PoE/PoE+ Planning and Implementation Guide 2011-09

2-6
Operating Rules
PoE Power Characteristics
For example if the threshold is set at 50%, the switch informs you that the
switch has exceeded the threshold when 51% of available PoE power is being
used.
For more information, see the Management and Configuration Guide for
your switch at:
www.hp.com/networking/support
PoE Power Characteristics
Line Loss
A certain amount of power is consumed by the resistance of the wire in the
LAN cable connected from the switch to the powered device (typically less
than 16% loss), which can be influenced by cable length, quality, and other
factors. The IEEE 802.3af specification has addressed loss of power by
providing more power than a powered device requires. As well, depending
upon the classification (Class 0-4) of the device, the switch will provide more
or less power to address the specific power needs of that end device.
PD Power Classification
A PD is classified based on the maximum power it draws across all input
voltages and operational modes. The most common class is 0, in which the
switch will allow a maximum draw of 15.4 watts per port. As an example, 15.4
watts - Power Loss (16%) = 12.95 watts. See Table 2-1.
Table 2-1. Power Usage
Class Usage Minimum Power Levels
at Output of PSE
Range of Maximum
Power required by
the PD
0 Default 15.4 watts 0.44 to 12.95 watts
1 Optional 4.0 watts 0.44 to 3.84 watts
2 Optional 7.0 watts 3.84 to 6.49 watts
3 Optional 15.4 watts 6.49 to 12.95 watts
4 Optional 30 watts 0.05 to 24.00 watts