Cable fault location on ramp and stair heating throughout Austria and southern Germany

Key facts at a glance

For you as a business

A failed ramp heating becomes a problem with the first frost, and then immediately: the area must be gritted or closed as long as it does not heat. For property managers, facility service providers, developers, maintenance companies and electrical contractors the locating also decides whether a complaint turns into a dispute. The findings record where the damage sits and how it presents in the measurements – which counts when several trades have worked on the same build-up. From us come locating, marking and report; opening and repair are usually done by your own contractor.

How the job runs

1. Registration and details of the build-up. You describe which part of the area stays cold and ices over, since when, and whether only a section is affected. The laying record and construction photographs help, as do the assignment of the heating circuit distributor and the build-up above the cable – concrete, screed or paving bed.

2. Isolation and basic findings. Before the measurement the circuit is isolated and disconnected from the open-area controller and the distributor. As a rule your electrician does this; we can take it over if agreed beforehand. If several circuits lie under one area, it is first established which one has failed; only then is the fault classified – severed heating conductor, fault at the cold-lead connection, or short against the protective braid.

3. Heating up and narrowing down. The burn-down generator puts power onto the circuit until the conductor shows through at the top. The thermal imaging camera traces loops and turning points across the area, and where the pattern deviates, the spot sits. Only this turns the metre reading of the measurement into a point on the ramp.

4. Marking and handover. The fault position is marked on the surface and photographed, then you receive the report. Opening and repair are as a rule done by your contractor; on express request we also carry out the repair of heating cables and thin-bed heating mats ourselves.

Equipment and methods

Insulation and resistance measurement

At the start stands not the where but the what: the resistance of the heating conductor is held against the circuit’s nominal value, plus the insulation against the protective braid. A severed conductor leads to time domain reflectometry, a short against the braid to sheath fault location. On an area with several circuits this finding also decides which circuit is pursued at all.

Time domain reflectometry (TDR) on the heating conductor

A pulse is applied to the heating conductor and returns from the break. The travel time yields the length of the still intact piece, and this length, set against the total length laid, says in which loop the fault sits. For heating conductors no velocity factor is held in the instrument; calibration is done on an identical intact circuit, otherwise the metre reading can only be read relatively. Extensive ramps and long open-area circuits push the method to its range limit – one reason to determine the affected circuit cleanly first.

Sheath fault location

If the heating conductor shorts against the protective braid instead of being broken, its sheath is damaged. A pulsed direct current exits at the damaged spot, the voltage gradient is scanned on top of the surface, and exactly above the fault it reverses direction. Ramps, however, are usually heavily reinforced, and reinforcement smears this gradient – where it does not narrow down enough, the combination of heating up and thermal imaging takes over.

Burn-down generator for heating up

Under concrete, screed or paving bed the heating conductor cannot be seen – but it can be heated. The burn-down generator applies enough power for the conductor to stand out from the surrounding build-up and show through at the top. This makes two things visible: the laid route with loops and turning points, and, with energy applied deliberately, the fault as a locally deviating spot. Open areas need more patience for this than a thin bed in a bathroom: ramp build-ups are thick, and frost or wet on the surface draws heat away.

Thermography

The thermal imaging camera reads what the burn-down generator has put into the area: the heated conductor shows as a pattern, and where it breaks off or shows a tightly bounded overtemperature, the spot sits. Outdoors the image additionally depends on the state of the surface – a closed layer of snow or ice falsifies it, the section must be cleared for it. Wet ramps cool unevenly, which lengthens the recording time.

Costs and effort

There is no flat price: the size of the area, the number of heating circuits beneath it, the kind of fault and whether a laying plan exists determine the effort. We agree the cost range by telephone before the job. If the damage stems from a preceding trade, passing on the cost is a question of liability, not of measurement – the report provides the evidence for it.

Re-measurement happens within the job. If the opening shows that we measured wrongly, the re-measurement costs nothing. If the measurement held and the search at the marking was merely too imprecise or the opening too tight, we charge for the call-out – a measuring error by CFT is then not present. This is handled the same for every cable fault location, cable locating and pipe locating job.

Frequently asked questions