FLEXA protective conduit for rail vehicles - how to choose a system and what factors should you consider when making your choice?
All these factors have a direct impact on the safe transmission of power and data and, consequently, on the continuity of vehicle operation. For this reason, selecting cable protection systems cannot be based solely on the price of individual components. The total cost of ownership (TCO) of the vehicle is becoming increasingly important, covering not only the initial purchase but also installation, approval, servicing, repairs, and the cost of potential downtime.
Apparent savings at the purchasing stage may encourage so-called system hybridisation, meaning the combination of protective conduits, connectors, and supports from different suppliers. In practice, however, such an approach increases the risk of component mismatch. Differences in corrugation profiles, the formation of micro-gaps under vibration, or the loss of the declared IP68 or IP69K protection rating may eventually lead to installation damage and premature failures.
In the railway industry, the consequences of such failures are particularly severe. The costs of diagnostics, repairs, component replacement, and taking a vehicle out of service may be many times higher than the initial difference in component prices. For this reason, fully integrated cable protection systems, in which all components are designed and tested as a complete solution, are being used increasingly often.
Using a complete solution from a single manufacturer provides:
- full material and design compatibility
- faster and more predictable installation on the production line
- a simplified testing and approval process
- retention of the declared technical parameters of the entire system
- lower servicing costs throughout the vehicle’s operating life
In the following sections, we present a guide to selecting FLEXA cable protection systems for five key structural zones of a railway vehicle. Each zone has different requirements, so the correct selection of conduits, connectors, and fastening elements should be based on the conditions prevailing at the specific installation location.
1. Inter-car connections - the zone of extreme dynamic loads
The transition area between rail cars is the direct interface connecting two independently moving vehicles. It is responsible for integrating the main power supply systems, sensors, and control buses. This zone is exposed to the highest level of dynamic loads in the entire trainset.
Risk analysis and selection criteria
Most standard plastics deteriorate rapidly in this area due to continuous multi-axis bending, torsion, and tensile forces occurring when the train negotiates curves or switches. Additional risk factors include vibration, impacts, abrasion of the protective conduits against coupling components, and the need to operate in extreme ambient temperatures.
System solutions
Material selection (PA 12 plastic): Highly flexible ROHRflex PA 12+ and PA 12F+ protective conduits are consistently recommended for this zone. Polyamide 12 has a unique molecular structure that provides exceptional fatigue resistance under continuous reverse bending. Crucially, PA 12 has extremely low hygroscopicity, which means that its mechanical properties remain unaffected by weather conditions. The material does not whiten and retains exceptional low-temperature impact resistance in severe frost, down to -50°C, eliminating the risk of cracking. In addition, ROHRflex PA12+ is a three-layer conduit, which further increases its flexibility and freedom of movement.
Movement-compensating connectors: To eliminate stress concentration and the notch effect at conduit ends, specialised straight and angled connectors with optimised entry geometry should be selected, such as RQGK, RQGKZA, RQBK90, RQBK45DR, RQBK90DR, and RQGKST. The RQBK90DR and RQBK45DR connectors also feature a special swivel design intended for dynamic applications, making installation easier.
Strain relief and distribution: To prevent conductors from being pulled out of the pins inside electrical connectors, the installation is stabilised using the RQM support system and its movable RQMR-MOVE inserts, which provide reliable strain relief. Branches and take-offs are created using dedicated RQT-PA / RQY-PA T- and Y-connectors and RQPRO-S protective covers.
Fire protection: All components used in this zone must comply with EN 45545-2 at the highest Hazard Level 3 (HL3), ensuring self-extinguishing properties, low smoke emission, and minimal toxicity.
2. Railway vehicle roof - resistance to UV radiation, wind, and high voltage
Roof-mounted installations, including the wiring of pantographs, switchgear, braking resistors, and HVAC units, are routed through complex structural systems. Although the amplitude of dynamic movement is lower here than in the coupling area, the installation remains fully exposed to harsh environmental conditions.
Risk analysis and selection criteria
The main issue is the photochemical degradation of plastics caused by direct UV radiation and exposure to ozone generated around high-voltage equipment. Conventional plastics quickly lose plasticisers, become brittle, and crack under the train’s natural vibration. The installation must also withstand wind pressure and driving rain at speeds of approximately 160-200 km/h, as well as aggressive high-pressure cleaning at service depots.
System solutions
UV- and thermal-shock-resistant components: ROHRflex PA 12+ and PA 12F+ polyamide conduits are also recommended for roof applications. Their modified structure provides complete resistance to sunlight, ozone, and major temperature fluctuations, from winter frost to radiative roof temperatures exceeding 80°C.
Stress-compensating fastening systems: Dedicated RQM supports used together with the RQMR-MOVE system are well suited for fastening conduits on the roof. This solution allows controlled longitudinal movement of the conduit, compensating for stresses caused by the thermal expansion of the roof structure and by structural vibration.
Long-term sealing performance: The installation is completed with RQGK / RQGKZA / RQGKST and RQGR connectors. Thanks to integrated seals and the FLEXAquick quick-installation system, a durable IP68 / IP69K protection rating is achieved, preventing moisture ingress and hazardous short circuits in high-voltage zones. The entire roof system complies with the requirements of the EN 45545-2 fire protection standard.
3. Underframe and bogies - protection against impacts, chemicals, and interference
The underframe zone, particularly the areas around bogies, traction motors, and braking-system sensors, is an environment dominated by severe mechanical and chemical exposure. In this case, the optimum solution is to replace conventional plastic corrugated conduits with heavy-duty hybrid and metal protection systems.
