What effect occurs when the auto coupler control MCB trips?

When the auto coupler control MCB (Miniature Circuit Breaker) trips, it activates the emergency brake on every car involved in the train system. This is a safety mechanism designed to prevent further movement and potential accidents, ensuring that all cars come to a stop when an issue arises in the auto coupler control system. The activation of the emergency brake in all cars provides a comprehensive safety response, mitigating risks that can arise from an uncontrolled situation.

In this context, the other options do not accurately reflect the functionality of the system when the MCB trips. For instance, while it might seem reasonable that some functions may still operate, the emergency brake is universally applied for safety. Thus, the correct response denotes a system-wide precautionary measure initiated by the trip of the auto coupler control MCB.