Communication optical cables are an important part of rail transit locomotive cable systems and communication systems. The safety, stability, and service life of cable materials directly affect the long term reliable operation of the whole system. For this reason, the use of low smoke zero halogen materials LSZH and crosslinked polyolefin materials continues to increase in rail transit locomotive cables and rail transit communication optical cables. These materials are now becoming mainstream solutions.
The operating environment of rail transit locomotive has clear characteristics. Stations, tunnels, locomotive interiors, and trackside equipment areas are mostly enclosed or semi enclosed spaces. If a fire or electrical failure occurs, smoke and harmful gases from cables can seriously affect passenger evacuation, emergency response, and the integrity of communication systems. Because of this, rail transit standards in many countries require strict low smoke, halogen free, flame retardant, and environmentally friendly properties for materials used in locomotive communication optical cables.
Many public accident reports show that in enclosed space fires, smoke is the main cause of injury and poor visibility. Based on this fact, standards such as EN 50264, EN 50306, EN 50305, EN 61034, EN 60754, and EN 45545 clearly define limits for smoke density, toxic gas release, and flame retardant performance of rail transit communication optical cables. In real projects, station communication cables, tunnel communication cables, and onboard communication cables widely use LSZH materials as the basic sheath system.
During long term operation, rail transit communication optical cables must meet several key requirements. The first is flame retardant and low smoke performance. Optical cables are often installed in bundles on trays, ducts, and equipment areas. If a local fault happens, the material must limit flame spread along the cable and keep good light transmission during burning. This helps evacuation and rescue work.
The second requirement is halogen free and low corrosion performance. Rail transit systems include many communication devices, control units, and metal parts. If cable materials release halogen acid gases during burning, serious corrosion can occur. This increases repair and replacement costs after accidents. LSZH materials release almost no halogen acid gases during burning. This helps reduce damage to the system.
In addition, communication optical cables must have good mechanical strength and environmental resistance. Under tunnel vibration, temperature changes, humid conditions, and long term service, the material must stay flexible, resist cracking, and keep stable size. This protects the optical fiber structure. For regular rail transit locomotive cables, materials also need oil resistance, abrasion resistance, and low temperature performance.
Within LSZH material systems, crosslinked polyolefin has become a key material for rail transit locomotive cables. Compared with normal thermoplastic polyolefin, crosslinked polyolefin forms a stable three dimensional network between molecular chains. This greatly improves heat resistance, mechanical strength, and long term aging stability.
In rail transit communication optical cables, LSZH crosslinked polyolefin is usually used for outer sheaths or functional sheath layers. Its long term working temperature can stay above ninety degrees Celsius. Under heat from train operation and heat buildup in tunnels, the material keeps its structure without softening, flowing, or performance loss.
The crosslinked structure also improves resistance to stress cracking. Under repeated vibration, bending, and temperature cycles, the sheath is less likely to crack. This is very important for communication optical cables. Once the sheath is damaged, moisture and pollutants can enter and affect long term optical fiber safety.
Rail transit communication optical cables are often installed together with rail transit locomotive cable systems. They form an integrated wiring network inside locomotive and equipment areas. Because of this, material consistency and safety level alignment are very important.
At present, many rail transit locomotive cables also use LSZH crosslinked polyolefin as insulation or sheath material. This creates a unified low smoke, halogen free, and flame retardant performance between communication cables and locomotive cables. In fire conditions, the system shows a consistent safety response.
LSZH crosslinked polyolefin does not contain halogens and has low risk of plasticizer migration. It works well with onboard communication equipment and optical modules. This supports stable long term system operation. Its good processing stability also suits continuous extrusion of complex structures and thin wall communication optical cables.
In rail transit projects, material selection strongly depends on standards and engineering rules. EN 45545 is now a key international fire protection standard for rail transit. It defines clear levels for smoke density, heat release, and toxic gas emission of cable materials. Urban rail transit and high speed rail projects in China are also adopting similar technical requirements.
In real engineering use, station communication cables, tunnel communication cables, onboard communication cables, and trackside signaling systems all widely use LSZH crosslinked polyolefin materials. Long term operation has proven their safety and stability.
As rail transit systems expand and train density increases, requirements for communication cable safety level and service life continue to rise. LSZH materials have moved from recommended options to basic configurations.
In future rail transit communication systems, material systems based on LSZH low smoke zero halogen crosslinked polyolefin will continue to hold a main position in communication optical cables and rail transit locomotive cables. Their combined advantages in safety, durability, environmental resistance, and engineering reliability make them a stable long term choice for the rail transit industry.
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