For emergency power in buildings or other circumstances, Auto Transfer Switch (ATS) is essential. ATS can automatically transfer load between the main power and the emergency power (generating set) without the operator. When the main power fails or the voltage drops below 80% of normal voltage, the ATS will start the emergency generating set after a preset time of 0-10 seconds (adjustable), and transfer the load to emergency power (generating set). Contrarily, when the main power recovers to normal level, the ATS will transfer the load from the emergency power (generating set) to the main power, and then stop the emergency power (generating set).