What does it indicate when emergency power is feeding the signal mains?

When emergency power is feeding the signal mains, it indicates that the transfer switch is in the D energized position. This position is specifically designed to switch the power source from the primary (normal) supply to emergency power, which ensures that the signal system remains operational during a power outage or failure.

In this case, the energized position signifies that the system is currently utilizing the emergency power source to maintain functionality. This is crucial for the safety and reliability of transport systems, as it ensures that signals and communications remain active even under adverse conditions. The understanding of transfer switch positions is vital in electrical systems to ensure that power sources are effectively managed, particularly in emergencies.