When plugging in a certain number of PoE devices (PDs) into a Zyxel PoE switch, it could be that only a certain number of PDs will boot up. It is because of the PoE switch has a fixed allocated capacity to provide PoE power (please refer to the device datasheet for their allocated capacity detail of PoE). So if the total usage of PDs is reaching the allocated capacity of the switch, the lower priority PD will not get power from the switch. Under this restriction, you still would enlarge the connecting PDs amount as much as possible by changing the PoE mode of a switch.
On the PoE switch, there are two different PoE Modes available:
The max power(mW) of the PD will be reserved for each PD according to the priority level for each port.
Power will be distributed so each device receives power. The power allocated by the switch may be less than the max power(mW) of the PD.
On factory default configuration, the PoE mode is set up to Classification.
When using Classification, the switch follows the standard defined to provide the PDs with max power. It is to guarantee that the PD could have enough power anytime. The allocated power will be reserved only for this PD's usage, no matter it needs the power or not at that moment.
However, the PD does not always require max power during the running status. So the use of Consumption mode would let the switch allocate the power more effectively. With the Consumption mode, the switch will try to let every connecting PD get power, and only provide the power according to the PD's request. So it could power on more PDs as it could with Classification.
Please note, that if the switch is facing a low PoE power situation, no matter which modes you use, the switch will base on the priority of PoE setting for each port to provide PD power.
If you are using a GS2210-8HP or a similar switch and only use a few ports to provide PoE and your connected PDs will not start as expected please try these steps:
1. Log into the switch by using it's local IP address and credentials.
2. Navigate to the Basic Setting > PoE Setup.
3. The PoE-Mode is set to Classification by default. Change this to Consumption mode and apply/save this configuration.
4. Reconnect those PDs to the switch.