I have the 8851. I have tried two different models of expansion modules (one at a time), but they are either not being recognized or I am somehow not getting enough power to power up the phone. The two expansion modules that I have tried are the CP-8800-A-KEM and 8800-CP-BEKEM.
The product is CP-8851-3PCC.
The firmware is sip88xx.11-2-3MPP-398.loads.
I have logged into the IP address and believe that everything is configured correctly. I have attached a screenshot of the relevant settings.
If the warning is "not getting enough power to power up the phone" the port power is not sufficient enough to power the expansion module. you need to think of power cube in this case or connect it to POE+ port.
I have both the network cable and a power cube connected. I am assuming that it's only power source is the power cube and that the network cable is only there to provide the signal.
You know what they say about assumptions, right? Their the mother of all F-ups. Better to know then to speculate. Find out what and how you power the phone and then you'll likely have a much bigger chance to get better help with this.
Below mentioned is the power requirement to turn on the module.
If you power the phone with POE, you should check whether the switch has enough power for power up it or not. If you power it with powercube, be sure that it's compatible with power cube4.
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