Power Over Ethernet (PoE) Operation
Planning and Implementing a PoE Configuration
Calculating the Maximum Load for a PoE Module
The maximum power available for a PoE module depends on the type of power
supplies used. ProCurve recommends that if you use more than one power
supply, use the same type of power supplies in your PoE implementation, that
is, two J8712A power supplies supplying 273 watts each for a total of 546 watts
of PoE power, or two J8713A power supplies supplying 900 watts of PoE
power each for a total of 1800 watts of PoE power.
When you connect the first PD to a PoE port, the PoE module must have a
minimum of 17 watts of PoE power available in order to detect and supply
power to the device. Each PoE module is allocated a minimum of 22 watts of
PoE power—17 watts for detection and additional 5 watts for variations in
any applied power loads. Depending on the amount of power the power supply
device delivers to a specific PoE module, there may or may not always be
enough power available to connect and support PoE operation on all 24 Gig-T
ports in a PoE module. PoE power is “available” if it is either not currently in
use or can be acquired by (automatically) removing PoE power from another,
lower-priority port.
After an appliance is connected to a PoE port, the switch reduces the power
requirement for that port from the initial 17 watts to the actual power level
the appliance requires.
Thus, after you have connected all but the last planned appliance to a PoE
module, there must be a minimum of 17 watts of unused PoE power available
on the module to support adding the final appliance. If you are using one
J8712A power supply powering one PoE module only (all 273 watts are
available to that module), the power is calculated as follows:
n= the total number of appliances you want to connect to one PoE module
and
w = the total PoE power required to operate (n - 1) appliances
then, the following must be true:
w + 17 ≤273
or
(273 – 17) ≥ w
11-25
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