How are Emergency Lights powered and how long do they last?

How are Emergency Lights powered and how long do they last?

• A. One battery charged from external power and lasts 5 minutes
• B. Three batteries charged from standby power and last 15 minutes
• C. Four batteries charged from the emergency buses and last at least 10 minutes
• D. Four batteries charged by the main buses and last 60 minutes

Answer: (C)

Emergency lighting must stay on when main power is out, using independent power sources that guarantee illumination for a minimum duration. The setup uses four batteries that are charged from the emergency power buses, so they remain ready even if the normal electrical system fails. When power fails, those batteries provide the lights for at least 10 minutes, giving passengers a safe path to exits. That explains why four batteries tied to the emergency buses is the correct arrangement. It delivers redundancy and the required runtime without relying on main power. The other options don’t fit because they either reduce redundancy, rely on the wrong power source, or state a longer duration than what these systems are designed to provide.

Emergency lighting must stay on when main power is out, using independent power sources that guarantee illumination for a minimum duration. The setup uses four batteries that are charged from the emergency power buses, so they remain ready even if the normal electrical system fails. When power fails, those batteries provide the lights for at least 10 minutes, giving passengers a safe path to exits.

That explains why four batteries tied to the emergency buses is the correct arrangement. It delivers redundancy and the required runtime without relying on main power. The other options don’t fit because they either reduce redundancy, rely on the wrong power source, or state a longer duration than what these systems are designed to provide.