An automatic transfer switch (ATS) is a device that automatically transfers a power supply from its primary source to a backup source when it senses a failure or outage in the primary source. When a failure occurs in a primary power system, the ATS invokes a standby power source, such as an uninterruptable power supply. An ATS can also start up more long-term backup power systems, such as local diesel generators, to run electric equipment until utility power is restored.