I am examining the possibilities for building a cheap ethernet device that would be powered over ethernet using PoE technology. I came across this article which shows the generic block diagrams:
Looking around, I always find the DC-DC converters used in PoE applications to be isolated. I am trying to understand whether that is always necessary. Assuming that the PoE RJ45 cable would be the only cable connected to my device, is there really any reason for me to isolate from the input voltage? This is also assuming that the data lines are already isolated, so the only potentials without isolation is the power lines.
To clarify more: I still want the TX and RX lines to stay isolated via transformers. I just want to skip the DC-DC part isolation (just graetz bridge, bulk capacitor and a DC-DC converter without isolation.) I don't mind being not compliant with the standard here. As for the shielding, I would leave it disconnected.