What condition prevents the door from closing when the drive arm and connecting link are in line?

The condition that prevents the door from closing when the drive arm and connecting link are in line is typically related to an electrical command, which involves the elevator's control system. In an electrically commanded scenario, the system relies on signals from sensors and controllers to ensure safe operation. This can include conditions where the doors are commanded to stay open due to safety protocols, such as when an elevator is at a floor and a sensor indicates that it is not safe for the doors to close, possibly due to an obstruction or an ongoing operation.

When the drive arm and connecting link are aligned, it indicates that the mechanical components are in proper position to close the door, yet an electrical signal may specifically instruct the system to keep the doors open. This can happen in various situations, such as during maintenance, testing, or if passenger safety sensors detect a potential hazard.

The other options refer to mechanical limitations, manual overrides, or physical obstructions, which do not inherently involve electrical commands. Each of those scenarios would lead to a different mechanism preventing closure, but in this case, it is the electrical command that dictates the operation of the door in relation to the drive arm and connecting link alignment.