There are a number of installations in the rail industry where the loss of power or data could have serious safety consequences, and the least of these is severe disruption of services. Carriage interiors, areas above and under carriages, and intercar jumpers and couplings must withstand a number of cabling hazards, which might include immersion due to flooding, dust penetration in tunnels, the risk of cable theft, and the ongoing possibility of vibration working connections loose. These scenarios necessitate the need for a high-performance fitting that, when paired with the correct conduit, protects against all of these risks and more for the lifetime of an installation. Proper rail industry fittings can manage and control risks and mitigate costly downtime.
Cable protection and its secure interface with equipment is vital. When specifiers consider the lifetime costs of a cable protection system, including maintenance and the potential loss of revenue due to service outages on track, in rolling stock, or in stations, lasting performance is essential.
Key considerations for cable protection include ingress protection (IP) ratings, fire performance, vibration and shock resistance, and chemical and abrasion resistance. Luckily, technological and engineering advancements, namely in the areas of connectors and fittings, are helping railcars better deal with harsh conditions.
Safety and standards on the railway
To ensure passenger safety and operational integrity, fittings must be subjected to detailed quality auditing in the manufacturing process, including the International Railway Industry Standard (IRIS). IRIS Certification is an efficient, transparent system used to audit rail industry suppliers, replacing the need for individual management system evaluations by the four founders of the initiative (Alstom Transport, AnsaldoBreda, Siemens Transportation Systems, and Bombardier Transportation).
The globally recognised rail industry quality standard, IRIS rev.03 is based on the ISO 9001:2015 structure, the world’s leading quality management system standard, and adds railway-specific requirements. By holding IRIS Certification, companies demonstrate competence in supplying the railway industry with a broad range of systems that meet rigorous application demands.
Why is Ingress Protection (IP Rating) so important?
Cable protection is critical for demanding applications where continuity of supply, performance and safety is essential. Flooding is one of the most extreme hazards for electrical systems. If products are submerged in water, Ingress Protection of the fitting/system is of utmost importance. The higher the IP rating, the more protection there is against contaminants entering the system. Ingress Protection is normally tested using EN IEC 60529 with the levels of protection designated by a 2 digit code. The first digit signifies protection against solid objects and dust. The second digit designates protection against water. IP tests to EN IEC 60529 give an indication of system performance, but are short tests conducted in ideal laboratory conditions, at room temperatures and in straight lengths. This isn't always a realistic application. Therefore, many applications require ‘over and above’ standard IP tests.
To validate product performance, look for a manufacturer that has met these environmental demands by undergoing more than 1000 individual Ingress Protection tests and meeting IP66, IP67, IP68, and IP69 performance.
Fire protection for rail
The challenge of reducing fire casualties is to employ the proper protections and equipment so that a fire does not pose additional hazards such as toxic fumes or smoke. A connector should maintain low fire hazard properties, including flame retardancy, enabling low smoke emissions and toxicity, and be halogen-free. Just as there are various procedures and codes to reduce the risk of fire, there are numerous tests and measures used to qualify as a low fire hazard product.
Flame Retardancy: To assess how flame-retardant a material is, the defined test method is to measure the Limiting Oxygen Index (LOI) according to BS EN ISO 4589-2, which determines the percentage of oxygen that needs to be present to support combustion. The higher the LOI percentage, the greater the flame retardancy of the material. A normal oxygen level is approximately 21%.
Smoke: A specified sample of material is burned under controlled conditions in a smoke chamber, and the smoke observation of a defined beam of light is measured. The lower the smoke density, the more efficient evacuation and safety becomes.
Toxicity: A specified sample of material is burned under controlled conditions in a smoke chamber, and the fumes are analysed for various gases. The concentration of each gas is then multiplied by its toxic potency to give a toxicity index. Although toxicity and smoke tests are similar, the results and the requirements are different. If halogen, sulphur or phosphorus is present, the material is unlikely to pass the low toxicity test.
Halogen-Free: Halogen-based materials give off highly toxic fumes and often thick smoke. A material cannot be considered as low fire hazard if it contains halogen. However a halogen-free material is not necessarily low fire hazard as it must also be low-toxicity, low-smoke, and highly flame-retardant. Halogen content is assessed by various chemical tests and analytical techniques.
Fittings and connectors should also comply with the strictest of rail industry standards, including NFPA 130, which specifies fire protection and life safety requirements for underground, surface, and elevated fixed guideway transit and passenger rail systems to ensure safety.
Vibration and shock resistance
Moving railcars are constantly exposed to vibration hazards during regular operation. The proper fittings and connectors can help offset this risk by providing anti-vibration performance that has been tested to and complies with EN 61373 Railway Applications for Rolling Stock Equipment. EN 61373 tests conduits against vibration and shock, ensuring that system integrity is maintained. Additional tests can be run for fatigue life on systems that have constant motion such as intercar jumpers. This fatigue life test subjects the system to one million cycles, representing 35 years of service life. Assuming that there are no signs of failure during the tests, it shows that the products can exceed one million cycles.
Specifiers, installers, and contractors rely on tensile strength to ensure the integrity of the system when there is a lot of motion, vibration, and pulling on the connector. Tensile strength is the maximum stress that a material can withstand while being stretched or pulled before breaking. Connectors should offer a superior tensile and impact compression strength. Look for a fitting with all-round teeth to provide anti-vibration protection together with a high pull-off strength (up to 154 pounds).
The rail industry is a technically demanding sector that presents numerous challenges when it comes to product performance and compliance to global standards. To position your operations for success, find a supplier that partners with you on material technologies and industrial design to manage and control risk, make procurement more efficient, and continuously strive for improved operations.
Authored by Frank Ball at Flexicon.