Advancements in Rail Connectors
By Mike Gardiner, Product Manager, ITT Interconnect Solutions

A connector’s design and the materials used in its manufacture directly impact the performance and reliability of the component. Connectors designed for use in harsh environment, safety-critical rail applications are required to perform consistently and reliably regardless of shock, vibration, high pressure, extreme temperature, and other harsh environment conditions. Many rail customers are seeking smaller, lighter, more dynamic solutions that meet the rail industry’s stringent performance and durability specifications. Recent design and material developments have enabled advancements in connector technology that meet these demanding performance and environmental parameters for rail applications.

Rail Requirements: Rugged Connectors
The rail industry has strict safety-critical design parameters that must be met when sourcing connectors, including size, voltage specifications, and resistance to environmental elements. The ability to withstand temperature fluctuations is also a significant concern, particularly in under-car applications such as traction, motor, and brake controls, where cables and interconnects can experience temperature extremes. In addition, rail connector solutions must be flame-retardant. High-temperature connectors are often constructed with machined copper alloy-plated contacts and a machined stainless steel shell with ceramic inserts. Conventional connector inserts are constructed with plastic or rubber, but these materials melt under the extreme temperatures present during a fire. Ceramic is resistant to fire and brittleness caused by moisture evaporation, and the rigidity of ceramic material makes it less susceptible to vibration and breaking. A ceramic insert is kept in place in the shell by the use of a metal retention ring. As a result, the connector is easy to disassemble, allowing for quick, simple field maintenance and service.

While materials like neoprene are suitable for temperatures ranging from -55°C to +25°C, connectors utilizing silicon are capable of operation from -55°C to +200°C. Furthermore, some connectors are designed to meet European CEN/TS 45545 standards governing railway fire safety, and thus must be capable of withstanding high temperature exposure of at least 15 minutes on the ISO 834-1 heating curve, where the maximum temperature is 800°C. Connectors that feature reverse bayonet coupling have been proven to meet the European CEN/TS 45545 standards and withstand temperatures up to 800°C for the allotted time, making them ideal for use in safety-critical rail applications, such as electronically controlled pneumatic (ECP) braking and engine diagnostic controls.

Rail connectors require resistance to high pressure, corrosive liquids, and gases, in addition to high temperatures. The development of thermosetting elastomeric materials and PEEK (Polyether ether ketone) engineered plastics achieve the required environmental tolerances while yielding smaller and lighter circular connector solutions. For example, ITT’s VBN Series connectors are formed from thermoplastic material in accordance with NFF16-101 – NFF16-102 standards, and are available in sizes as small as three inches in diameter with the appropriate reductions in weight, associated with this dimensional envelope. The connector’s coupling gasket and other parts are made from silicone rubber and flame-retardant rubber, while the metallic parts of the connector are comprised of RoHS-compliant aluminum alloy with black epoxy-urethanic varnish. Connectors that feature IP67 sealing to withstand harsh environments can be specified for applications ranging from dashboard signal and power interfaces, to air conditioning and junction boxes.

Rail Requirements: High-Speed Connectors
Cost, functionality, and performance are also critical parameters for rail customers to consider, in addition to ruggedness and reliability. Designed to reduce costs and increase functionality in mass transit applications, manufacturers have developed connector solutions that bundle multiple Ethernet and MVB lines into a single connector. These high-speed circular bayonet databus connector solutions decrease the component and line count, reduce cost and weight, and increase functionality and performance. The high-speed connectors meet high durability and reliability specifications, and thus, are capable of meeting the requirement for high mating cycles.

One such solution, ITT’s CIR-M12 connector (right), provides reliable data transmission between rail cars and enables a variety of different data types (including Ethernet, MVB, WTB, and video signals) to be transmitted between cars in mass transit systems. The connector system is comprised of innovative QXM12 contacts mounted into their proven FRCIR Series connector circular bayonet hardware. Four conductor wires and the associated braid from shielded cables are integrated into the QXM12 contact, and a special plastic insert channels multiple QXM12 contacts and their cables into a singular connector.

This technology allows designers to incorporate data transfer from Ethernet, MVB, WTB, and video lines according to VG95234 (where applicable), within the same connector, handling data feeds from diverse sources such as engine diagnostics, brake controls, environmental conditioning, passenger display systems, networking, and lighting control. The databus connector contacts are rated at three amps (maximum current for 1ms is 10 amps), while operating voltage is 100Vdc and insulation resistance is 10GΩ. Mechanically, the insert conforms to UNI-CEI 11170 (I2F2) and UL94-V0 specifications.

Rail Standards
Worldwide standards for rail applications differ from country to country. This is particularly true for DIN rail specifications. IRIS (International Railway Industry Standard) certification is a globally recognized certification that qualifies component manufacturers to work with railway equipment manufacturers, system integrators, railcar assemblers, and their suppliers. IRIS was created to develop and implement a global system with uniform language, uniform assessment guidelines, and mutual acceptance of audits for the evaluation of companies supplying to the railway industry in order to create a high level of transparency throughout the supply chain. 

Engaging with a connector manufacturer that is experienced in each of these areas takes the guesswork out of designing for high temperatures, high-pressure interfaces, and myriad of other design challenges. Because these parts are being used in critical applications, customers do not want to be part of the suppliers’ learning curve—to maintain high levels of quality and performance, and avoid dangerous results, they want parts from a manufacturer with a proven track record.

Working with a manufacturer who is familiar with meeting the testing parameters of regulatory and standards bodies further streamlines design and development processes, while ensuring the connectors meet all necessary regulations. In-house testing capabilities, as well as continuous quality improvement programs, further reinforce a connector manufacturers’ position as a proven rail connector source.

Constantly exposed to high shock, vibration, pressure, and temperature conditions, as well as fluctuating environmental factors, rail connectors must be robust enough to endure these harsh environment conditions and operate properly at all times. Customers must select connectors designed specifically for harsh environment applications. To ensure a durable and reliable connector with high-performance characteristics that meets cost and functionality requirements, it is essential to develop a relationship with a connector company that is experienced in designing for harsh environment applications, and that is familiar with testing to the rail industry’s regulatory parameters.

Mike Gardiner is a product manager at ITT Interconnect Solutions, and has more than 30 years of experience in the connector industry. Mike received his B.S. degree from Saint Louis University. Mike can be reached at mike.gardiner@itt.com.