I read that active POE is safe, and that when performing the handshaking it can increase the voltage up to 10.1V. So I infer that generally Ethernet devices can handle 10V no problem. But what about 24V?
If one connects 24V passive PoE (pin 1&4 to +24V, pin 7&8 to gnd) to a non-PoE device, like a laptop, I have read that it could be damaged. As far as I understand ethernet is an isolated system, that use transformer couplings. If you put a DC voltage on the transformer nothing should happen.
How could a non POE device be damaged by a passive 24V POE device?