What are "back-up power systems" used for in elevators?

Back-up power systems in elevators are crucial for ensuring continued operation during power outages. These systems typically include batteries or generators that activate automatically when the main power supply is interrupted. By providing power to the elevator, these systems allow it to operate safely, enabling passengers to exit the elevator without being stranded. This reliability is especially important in buildings where elevators are essential for accessibility or in emergency situations.

The other choices relate to functionalities that back-up power systems do not influence; they do not affect speed, spatial capacity, or weight control directly. Back-up systems focus specifically on maintaining operational integrity and safety in the event of electrical disruptions.