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Rockwell Automation Publication 1783-UM007I-EN-P - December 2017 233
Configure Switch Features Chapter 3
Configuration options include the following:
•
Limit the total power supported.
•
Configure mode and power settings for individual ports.
For most applications, the default configuration (Auto mode) is sufficient and
no further configuration is required. However, you can customize the settings
to meet your needs. For example, be sure that power is pre-allocated to a
specific port, set the port mode to Static. As another example, to disallow
high-power devices on a port, set the mode to Auto and specify a maximum
power limit.
Powered Device Detection and Initial Power Allocation
A switch or expansion module detects a powered device when a port with PoE
capability is active, PoE is enabled (the default), and the connected device is
not powered by another power source.
After device detection, the switch determines the device power requirements
that are based on its type:
•
The switch classifies the detected 802.3 af/at compliant IEEE device
within a power consumption class. Based on the available power in the
power budget, the switch determines if a PoE port can be powered.
Table 90 lists these levels.
IMPORTANT When you make PoE configuration changes to a port, the port drops power.
Whether the port powers up again depends on the new configuration, the
state of the other PoE ports, and the state of the power budget.
For example, if port 1 is in Auto mode and the On state, and you configure it
for Static mode, the switch removes power from port 1, detects the powered
device, and repowers the port.
If port 1 is in Auto mode and the On state and you configure it with a
maximum wattage of 10 W, the switch removes power from the port and
then redetects the powered device. The switch repowers the port only if the
powered device is a Class 1, Class 2, or a Cisco-only powered device.
Table 90 - IEEE Power Classifications
Class Power Supplied per Port, Max
0 (class status unknown) 15.4 W
1 4 W
2 7 W
3 15.4 W
4 30 W PoE+ devices only