Chapter 1: Overview
29
Powered Device
Classes Powered devices are grouped into the five classes listed in Table 2. The
classes are based on the amount of power the devices require. The
switches support all five classes.
Power Budget The AT-9000/12POE switch has a power budget of 125 watts. The
AT-9000/28POE switch has a power budget of 370 watts. These are the
maximum amounts of power the switches can provide at one time to the
powered devices.
The AT-9000/28POE switch has two power supplies. Each power supply
is responsible for providing 185 watts, or half, of the power budget. Both
power supplies must be connected to AC power sources for the switch to
provide the full 370 watts. The power budget is reduced to 185 watts if only
one power supply is connected to a power source.
The power requirements of the PoE devices determine the maximum
number of devices the switch can support at one time. So long as the total
power requirements of the powered devices is less than the power budget
of the switch, the switch can supply power to all of the devices. If the total
power requirements exceed the power budget, the switch denies power to
one or more ports using port prioritization.
To determine whether the power requirements of the PoE devices you
plan to connect to the switch exceed its power budget, refer to the devices’
documentation for their power requirements and add the requirements
together. The switch should be able to power all of the devices
simultaneously as long as the total is below its power budget. If the total
exceeds the available power budget, consider reducing the number of PoE
devices so that all of the devices receive power. Otherwise, the switch
powers a subset of the devices, based on port prioritization.
Table 2. IEEE Powered Device Classes
Class Maximum Power Output
from a Switch Port PD Power Range
0 15.4W 0.44W to 12.95W
1 4.0W 0.44W to 3.84W
2 7.0W 3.84W to 6.49W
3 15.4W 6.49W to 12.95W
4 30.0W 12.95W to 25.5W