Managing Power-over-Ethernet Devices
PoE on the Switch
Cisco Small Business 200 Series Smart Switch Administration Guide 151
11
You can decide the following:
• Maximum power a PSE is allowed to supply to a PD
• During device operation, to change the mode from Class Power Limit to
Port Limit and vice versa. The power values per port that were configured
for the Port Limit mode are retained.
• Maximum port limit allowed as a per-port numerical limit in mW (Port Limit
mode).
• To generate a trap when a PD tries to consume too much and at what
percent of the maximum power this trap is generated.
The PoE-specific hardware automatically detects the PD class and its power limit
according to the class of the device connected to each specific port (Class Limit
mode).
If at any time during the connectivity an attached PD requires more power from the
switch than the configured allocation allows (no matter if the switch is in Class
Limit or Port Limit mode), the switch does the following:
• Maintains the up/down status of the PoE port link
• Turns off power delivery to the PoE port
• Logs the reason for turning off power
• Generates a trap to a remote log server
CAUTION Consider the following when connecting switches capable of supplying PoE:
The PoE models of the Sx200, Sx300, and Sx500 series switches are PSE (Power
Sourcing Equipment) that are capable of supplying DC power to attaching PD
(Powered Devices). These devices include VoIP phones, IP cameras, and wireless
access points. The PoE switches can detect and supply power to pre-standard
legacy PoE Powered Devices. Due to the support of legacy PoE, it is possible that
a PoE switch acting as a PSE may mistakenly detect and supply power to an
attaching PSE, including other PoE switches, as a legacy PD.
Even though Sx200/300/500 PoE switches are PSE, and as such should be
powered by AC, they could be powered up as a legacy PD by another PSE due to
false detection. When this happens, the PoE switch may not operate properly and
may not be able to properly supply power to its attaching PDs.
To prevent false detection, you should disable PoE on the ports on the PoE switches
that are used to connect to PSEs. You should also first power up a PSE device
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