Power Supply Unit Operation; Power Over Ethernet Power Supplies - IBM 4002-Y2A Installation And User Manual

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AC power receptacle

Power supply unit operation

When only one PSU is installed, both "AC OK" and "DC OK" LEDs on the
installed PSU must be green for the y-series device to function normally.
When two PSUs are installed, both "AC OK" and "DC OK" LEDs for one of the
installed PSUs must be green for the y-series device to function normally.

Power over Ethernet power supplies

The 4002-Y2B and 4002-Y4B devices use a 620W PSU. When one PSU is powering
the switch, the PoE budget is 410W. If both PSUs are installed and powering the
switch, each PSU provides 410W to the switch, increasing the PoE budget to 820W.
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Ethernet y-series Installation and User Guide: Installation and User Guide