What happens when the door close and locked loop MCB is tripped?

When the door close and locked loop MCB (miniature circuit breaker) is tripped, it indicates that the system is experiencing a fault condition that affects the door operation and safety. In such instances, all the described outcomes become relevant.

If the doors are open when the MCB trips, there is typically a mechanism that may cause the doors to attempt to close automatically to ensure safety and compliance with operational protocols. The blue door light may flash to signal a warning that the doors are moving or an issue with the door locking system exists.

In the case that the doors are already closed at the time of the trip, it's common for the indicator lights to not illuminate, as the system may interpret that everything is secure despite the fault from the MCB.

Furthermore, when the MCB has tripped, there may be safety protocols that require the operation of the train and bypass doors to be performed manually. This manual operation is a safeguard to ensure that personnel can exit the train or access different train sections safely without relying on potentially faulted automated systems.

Therefore, option D encompasses all these scenarios, capturing the comprehensive nature of operations and safety mechanisms in response to a tripped door close and locked loop MCB.