Hi!
I have Lite5 device on my roof and FTP cable ~40 meters far. When I plug-in power, I'm able to connect to Lite5 only with 10mbit/s speed. I cut ~5 meters and trying again. No luck. In 100 mbit/s mode, my connection breaks every sec (connect-disconnect..).
So..35 meters and no 100mbits over PoE with standard adapter?:O

try another cable. Or another POE injecotr

Cutted cable.. ;( Didn't found passive PoE injectors for my AP. Only 802.11af which are active ones.

Have you tested your cable? If not you are using a 24V PoE power injector, correct? When it is connected and communicating at the 10Mbps speed you can go to System -> Health and it will show you your voltage. Anything above 20V is "OK" in my opinion. 40m is well withing the range of a STP cable. Did you mean to say STP cable instead of FTP?

If I'm not mistaken, Health shows nothing for me (ROS 6.5).
And nope, by FTP I meant FTP - foiled twisted pair, not STP (shielded twisted pair)