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

12-10
Planning and Implementation for the HP 3800-PoE+ Switches
Planning the PoE+ Configuration
It takes 720 watts to fully provision 24 ports (plus 5 watts to account for load
fluctuations, 725 watts), therefore, at 110 voltage and 493 W, only 16 ports can
be provisioned. If a second power supply is added at 110 voltage, that would
add 700 watts because the 127 watts for system power would be coming from
the initial power supply. This would allow for a maximum of 1080 W for PoE/
PoE+ provisioning. This would allow for 36 ports to receive up to 30 W of PoE/
PoE+ power.
However, if the switch is supplied with 220 volts then there would be 815 W
for PoE/PoE+ provisioning. This would provision 27 ports with 30W of PoE+
power. If a second power supply is added at 220 volts, that would add 1000
watts because the 185 watts for system power would be coming from the initial
power supply. This would allow for a maximum of 1080 W for PoE/PoE+
provisioning. This would allow for 36 ports to receive up to 30 W of power.
These examples hold true unless the second power supply is configured as a
redundant power supply. Then all wattages must be figured on a single power
supply.
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
would be divided in half where half of the available watts would be allocated
to ports 1-24, and the other half would be allocated to ports 25-48.
By load balancing in this manner there could be a specified number of devices
on one bank of ports, say 1-24, and another specified number of devices on
the other bank of ports, 25-48 powered at an average of 30 watts each.
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. For more information on the
threshold command, Refer to the Management and Configuration Guide for
your switch at www.hp.com/networking/support.