ZX corresponds to which device?

• A. Bell
• B. Contact rail indicating relay
• C. Contact rail alarm indicator light
• D. Contact rail alarm bell

Answer: (D)

In signaling diagrams, certain two-letter codes label the devices used. ZX is the symbol for the contact rail alarm bell. This audible device sounds an alert in the signal room or maintainer area when the track circuit (the contact rail) is in a fault or abnormal condition, providing immediate notification.

This is why the alarm bell is the best fit for ZX: it represents an audible alert as part of the track circuit fault indication, whereas the rail indicating relay is a relay that provides a visual or electrical indication to a panel, and an alarm indicator light is a visual cue. The bell serves the purpose of quick, urgent notification in environments where a visual cue alone might not be as effective.