Risk analysis and selection criteria
Underframe wiring is constantly struck by ballast projected from the track at high force. It is also continuously exposed to gear oils, lubricants, hydraulic fluids, and winter road salt. Other major challenges include high-temperature zones around motors and brakes and increasingly stringent electromagnetic compatibility requirements due to the proximity of high-power cables.
System solutions
Mechanical armour and resistance to fluids: FLEXAgraff-PU-F hoses are recommended as the foundation of underframe protection. These are robust metal conduits with a polyurethane (PU) jacket. They provide uncompromising resistance to stone impacts and prevent the installation from being perforated. The polyurethane ensures full sealing performance from IP66 to IP69, is halogen-free, and offers complete resistance to oils, lubricants, and aggressive cleaning chemicals.
Extreme EMC protection: In areas adjacent to drives and inverters, where induced interference could distort signals from sensors such as wheel-speed sensors, the FLEXAgraff-CU-PU conduit system with USD-M connectors is recommended. Equipped with integrated copper braiding, the system creates a continuous shield that blocks electromagnetic waves while retaining full mechanical resistance and the external sealing performance of the PU jacket.
High-temperature zones: Specialised FLEXAhightemp thermal protective sleeves are used in the immediate vicinity of braking-system components or resistors, where operating temperatures rule out conventional materials. They provide continuous temperature resistance from -50°C to +350°C and short-term resistance up to 700°C, protecting the wiring against overheating and thermal degradation.
Sealed metal transitions: The entire underframe system can be integrated using robust brass USZ-M metal connectors, which ensure mechanical continuity of the armour and reliable sealing of the installation beneath the vehicle in compliance with EN 45545-2.
4. Wall penetrations and fire barriers - safety in accordance with EN 45545-3
Designing modern rolling stock requires not only the protection of cables against external influences but also the strict division of the vehicle into independent fire zones. Where an electrical installation must pass through partition walls or the car body structure, one of the key challenges for design offices is compliance with EN 45545-3, which defines the fire-resistance requirements for fire barriers.
Risk analysis and selection criteria
In the event of a fire, cable penetrations through structural barriers become natural bridges through which flames, heat, and toxic gases can rapidly spread to adjacent vehicle sections or passenger compartments. Conventional cable glands and protective conduits do not provide a sufficient barrier in such locations. Severely restricted installation space is an additional challenge in fire-barrier zones.
System solutions
Intumescent system (Fire Barrier): As a distributor of specialised solutions, we recommend using the Fire Barrier Adapter ADMF at penetrations through fire-resistant walls. This advanced engineering solution contains an internal insert based on intumescent graphite. When exposed to high temperature, the material expands to up to 40 times its original volume, completely sealing the conduit opening. This blocks the passage of fire, smoke, and gases for at least 30 minutes, corresponding to fire integrity class E30, and provides passengers with valuable additional time for evacuation.
Compact wall penetrations: Where the vehicle structure requires connections to be kept as short as possible and unnecessary bends to be eliminated, RQGKST connectors are an ideal solution. Their optimised, short geometry enables a protective conduit to be routed safely and tightly through a structural wall, saving valuable millimetres in densely packed spaces.
5. Passenger compartments and rapid service repairs
Cable installations routed inside the vehicle, beneath seats, inside side walls, in the driver’s cab, or in the ceiling space of the passenger compartment, have their own specific requirements. In addition to stringent fire-safety requirements, the priorities in these areas are low weight, flexibility, and ease of routing within tightly packed cable bundles.
Risk analysis and selection criteria
Internal wiring must be protected against mechanical abrasion from sharp edges of metal structures, while routing rigid corrugated conduits through narrow wall profiles is technologically difficult. From the perspective of repair and service facilities, including retrofit and refurbishment projects, replacing damaged protection beneath the train or on the roof is another major challenge. A conventional conduit replacement would require electrical connectors to be removed and the pins to be disconnected, resulting in high costs and extended vehicle downtime.
System solutions
Self-closing braided sleeves: Lightweight plastic textile sleeves such as HG-PET-SV are an excellent choice for passenger compartments. Their self-closing structure allows them to be installed quickly over existing, pre-terminated cable bundles without having to pull the wires through the sleeve. For conventional routing inside the vehicle structure, we also recommend lightweight ROHRflex PA 6 conduits, which combine optimum protection with the highest level of fire safety.
Repair systems requiring no disassembly: To eliminate costly service downtime, we supply a unique two-part split system consisting of ROHRflex DUO protective conduits and matching split RQG-DUO connectors. Thanks to their longitudinally split design, a new, fully functional mechanical and sealed protective system can be installed over a damaged section of the installation, for example beneath the underframe, in just a few minutes without disconnecting any electrical connections.
Summary - a holistic system approach
Practical design experience leads to one overriding principle: the hybridisation of components from different suppliers should be strictly avoided. Even a technically advanced protective conduit will not deliver the expected performance if it is combined with a random cable gland or an unsuitable connector. The technical problems and accelerated component wear resulting from such combinations will increase the total cost. In the long term, these costs may quickly exceed the short-term savings achieved by selecting cheaper components.
By designing cable protection around coherent, fully tested FLEXA systems consisting of a conduit, connector, and support, designers can be confident that every zone of the vehicle will retain its declared functionality over millions of kilometres. Moreover, the system approach significantly reduces installation time on the production line and simplifies the certification process for the entire vehicle by providing auditors with a complete and consistent EN 45545-2 HL3 fire-safety documentation package.
