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.
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Since the ATS is connected to both primary and backup power sources, it serves as an intermediary between equipment and the power supplies, acting as an electrical relay. An ATS can also act as a redundant, rack-mounted power supply for equipment that is connected to a power source with only one cord.
In the data center, it is vitally important to have uninterrupted power. To achieve this goal, the systems in the power path must be properly maintained and tested. To ensure reliability in the event of a power outage, data center administrators need to routinely monitor the ATS. ATS units can channel considerable amounts of energy, which can put heavy stress on the electrical contacts involved, so regular maintenance is critical.
ATS vendors include APC, Dell, Cummins Power Generation, General Electric and Western Telematic. There are also manual power transfer switches that require a data center manager to physically flip a switch to transfer to a new power source, rather than switching automatically.