after getting the center tap pins for poe, I have an example schematic to design an EARTH ground. I have the understanding that that would be our Earth in AC over cabinet. That would remove our value for doing this entire poe design, as we only want the ethernet line coming into the design. How can I provide "Earth" in this case. Can I just share it with ground on the pcb? The reality is that our design will utilize a pse with poe+ type B, but that isn't the scope of our PD. We want this to be 802.3 at compliant. So we must rectify, regardless if our pse is DC constant. With that in mind, what engineering technique should I follow to provide ground/ Earth in this image?
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That's not "Earth" literally, but it could be. It depends on your exact scenario, but if your RJ45 socket has a metal shell, it connects to that, as it might be Earth if you are using an STP cable whose shielding connects the metal shells of connectors together.
If you have a metal enclosure, the RJ45 metal shell should in general connect to the metal enclosure.
For example a generic desktop PC will have RJ45 metal shell connected to metal chassis, and the metal chassis connects to PE via mains plug, so it will be earthed.
And that's what you need to do whether or not your design uses PoE. These are unrelated.
If you are doing a PD, it depends if it must be isolated or not. If there are no other connections then the innards can be non-isolated, but if there is a possibility for someone to connect something so that the PD cannot be non-isolated, then you need an isolated PoE converter.
