Quick Introduction of PoE (Power over Ethernet)

Zyxel_LuciousZyxel_Lucious Zyxel Official Agent Posts: 208  mod
edited April 17, 2020 1:51PM in PoE
PoE Mode

The power management mode used by the Switch, whether it is in Classification or Consumption mode.

  • Classification - Select this if you want the Switch to reserve the maximum power for each PD according to the PD’s power class and priority level. If the total power supply runs out, PDs with lower priority do not get power to function. In this mode, the maximum power is reserved based on what you configure in Max Power or the standard power limit for each class.
  • Consumption - Select this if you want the Switch to supply the actual power that the PD needs. The Switch also allocates power based on a port’s Max Power and the PD’s power class and priority level. The Switch puts a limit on the maximum amount of power the PD can request and use. In this mode, the default maximum power that can be delivered to the PD is 33 W (IEEE 802.3at Class 4) or 22 W (IEEE 802.3af Classes 0 to 3).

PD Priority


When the total power requested by the PDs exceeds the total PoE power budget on the switch, you can set the PD priority to allow the switch to provide power to ports with higher priority first.


  • Critical has the highest priority.
  • High has the switch assign power to the port after all critical ports are served.
  • Low has the switch assign power to the port after all critical and high priority ports are served.

Power-Up Mode

The PoE standard that the switch uses to provide power to the port.

  • 802.3af - the Switch follows the IEEE 802.3af Power over Ethernet standard to supply power to the connected PDs during power-up.
  • Legacy - the Switch can provide power to the connected PDs that require high inrush currents at power-up. Inrush current is the maximum, instantaneous input current drawn by the PD when first turned on.
  • Pre-802.3at - the Switch initially offers power on the port according to the IEEE 802.3af standard, and then switches to support the IEEE 802.3at standard within 75 milliseconds after a PD is connected to the port. Select this option if the Switch is performing 2-event Layer-1 classification (PoE+ hardware classification) or the connected PD is NOT performing Layer 2 power classification using Link Layer Discovery Protocol (LLDP).
  • 802.3at - the Switch supports the IEEE 802.3at High Power over Ethernet standard and can supply power of up to 30W per Ethernet port. IEEE 802.3at is also known as PoE+ or PoE Plus. An IEEE 802.3at compatible device is referred to as Type 2. Power Class 4 (High Power) can only be used by Type 2 devices. If the connected PD requires a Class 4 current when it is turned on, it will be powered up in this mode.

Total/Current Power Consumption

In PoE Status, you can see the total power the Switch can provide to the connected PoE-enabled devices on the PoE ports, and the amount of power the Switch is currently supplying to the connected PoE-enabled devices.

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