When is the protection of the "dead-man" feature on a moving train lost?

The protection of the "dead-man" feature on a moving train is lost when the reverser is centered. The "dead-man" feature is a safety mechanism designed to ensure that the train operator is in control of the train at all times. If the operator becomes incapacitated or unresponsive, this mechanism requires the operator to keep a certain control lever in a specific position, usually forward or backward, to maintain control and allow for safe operation.

When the reverser is centered, it indicates that neither forward nor reverse power is being applied, which could lead to a loss of control. In this situation, the "dead-man" feature is ineffective, because there is no active manipulation of the controls by the operator, thus removing the safeguard intended to ensure continuous oversight of the train's movement.

The other options do not directly relate to the functioning of the "dead-man" feature in the same way. Releasing the brakes or cutting the power supply might affect the train's operation, but these actions do not inherently disable the protective function of the dead-man mechanism as does centering the reverser. Additionally, exceeding speed limits could necessitate control measures but does not directly impact the operator's control status through the dead-man feature.