Calculating The Maximum Load For An Xl Poe Module - HP ProCurve 6400cl Series Management And Configuration Manual

Power Over Ethernet (PoE) Operation for the Series 5300xl Switches

Calculating the Maximum Load for an xl PoE Module

Since the full PoE load on an xl PoE module receiving 408 watts (from an EPS
supporting only that module) cannot exceed 369.6 watts (24 ports with a
maximum of 15.4 watts per port), there is no concern for overloading the
module's PoE capacity. However, for xl PoE modules receiving 204 watts due
to EPS power-sharing with another PoE device, it is possible to exceed the
maximum supportable load. Also, when planning the PoE load, the following
factors apply per-module:
■ When first connecting an appliance to a PoE port, the xl PoE module
must have a minimum of 15.4 watts of available PoE power. 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 on the module. (See to "PD Support" on page 11-6.)
After an appliance is connected to a PoE port, the switch reduces the
■
power requirement for that port from the initial 15.4 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 15.4 watts of unused PoE power available
on the module to support adding the final appliance. That is, where:
n
= the total number of appliances you want to connect to one xl PoE
module
and
w
= the total PoE power required to operate (
then, the following must be true:
or
For example, suppose you have 24 identical appliances to connect to an xl
PoE module receiving 204 watts of PoE power. For this example, each
appliance requires 8.3 watts to operate. In this case, the module would support
only 23 of these appliances at any given time because there would not be
enough unused power to meet the minimum of 15.4 watts required to support
the initial bring-up of the 24th appliance. That is, 204 - (23 x 8.3) = 13.1. Because
the module provisions power on the basis of the priority scheme described on
page 11-10 (under the interface < port-list > power [ critical | high | low ] syntax),
Planning and Implementing a PoE Configuration
n
w
+ 15.4 ≤ 204
w
(204 – 15.4) ≥
- 1) appliances
11-21