The Voice of the Train: UIC Leaflet 568 and PA Interoperability

What is UIC Leaflet 568?

UIC Leaflet 568, titled “Loudspeaker and telephone systems in RIC coaches,” is the technical standard that ensures a train conductor can make a voice announcement that is heard in every carriage of an international train, regardless of which country manufactured the coaches.

In the era of cross-border rail travel (RIC – Regolamento Internazionale Carrozze), it is common for a train to be composed of a German locomotive, Austrian passenger coaches, and a Swiss dining car. Without a standardized interface for the audio signals, the Public Address (PA) system would fail at the first coupling. UIC 568 defines the electrical characteristics, pin assignments, and voltage levels for the 13-conductor cable that carries these analogue audio and control signals throughout the train.

Key Technical Specifications

The leaflet specifies an analogue transmission system designed to be robust over long distances (trains up to several hundred meters long).

1. The 13-Conductor Cable

The physical backbone of UIC 568 is the 13-wire bus. Each wire has a strict assignment to ensure compatibility:

• Loudspeaker Lines (Pins 1-4): Carries the audio signal for announcements and background music.
• Service Telephone (Pins 5-8): Allows for a private, point-to-point analogue voice connection between train crew members (e.g., the chef in the dining car calling the conductor).
• Remote Control (Pins 9-13): Historically used for synchronizing lighting controls or triggering specific automated announcements.

2. Voltage Levels

To prevent signal degradation over long cable runs, UIC 568 typically mandates “high voltage” audio lines (often 100V line systems). This is similar to professional stadium PA systems, where higher voltage allows for thinner cables and less signal loss compared to standard low-voltage consumer audio.

3. Priority Logic

The standard includes a “priority” mechanism. If background music is playing, a conductor’s announcement must automatically mute the music (ducking). Furthermore, an emergency broadcast from the locomotive driver overrides all other audio inputs. UIC 568 defines the control signals required to trigger these overrides across different vehicle brands.

Comparison: UIC 568 (Analogue) vs. Modern Digital Systems

While UIC 568 remains the baseline for compatibility, modern fleets are moving toward digital solutions. The table below illustrates the technological shift.

Relationship with UIC 558

UIC 568 is often confused with UIC 558 (“Remote control and data cable”).

• UIC 568 is primarily for Audio (PA and Intercom).
• UIC 558 is primarily for Door Control and Lighting control (and later, data transmission).

In many older international trains, you will see two distinct cables connecting the coaches: the 18-pole control cable (UIC 558) and the 13-pole audio cable (UIC 568).