Cable faults
Cable fault location on street lighting networks in Austria and southern Germany
A cable fault in a lighting network rarely puts a single luminaire out of action; it takes out a whole section. Between the feeder pillar and the last lighting column there are many hundreds of metres of cable, of different ages and materials, often without a reliable as-built plan. CFT narrows the fault down column by column, locates it and marks it in the street, so that the maintenance contractor excavates at one point instead of along the pavement. Report the dark section on +43 (0) 2252 53169, from Germany on +49 (0) 173 6842932, or in writing to office@cft.at, and we will clarify network records, access and an appointment.
What we do on site
The condition is measured first – insulation and resistance say which core is affected and how high-resistance the fault is. The isolated ring is then separated at the columns until the fault lies between two of them; who opens the columns is settled beforehand. Only on that short stretch do we measure finely, because length-dependent methods presuppose a known layout. You receive the damage report as a PDF, in which the section is recorded with reference to the columns – usable after the repair as well.
Key facts at a glance
| Methods | Insulation and resistance measurement, twist method, Ley effect, bridge measurement (Murray loop), time domain reflectometry (TDR), electromagnetic cable locating, cable identification in trench and cable tray |
|---|---|
| Application range | Lighting networks of local authorities, municipal utilities, maintenance companies and electricians; fault location on aluminium, lead and copper cables of all kinds |
| Duration | Not under two hours; anything beyond that is charged by the hour. Two hours are usually enough for one or two fault locations. |
| Result format | Damage report as a PDF |
| Service area | The whole of Austria, from the head office in Traiskirchen; southern Germany, that is Bavaria and Baden-Württemberg, via CFT Group Deutschland GmbH, Lange Zeile 27, D-85435 Erding |
For you as a private customer
The street lighting outside your house belongs to the municipality or to the network operator; you therefore report a dark luminaire to them, and location work is instructed through the local authority. The position is different with lighting on your own land, that is yard, path or driveway lighting: we treat these cables like any other buried supply cable, as described under service and supply cables.
For you as a business
For local authorities, municipal utilities, maintenance companies and electrical contractors, precise location saves excavation: fewer road openings, shorter closures, lower costs. Lighting networks are rarely homogeneous – over the decades aluminium, lead and copper cables come to lie in the same ring, and branch joints are not documented. We work section by section and record what we learn about the actual route; alongside the finding, this produces a piece of as-built documentation. We travel beyond our own region for this service, throughout Austria and in southern Germany: the measuring equipment and the evaluation for lighting rings that have grown over time are not available everywhere, and the road opening that is saved justifies the journey.
How the job runs
1. Coordination and network records. You report the affected section, the feeder pillar and, if available, the plan with column numbers. Access to the feeder pillar and to the column bases is clarified in advance.
2. Isolation and current state. The section is isolated and de-energised and disconnected at both ends – normally by your own electrician, by us if you wish and if that is agreed in advance. Insulation and resistance are then recorded: which core is affected, how high-resistance the fault is, and whether it is an open circuit, an earth fault or a core-to-core fault. We also note from which column onwards the section stays dead.
3. Narrowing down section by section. The ring is disconnected at the columns until the fault is enclosed between two columns. Only on this short length is detailed work carried out.
4. Pinpointing and report. The fault position is determined, marked in the street and photographed. You receive the report with the section, the column reference and the route drawing; the repair is carried out by your maintenance contractor, CFT does not carry out repairs.
Equipment and methods
Insulation and resistance measurement
Before any narrowing down comes the question of what one is dealing with. On the isolated section insulation and resistance are recorded core by core; from this follow the type of fault and how high-resistance it is. In a ring that has grown over time this finding has a second use: it shows whether only one position has failed or whether the cable returns poor values over its whole length – in which case fault location is only the beginning and the real question is the age of the cable.
Twist method
Multi-core cables are twisted, with the cores running in a helix around the axis of the cable. If a locating signal is fed in such a way that it travels out and back along these cores, a rise and fall in the rhythm of the twist appears at the surface, and it breaks off at the fault position. The method requires a low-resistance fault between two cores of the same cable; with an earth fault or a plain open circuit the pattern does not appear, and there we work with bridge measurement or time domain reflectometry.
Ley effect
The Ley effect narrows down faults on multi-core buried cables when there is no clean reflection pattern: what is evaluated is the change in the locating signal along the route, which behaves characteristically as far as the fault position and no longer does so beyond it. It narrows the position down; it is not pinpointing.
