HP ProCurve zl Series Planning And Implementation Manual page 23

Planning and Implementation for the Series 3500yl Switches
Planning Your PoE Configuration
For example, the switch starts with 398 watts. Then it reserves 22 watts per
bank leaving 354 watts total for allocation. If ports 1-24 are chosen to be used
then the 22 watts that was held in reserve for that bank of ports will be added
back in for a total of 376 watts.
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 25-48, giving
a total number of powered ports of 25.
Another example would be to load balance or split the number of devices and
wattage between the two banks of ports. In this example the total wattage of
398 would be divided in half, 199 watts would be allocated to ports 1-24, and
199 watts would be allocated to ports 25-48.
By load balancing in this manner there could be 12 devices on one bank of
ports, say 1-24, and 13 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.
There is a CLI command available, the THRESHOLD command. It has an
informational only result. This command sets a threshold, by percent, to
inform you the switch is now using more than a certain percentage of PoE
power. For example if the threshold is set at 50%, the switch will issue an
information message informing you the switch has exceeded the threshold
when 51% of available PoE power is being used. Also see page 4-8 for an
example. For more information on the threshold command, Refer to the
Management and Configuration Guide which is on the ProCurve Web site,
www.procurve.com. (See page 1-4 for details.)
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