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How to specify the right communication cables for train cars for mechanical, physical, and electrical requirements

New generation train cars use communication cables and data protocol such as CAT 5E, CAT 6, CAT 7, MVB (Multifunction Vehicle Bus), WTB (Wire Train Bus), RS-485, LON (Local Operating Network), RS-422 and Canbus demanding 30-40 years in harsh environment.  As long as the electrical characteristics are achieved (like impedance and cross-talk), the cable can be made in different AWG sizes and materials for the conductor, insulation, shields and jacket.

When designing a communication cable for train cars environment, the following shall be considered

- Stranded conductor needs tol survive vibration and torque. The use of solid conductor should be avoided.
- Cross linked thermoset insulation and jacket should be preferred over thermoplastic materials. The cross-linked material is better in abrasion, cut through and notch propagation.
- The shield should be made of Tin Copper braid with an optional addition of an Aluminum/Mylar tape. The braid shield make the cable ruggedize with great resistance to crush and rough installation practices.

Other critical attribute is the capability of the cable to withstand temperature cycling and extreme hot or cold temperatures as the train exit out of the tunnel or parked and operated outdoors.

In addition to the mechanical, physical and electrical requirements of the communication cable, it needs to comply with local specifications for Flame, Smoke and Toxicity. (FST).   (Please refer to my other Blog regarding FST by visiting the RSCC Blog site)

To learn about communication cables for train cars FST requirements, please search the blog on the www.r-scc.com web site.

Communication cables for train cars can be different in construction, size and materials but they need to comply with NFPA 130 and other local codes as apply for a specific project. Train cars communication cables include CAT 5E, CAT 6, MVB (Multifunction Vehicle Bus), WTB (Wire Train Bus), RS-485, LON (Local Operating Network), RS-422 and Canbus.

FST is an abbreviation of Flame, Smoke and Toxicity and is used in local train cars specifications.
The Flame requirement includes two tests, NFPA 130-2017 and 49 CFR part 238, Appendix B.

Chapter 8 of NFPA 130-2017, NFPA 130-2014 and NFPA 130-2010 specifies that all cables including communication cables for train cars shall pass the UL 1685 with FT4/IEEE 1202 flame method. UL 1685 is a large scale flame test and the cables are bundled as specified. During the 20 minutes vertical flame test, the total smoke and peak smoke are measured and needs to be below a specific value to pass the test.

The 49 CFR part 238, Appendix B. is a small scale flame test that is done on a single cable per NEMA WC 3/ICEA S-19-81, paragraph 6.19.6. The test includes 5 applications of 15 seconds flame with 15 seconds rest. The flame propagation and monitored to a specific height and ignition of cotton under the sample.

The Smoke requirement is a small scale test of ASTM E662 that is done on the finished cable. The test is conducted in flaming and non-flaming modes with specific values after 90 second, 4 minutes and 20 minutes.

• Please note that UL 1685 has a smoke measurement test that needs to be satisfied.

The Toxicity test is specified as BSS 7239 per Boeing standard. The test is done in a smoke chamber and the various gases are measured by tubes. The gases includes Carbon Monoxide (CO), Hydrogen Fluoride (HF), Nitrogen Dioxide (NO2), Hydrogen Chloride (HCL), Hydrogen Cyanide (HCN), Sulfur Dioxide (SO2).

Local specification list the maximum ppm value per gas.

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