The Cisco WS-CAC-4000W-INT is the 4000 W AC-input power supply designed for use with the high performing Catalyst 6509-V-E Switch. All Catalyst 6500 series AC-input power supplies, including the WS-CAC-4000W-INT, require single-phase source AC. Source AC can be out of phase between multiple power supplies or multiple AC-power plugs on the same power supply because all AC power supply inputs are isolated. This is the international component. Users in the United States should purchase the WS-CAC-4000W-INT.