High Standards for High Speeds
By Lane Latto, Bishop & Associates Inc.

Countries around the world are investing in their rail networks, particularly in high-speed passenger rail. That means new opportunities for connector manufacturers — who must adhere to standards to meet safety and performance goals.

Connector solutions arise from the need to resolve specific, challenging situations and provide consistency and compatibility for providers and consumers. These solutions then become standards, which govern aspects of the application well into the future. One such standard has had a significant impact on the modern global rail industry. The Union of International Railways (UIC), Train Communications Network standard, established for time-critical and safe on-board communication, encompasses IEEE 1473 protocols and uses an established connector set interface, creating the Wire Train Bus (WTB).

There are three main types of communication that are supported by the WTB: telecontrol, diagnostics, and passenger comfort. Telecontrol encompasses train functions such as traction control, door operation, lights, heat, and tilting for high speed. The diagnostic component monitors and reports such information as equipment failure and maintenance information. Passenger comfort encompasses the public address system, providing general information announcements such as next station, connections, and system delays, along with the electrical outlets within the train carriages.

The WTB wiring scheme is based around a 13- pole connector system, which terminates a multi-core cable comprised of shielded pairs and power conductors. Initially, the UIC- specified cable contained 13 individual conductors or cores, but that has now been expanded to 18. The jacket of this cable is of “zero halogen” composition in order to satisfy the passenger safety specifications of many of the operating rail companies.

The original 13-circuit connector was physically large enough to accommodate extra circuits and has been expanded to a total of 18. The 18 circuits have been arranged in such a way as to mate with the original 13-circuit version for full backward compatibility.

This connector system is designed with crimp terminations around a 3mm diameter screw-machined pin-and-socket system intended for hand termination to 18 AWG wire. Generally the connectors have die-cast aluminum bodies, a “breakaway” feature, and are rated for 10 amp current carrying per contact. This connector set is sometimes identified as UIC 558, while the cable is described as UIC-18 or UIC-13 in manufacturers’ product offerings.

The UIC cable and connector was first introduced along with the specifications for carriages built according to the UIC type Y (24.5 meters long, 8 cabins) and the UIC type X (26.4 meters long, 10 cabins), but has recently been used for a variety of other passenger carriages, allowing mixing of InterCity (medium to long distances) and regional (short to medium distances) carriages. Typically, there are two redundant 18 core WTB jumper cables used per carriage interface.

Integral to the WTB concept is the creation of a standard interface for plug compatibility between equipment on-board rail vehicles. This compatibility feature is referred to as the Multifunction Vehicle Bus or MVB. (See picture above for an example of this interface.)

The MVB interface is a typical 9-pin subminiature D connector usually supported by a die-cast metal cable clamp/shell. Examples integrated into rail control equipment are highlighted above.

The actual connector components that support WTB and MVB are produced by Harting, Deutsche, and Schaltbau, as well as many other suppliers. Look to Huber & Suhner, Nexans, and others for the UIC-18 cable.

This IEEE communication network was championed through the collaboration of both operating railways and key manufacturers. The contributing rail operators are established in countries such as Spain, Germany, France, Poland, Italy, the Netherlands, and China. The participating key manufacturers, such as Alstom, Bombardier, Siemens, Mitsubishi, CAF, and others, compete at a global level, proposing WTB compatible systems for railway operators on all continents. 

As the Wire Train Bus has global implications, one can expect to find the UIC 558 connector and cable standard, described above, in use for many platforms in production today. This standard has become a key part of designing for the rail industry, and as high-speed rail extends into new markets throughout the world, particularly in China and Europe, opportunities for connector manufacturers will expand as well.