Which of the following devices commands the backup generator to start based on monitored voltage?

The correct answer is the automatic transfer switch (ATS), which is a device designed to monitor the utility power supply and automatically switch to a backup generator when it detects a loss of voltage or drops below a specific threshold. The ATS plays a crucial role in ensuring that power is maintained even during outages by seamlessly transitioning from the primary power source to a secondary generator source.

When utility power is interrupted, the ATS sends a command to the backup generator to start, ensuring that there is no significant downtime in power supply. This mechanism is essential for critical applications, such as hospitals or data centers, where any interruption in power could lead to significant consequences.

Other devices, such as a transfer switch (TS), typically require manual intervention or do not automatically start the generator based on voltage monitoring. An uninterruptible power supply (UPS) provides short-term power during outages and does not command a generator. Circuit breakers protect electrical circuits from overloads but do not have the capability to start generators based on voltage conditions.