

Updated: 28 October 2026

What is a cable fault?

A cable fault is any defect that stops an underground power cable carrying current safely, typically after insulation damage from an excavator strike, a defective joint, water ingress or prolonged overheating. Faults in underground cables fall into five groups: open circuit (broken conductor), short circuit (conductors touching), earth fault (leakage to screen or ground, low or high resistance), sheath fault and intermittent fault, which breaks down only under voltage. Each fault detection method suits some of these and not others.

How is an underground cable fault detected?

1. Isolate and test. The cable is switched out, earthed and tested with an insulation resistance tester to detect faults between cores or to earth.
2. Pre-locate. A time domain reflectometer (TDR) times a low-voltage pulse to estimate the fault distance along the cable length. High-resistance faults need arc reflection, surge pulse or voltage decay methods; Murray loop bridge tests remain an option when a healthy core exists.
3. Trace the route. The cable path is followed on the surface.
4. Pinpoint. A surge generator, or thumper, makes the fault flash over and a surface receiver picks up the acoustic and magnetic signal.
5. Excavate and repair. One small pit is opened over the spot, by hand near other services.

What does a cable fault locator do?

A cable fault locator, or fault locator, is a set of instruments: a TDR for distance, a surge generator, a pinpointing receiver and a route tracer, often combined in a DISCOM van. The underground cable fault locator price in India depends mainly on voltage class and surge energy; a full high-voltage system is a major investment, so many contractors hire a fault-locating crew instead.

Arduino-based underground cable fault detection projects

Many searches come from students doing project work. A typical project models a cable with resistors and an Arduino board: when a fault occurs, the output voltage changes and Ohm's law gives the location of the fault in kilometres; newer versions add AI-enhanced IoT alerts. Such models demonstrate the principle, but a live feeder still needs TDR, surge equipment and a traced route.

Why does the cable route matter so much?

Pre-location measures distance along the cable, not along the road. Cables bend around obstacles, carry slack loops at joints and rarely match old drawings, so a 300 m reading can land metres away from a tape on the footpath. An electromagnetic locator follows the signal, while ground penetrating radar adds joints, duct banks and the other services sharing the trench; see how GPR traces HT and LT cables. Before digging, confirm isolation and earthing, and treat every other cable as live.

How Mezux helps with cable faults

Mezux carries out cable fault locating as a separate order from route detection; tell us at the start if a feeder has failed so the right crew and equipment are sent. We map the route, joints and surrounding services with GPR and EM locating through our underground cable detection service. Route survey rates are on the GPR survey price list; fault work is quoted after a short call.

Sources

• IEEE 1234 – Guide for Fault-Locating Techniques on Shielded Power Cable Systems
• Mezux Touch field practice and published rate card (October 2026).