Cisco Small Business 200 Series Administration Manual page 174

Port Management: PoE
PoE on the Device
The following can be configured:
• 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.
Changing the mode from Class Limit to Port limit and vice versa when the device is operational
NOTE
forces the PD to reboot.
• 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 device than the
configured allocation allows (no matter if the device is in Class Limit or Port Limit mode), the device 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 an SNMP trap
!
CAUTION
Cisco Small Business 200 Series Smart Switch Administration Guide
Consider the following when connecting switches capable of supplying PoE:
The PoE models of the Sx200, Sx300, and SF500 series switches are PSE capable
of supplying DC power to attaching PDs. These devices include VoIP phones, IP
cameras, and wireless access points. The PoE switches can detect and supply
power to pre-standard legacy PoE PDs. Due to the support of legacy PoE, it is
possible that a PoE device 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 device 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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