Bridge measurement (Murray loop) in the lighting network
Bridge measurement works with resistances, and in a ring that has grown over time this is where it is sensitive: aluminium and copper follow one another in the same run, and an unknown change of material shifts the result without this being apparent from the measurement. It is therefore only carried out after the section-by-section narrowing down, once the material and construction of the short length are known.
Time domain reflectometry (TDR) and its limitation in the ring
Time domain reflectometry gives a distance most quickly when there is a clear open circuit. Its limitation shows with a large number of branches: every outgoing connection at a column and every cable joint produces a reflection of its own and the trace becomes ambiguous – which is why it is only applied after the ring has been disconnected.
Electromagnetic cable locating and cable identification
Cables do not always follow the edge of the pavement shown on the plan, so the actual route between the columns is recorded with the locating signal. At the base of the column the incoming and outgoing cables come together, often with third-party services alongside them; cable identification establishes, before anything is disconnected, which run leads to the next column.
What you receive
You receive the fault position marked in the street and a damage report as a PDF with the section, column reference, method, readings and photographs. Added to this is the route drawing of the recorded route between the columns, which remains useful after the repair as well.
Costs and effort
There is no flat rate. The effort involved depends on the length of the ring, the number of columns, the cable material and the accessibility of the feeder pillars. We agree the cost range with you by telephone before the job. Insurance cover is not the normal case in a municipal lighting network, and where a third party has caused the damage the question of liability has to be clarified separately.
The re-survey is part of the scope of services. If the fault is not at the position we marked because our measurement was wrong, we return free of charge. If the measurement was correct and the road opening was simply not set out precisely enough or not taken deep enough, we charge for the call-out, because in that case there is no measurement error on CFT’s part. Which of the two applies is shown by the re-survey on site at the open excavation.
Frequently asked questions
Can measurements be taken while the lighting is in operation?
Measurements are taken on an isolated and de-energised cable, not in operation. Your own observation is helpful: whether the section fails immediately, whether the protective device trips later, or whether the failure only occurs in wet conditions.
We have aluminium, lead and copper cables in the same ring. Is that a problem?
No, that is the normal case in networks that have grown over time. What matters is working section by section, because length-dependent methods require a known cable construction.
Do the column bases have to be opened?
As a rule, yes, because disconnecting at the columns is the quickest way to enclose the fault. We clarify in advance who opens the columns.
We have no as-built plan. Is it still possible?
Yes. The route between the columns is recorded with electromagnetic cable locating and transferred into a route drawing, which forms part of the report.
The road opening is open and the cable is undamaged. Who pays for the re-survey?
That depends on what caused it. If our measurement was wrong, we re-survey free of charge. If our measurement was correct and the road opening was simply not set out precisely enough or not taken deep enough, we charge for the call-out, because in that case there is no measurement error on CFT’s part. The re-survey itself is part of the service in both cases.
Is it enough to repair the position that was found?
In a ring that has grown over time, rarely. The cable is cut for the joint, and both sides have to be measured afterwards: a ring whose cable has failed in one place frequently has further weak points, particularly at the transitions between materials. Your maintenance contractor can carry out this check, or we can – without it, the next dark section is only a matter of time.
Contact and opening hours
For jobs in Austria: CFT Group GmbH, Wiener Straße 99, A-2514 Traiskirchen, +43 (0) 2252 53169. For southern Germany: CFT Group Deutschland GmbH, Lange Zeile 27, D-85435 Erding, +49 (0) 173 6842932. Monday to Thursday 8:00–16:30, Friday 8:00–12:00. Outside office hours, write to office@cft.at and we will come back to you on the next working day.
Related services
Medium voltage (MV)
For the supply level ahead of the lighting feeder pillar.
Control and coaxial cables
For switching and control cables of the lighting circuits.
Network locating and cable identification
When the entire route is to be documented.
Site and route utility clearance surveys
Before opening up the road.
Describe the findings.
The more precisely you describe the findings, the more directly we can go to work. Plans, readings and photos help us settle the method in advance.
What happens next
- We read your message and match the case to a method.
- We come back to you – usually with a question that shortens the appointment.
- We confirm the appointment and what it costs before anyone sets off.
Rather talk?
+43 (0) 2252 53169
Mon–Thu 8:00–16:30 · Fri 8:00–12:00
Describe your case.
Fastest by telephone – then we settle straight away which method fits and what you should prepare.
Outside office hours, write to office@cft.at.