basic doubt in PoE tech...

[commworld]

hello,
I am studying about Power over Ethernet.
Can anybody please explain as why the ethernet cables are transformer coupled at each ends??
The POE configuration is shown in the image below..

 

[kkwd]

The image you provide is Mid Span mode.The 48V DC power supply via the unoccupied twisted-pair.
The other mode is End Span. The 48V DC power supply via centre tapped transformer.

 

[FoxyRick]

The data-carrying cables are transformer coupled to provide isolation between the equipment; they might be on different ground levels so cannot simply be connected together. That is normal and nothing to do with the PoE capability.