Explain the purpose and operation of an automatic transfer switch (ATS) in an emergency lighting system.

An automatic transfer switch (ATS) in an emergency lighting system is a device that automatically switches the power source for the emergency lights from the normal power source to an emergency power source, such as a generator or batteries, when the normal power source fails. The purpose of the ATS is to ensure that the emergency lights remain illuminated during a power outage, providing essential lighting for safe evacuation and emergency operations. In normal operation, the ATS monitors the voltage and frequency of the normal power source. If the ATS detects a failure in the normal power source, such as a voltage drop or a complete loss of power, it automatically switches the power source for the emergency lights to the emergency power source. This switchover typically occurs within a few seconds, ensuring minimal interruption of lighting. The ATS typically has two power inputs: one connected to the normal power source and one connected to the emergency power source. It also has an output that connects to the emergency lighting circuits. The ATS uses sensors and control logic to determine which power source is available and acceptable. When the normal power source is restored, the ATS automatically switches the power source for the emergency lights back to the normal power source. The ATS also typically includes features such as test switches and indicators to allow for periodic testing and monitoring of the system's operation.