Which device is represented by code Z?

• A. Contact rail alarm indicator light
• B. Exit push button stick repeater relay
• C. Contact rail indicating relay
• D. Bell

Answer: (C)

In signaling diagrams, letters are used to identify device types, and the letter Z is assigned to the contact rail indicating relay. This relay monitors the state of the contact rail—essentially the track connection used in the electric traction system—and feeds that status back to the control or interlocking circuitry. When the rail state changes (for example, rail continuity is broken or restored), the relay changes its contacts to signal that state to the system, helping control signals and routes accordingly.

That’s why this is the best match: the code Z directly corresponds to a contact rail indicating relay. The other options describe different devices—an alarm indicator light for faults, an exit push button repeater relay for duplicating push-button signals, and a bell for audible notification—which are not what the code Z represents.