Which device prevents an interlocking appliance from being operated?

The choice indicating that an approved device applied to the control console prevents an interlocking appliance from being operated is correct because it highlights a key safety measure used in railway operations. Interlocking systems are designed to ensure that signals and track switches function safely and prevent conflicting movements of trains.

An approved device at the control console serves as a safeguard, providing operator control and confirmation that specific conditions are met before the interlocking appliance can be activated. This could include things like locks, switches, or indicators that signal whether it is safe to change signals or routes. By requiring authorized input or a specific device, the system minimizes the risk of human error or unauthorized activation, thereby enhancing safety and operational effectiveness.

The other choices do not serve the same critical function. Random signals from the OCC could lead to confusion or operational errors, as they may not be based on the specific situational context at the interlocking. Manual input from the operator is essential for activating interlocking systems, but it can also introduce the possibility of mistakes unless there are appropriate checks in place. Emergency safety mechanisms, while vital for safety, operate as a response to alarms or unsafe conditions, rather than as a preventative measure against operation in the first place.