OK so I've been reviewing a design for another engineering team, and they have taken the standard app notes for a ethernet interface...RJ45 to magnetics and then PHY.  Per the app's notes, they tie a cap from some of the interface lines to earth ground..least the symbol.  OK so this device is going to sit on the end of a ethernet cable, using PoE, so there is not ever a connection to a earth reference, unless its the shield of the cable but now we start to worry about ground loops.
   
  My thoughts are to just ground those caps to the main digital ground plane...or...make a seperate plane that sits under the connectors, etc and tie it back to the digital plane with a single point....ferrte bead, shunt...or leave open...gives the options at least.
   
  Any other thoughts?

       
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