Chas, The original post states the Ethernet is shielded. That was indeed the basis of my response.
Ken > From: "Grasso, Charles" <[email protected]> > Date: Wed, 7 Mar 2007 14:26:42 -0700 > To: "Ken Javor" <[email protected]>, <[email protected]> > Subject: RE: Ethernet connector shield decoupling capacitor > > Hi Ken. Is the assumption that the externally run Ethernet > is shielded? Then I can see how ground potentials can be > as issue. > > Typically all the internal stuff is unshielded. > > Best Regards > Charles Grasso > Compliance Engineer > Echostar Communications Corp. > Tel: 303-706-5467 > Fax: 303-799-6222 > Cell: 303-204-2974 > Pager/Short Message: [email protected] > Email: [email protected] > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of Ken > Javor > Sent: Wednesday, March 07, 2007 2:19 PM > To: [email protected] > Subject: Re: Ethernet connector shield decoupling capacitor > > I think there are others on this forum who understand this better than I > do; > in fact I learned this from someone else on this forum. Ethernet can > run a > long way, and if it connects two pieces of equipment whose enclosures > are at > slightly different mains frequency potentials, due to their green wires > going to different grounds, that can cause current to flow through an > