Why is fault finding so important for reliable cabling connections?
It’s inevitable that cable faults will always occur at the wrong time – whether you’re halfway through a manufacturing batch or busy in the office – and any interruption to your power supply is not only a real pain point, but can also be very costly.
That’s why locating the fault as quickly as possible, effecting a repair and restoring your supply is so important.
What is a cable fault?
Cable faults can arise for a multitude of reasons, including mechanical damage, water ingress, poor jointing practice or materials, partial discharge and deterioration due to age. Faults can occur on all types of cable, at any age or voltage.
The most common issues are short circuit faults – which can be phase to phase or phase to earth – and open circuit faults, where a break in the cable arises. Sometimes, a combination of the two can take place. In many instances, the fault can start as a minor point of damage to the cable or joint, where a slow but gradual ingress of water occurs, until the insulation resistance breaks down to a point where flashover happens. This results in the protective device kicking in and cutting off the mains supply to the circuit.
In some cases, a fault will ‘clear’ after the protection has operated – these are called transient faults. This can be very disruptive, detecting such intermittent faults can prove difficult and means problems are likely to reoccur at some point down the line. Typically, this type of fault will eventually result in a permanent issue.
Another category is a sheath fault, which is where a break in the outer casing of the cable has occurred and can lead to a potential fault through water ingress. If found early enough, such an issue can be repaired, preventing possible cable failure in the future.
How are faults located?
Following a call out, our engineers review any protection that has operated and – once an insulation resistance test has been conducted – may attempt to re-energise the whole or part of the system, to restore mains supply where possible.
The engineers will walk the cable route and visually inspect the cable, joints and terminations that can be seen for any signs of failure, whilst also looking for obvious signs of potential cable damage locations – such as recent excavations or new structures.
Initial tests are then be carried out to determine the characteristics of the fault. At this point – and depending on the observations from this primary review – our engineers use various apparatus to locate the fault. This involves firstly pre-locating the fault position, followed by using pinpointing techniques in the identified area to more precisely locate the fault, prior to excavation and further visual inspections.
Once found, our team conducts the necessary repairs using spare cables, joints and terminations they carry with them – retrieving different types and sizes from our vast warehouse stock if needed. When the mend is complete, our engineers perform insulation resistance and continuity assessments prior to re-energising the circuit. We also offer VLF (very low frequency) testing if requested before restoring the supply.
Our sheath fault finding and repair service is beneficial for both newly or previously installed cables, as it can help identify potential issues early and prevent cabling problems further down the line.
What tools are involved?
Engineering expertise is vital to the cable fault location process, but innovative technology has a large part to play too. That’s why over recent years we have invested a further £65,000 into additional fault finding equipment, enabling us to efficiently locate, diagnose and resolve these cabling issues.
The Megger SMART THUMP ST16 Portable Cable Fault Location System is a safe, efficient and user-friendly piece of equipment that our engineers can utilise to quickly identify, pre-locate and pinpoint an array of different cable problems – on new or old systems and primarily for use on cable voltages up to 35kV. Circuit lengths of 3 miles long can be tested using this equipment, which makes it invaluable for the large-scale connections we are often contracted to work on. Employing high voltage surge wave technology combined with TDR arc reflection, this equipment has a receiver that utilises acoustic and electromagnetic fault pinpointing to locate the fault within inches.
When used under the right conditions, Portable TDRs (Time Domain Reflectometers) can identify the location of both open and short circuit faults very accurately. We also use High Resistance Fault Locators, which incorporate bridge technology – this is a tried and tested method that has been used for many years. But whilst it may be classed as an ‘old technique’, it is still relevant today when pre-locating difficult-to-find high resistance faults.
With a test voltage up to 10kV, the MFM10 Sheath Fault Locator is additionally used to find sheath faults easily and quickly through bipolar measurement. Plus, Vivax-Metrotech vLoc Series 2 cable location equipment enables quick and accurate cable tracing, depth measurements and GPS logging to be conducted using the latest technology.
Why is a speedy response so important?
When it comes to tackling cabling faults, many instances are urgent call-outs where supply has been disrupted – often in industrial or manufacturing plants – which means that after safety, the main priority is getting systems back up and running. Having state-of-the-art equipment at our immediate disposal is a great advantage and reassurance for our clients, who know they can rely on our responsive and efficient services – 24 hours a day, 365 days a year.
We’ve been finding cabling faults and conducting VLF and sheath testing for many years. With extensive experience in installing and maintaining cable systems, our highly-qualified jointers and fitters are well-trained in using this specialist equipment, using it to locate and repair cable faults on a regular basis – often under significant time pressures.
To find out more about our cable fault finding, VLF and Sheath testing services, please get in touch!