I'm interested to know how you expect a ground loop to form with a unit that has no ground. ;-) Assuming, that is, that it's correctly isolated (1.5kV) from the ethernet wires, and even if it's not the other end will be (though a long antenna still gathers a charge) Grounding that particular cap depends largely on the environment. Much of the reason for that cap is to reduce EMI traveling from your device into the ethernet wire through various couplings (capacitive, inductive), as well as provide a ground reference to the cable that's not going to allow a DC ground loop. I've always connected it as close to the power supply ground as possible with a thick trace and a 0603 0 ohm resistor, with the idea that an inductor or ferrite can replace the resistor if a problem is found later, or for specific installations. Have never needed to use it, though... -Adam On Dec 5, 2007 1:50 PM, alan smith wrote: > 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? > > > --------------------------------- > Never miss a thing. Make Yahoo your homepage. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Moving in southeast Michigan? Buy my house: http://ubasics.com/house/ Interested in electronics? Check out the projects at http://ubasics.com Building your own house? Check out http://ubasics.com/home/ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist