The Power Over Ethernet spec requires isolation at both ends of the line. Ok, we've lifted some of the POE concepts for a non-Ethernet application and all is fine. I'm looking to expand the system and isolation is getting to be a pain in the neck.
Basically, we're driving from RS-422 drivers, through CAT-5, transformer coupled at both ends. Like POE, we're supplying power via the center taps of the TxD and RxD pairs. However, we also have a couple of sideband '422 signals with isolated drivers and receivers at each end. Is isolation really needed at both ends? I'm trying to see a failure mode where lack of isolation causes grief (remember, power always comes from one end - the other is a slave). That's one case.
In another case, we want to drive several of these POE isolated "slaves" from the same widget. Is isolation on the driving end required? They're isolated at the load, so the local ground *shouldn't* matter.
If I remove the isolation in the powered end, what safety do I give up? Where is the dangerous fault? I'm not seeing why POE requires isolation at both ends, other than Ethernet does.