HP ProCurve 2520 Planning And Implementation Manual page 107

Planning and Implementation for the 3500 Switches
Planning Your PoE Configuration
It takes 369.6 watts to fully provision 24 ports (plus 5 watts to account for load
fluctuations), leaving 1.4 watts to be returned to the pool of available watts.
This can then be added to the 22 watts held in reserve for the bank of ports
25-48, giving a total of available watts of 23.4 watts.
Since a port requires 17 watts to power up a device, there is enough available
power to power one more device in a port, somewhere between ports 25-48,
providing 25 powered ports.
You could also load balance or split the number of devices and wattage
between the two banks of ports. The 398 watts would be divided in half; 199
watts would be allocated to ports 1-24, and 199 watts would be allocated to
ports 25-48. There could be 12 devices on the bank with ports 1-24, and 13
devices on the other bank of ports, 25-48.
Both of these examples use maximum device wattage. If however, devices
using lower wattages are connected there could be more devices connected
to the switch than shown in these examples. Each environment will be
different.
Configuring the CLI threshold command sets a threshold which informs you
when the switch is using more than the configured percentage of PoE power.
For example, if the threshold is set at 50%, the switch informs you that it has
exceeded the threshold when 51% of available PoE power is being used. See
page 10-13 for an example. For more information on the threshold command,
see the Management and Configuration Guide on the ProCurve Web site at
www.hp.com/go/procurve/manuals. (See
page 1-15 for details.)
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