Automatic Transfer Switch (ATS) is used which operation voltage is no more than 660VAC, and may transfer with load. The ATS rated current series is40A, 63A, 80A,125A, 160A, 250A, 400A, 630A, 800A,1000A,1250A,1600A,2000A,be divided up two types with 3 poles and 4 poles. The ATS of 40~125A is defined with ‘N’; 160~400 is defined with‘T’; 630A~2000A is defined with “M”.