User Manual

Manage Power over Ethernet
365
Insight Managed 28-Port and 52-Port Gigabit Ethernet Smart Cloud Switches
The following table shows the device classes for PoE+ devices adhering to the IEEE 802.3at
standard. The device classes for PoE devices adhering to the IEEE 802.3af standard are
identical with the exception that Device Class 4 is not supported.
Power Allocation and Power Budget
The switch is a smart switch in that it can allocate the required power to a connected device
by using a prioritization scheme: By default, power is supplied in ascending port order (that
is, lower port numbers are served first) until the power budget is consumed and insufficient
power remains to allocate to the next device. When less than 7W of PoE power is available
on a port, the port PoE LED lights yellow, and the attached device does not receive power
from the port. However, the switch continues to send data through the port connection.
You can manually change the prioritization scheme by changing the port priority (see Manage
and View the PoE+ Port Configuration on page 368).
The switch is also a smart switch in that it can override the IEEE power classification of a
powered device (PD): If the PD consumes less power than required by its power
classification, the switch provides only the power that the PD consumes instead of the power
that is required by the PD’s power classification.
If some PoE+ ports are in use and deliver power, you can calculate the available power
budget for the other PoE+ ports by subtracting the consumed (that is, delivered power) from
the total available power budget. (For information about the total available power budget, see
PoE Overview on page 364.)
An example:
Port 1 delivers 4.4W to a PD. The available power budget is 385.6W (390W–4.4W).
Another example:
A Class 4 PD is attached to Port 1, a Class 2 PD to Port 2, and another Class 4 PD to Port 3.
However, the PDs consume less power than defined by their classes: The PD attached to
Port 1 consumes 7.3W, the PD attached to Port 2 consumes 4.7W, and the PD attached to
Port 3 consumes 8.9W. So even though the switch provides power to two Class 4 devices
and one Class 3 device, the available power budget is 369.1W (390W–7.3–4.7–8.9W).
Table 84. PoE and PoE+ device class power allocation
Device
Class
Standard Range of Power
Delivered to the
Powered Device
Minimum Output at
PoE Switch Port
(Minimum Allocated)
Maximum Output at
PoE Switch Port
(Maximum Allocated)
0 PoE and PoE+ 0.44W–12.95W 15.4W 16.2W
1 PoE and PoE+ 0.44W–3.84W 4.0W 4.2W
2 PoE and PoE+ 3.84W–6.49W 7.0W 7.4W
3 PoE and PoE+ 6.49W–12.95W 15.4W 16.2W
4 PoE+ only 12.95W–25.5W 30.0W 31.6W