Allied Telesis AT-FS970M/16F8-LC, Installation Manual, Page: 40 / 106

Overview
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Note
PoE+ Class 4 powered devices (IEEE 802.3at) with a power range
of 12.95 to 25.5 watts must use LLDP to identify their power
requirements to the switch. Non-compliant PoE+ powered devices
that do not support LLDP will be limited to 802.3af (15.4 watts)
power levels.
Power Budget
The AT-FS970M/8PS, AT-FS970M/8PS-E and AT-FS970M/24LPS
Switches have a power budget of 185 watts. The AT-FS970M/24PS and
AT-FS970M/48PS Switches have 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-FS970M/24PS and AT-FS970M/48PS Switches have 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 a mechanism referred to as 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 their
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, you should consider reducing the
number of PoE devices so that all of the devices receive power.
Table 10. 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