HP Power over Ethernet (PoE/PoE+) Planning and Implementation Guide

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Planning and Implementation for the HP 2520 and HP 2520G Switches
Planning the PoE Configuration
found on a product’s data sheet). Adjust this total maximum power figure by
adding 16% to account for possible line loss. This value must be less than the
maximum power available shown in the table for your configuration.
Remember these switches use a single internal power supply which provides
two isolated output voltages for switch and PoE functionality. One supply
voltage provides power for the switch functionality while the isolated voltage
provides power for the PoE functionality. If either voltage fails, the entire
power supply shuts down disconnecting all switch and PoE connections.