11-23
Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 11 Configuring Interface Characteristics
Configuring Ethernet Interfaces
Budgeting Power for Devices Connected to a PoE Port
When Cisco powered devices are connected to PoE ports, the switch uses Cisco Discovery Protocol
(CDP) to determine the actual power consumption of the devices, and the switch adjusts the power
budget accordingly. This does not apply to IEEE third-party powered devices. For these devices, when
the switch grants a power request, the switch adjusts the power budget according to the powered-device
IEEE classification. If the powered device is a Class 0 (class status unknown) or a Class 3, the switch
budgets 15,400 milliwatts for the device, regardless of the actual amount of power needed. If the
powered device reports a higher class than its actual consumption or does not support power
classification (defaults to Class 0), the switch can power fewer devices because it uses the IEEE class
information to track the global power budget.
By using the power inline consumption wattage configuration command, you can override the default
power requirement specified by the IEEE classification. The difference between what is mandated by the
IEEE classification and what is actually needed by the device is reclaimed into the global power budget
for use by additional devices. You can then extend the switch power budget and use it more effectively.
For example, if the switch budgets 15,400 milliwatts on each PoE port, you can connect only 24 Class 0
powered devices. If your Class 0 device power requirement is actually 5000 milliwatts, you can set the
consumption wattage to 5000 milliwatts and connect up to 48 devices. The total PoE output power
available on a 24-port or 48-port switch is 370,000 milliwatts.
Caution You should carefully plan your switch power budget and make certain not to oversubscribe the power
supply.
Note When you manually configure the power budget, you must also consider the power loss over the cable
between the switch and the powered device.
When you enter the power inline consumption default wattage or the no power inline consumption
default command, this caution message appears:
%CAUTION: Interface interface-id: Misconfiguring the 'power inline consumption/allocation'
command may cause damage to the switch and void your warranty. Take precaution not to
oversubscribe the power supply. Refer to documentation.
For more information about the IEEE power classifications, see the “Power over Ethernet Ports” section
on page 11-6.
Beginning in privileged EXEC mode, follow these steps to configure the amount of power budgeted to a
powered device connected to each PoE port on a switch:
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
no cdp run (Optional) Disable CDP.
Step 3
power inline consumption default
wattage
Configure the power consumption of powered devices connected to each
the PoE port on the switch. The range for each device is 4000 to
15400 milliwatts. The default is 15400 milliwatts.
Step 4
end Return to privileged EXEC mode.
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