We are configuring a UC540 and it looks like the 8th LAN port will not work. We have 7 phones connected and working, when we connect the 8th phone it does not work. We have swapped cables and phones and ports but this is not the issue. The 8th connected phone will not work, is this due to a limitation of the UC540?
The PoE capacity of a UC520 or UC540 is 88W. If you are using color screen 7900 series phones with the UC540, you might not have enough PoE capacity to power all 8 of your phones. You will probably need to use a power cube on one of your phones, or connect your extra phones to a separate PoE switch.
You can find out the PoE usage by using the show power inline command. Here is sample output from that command: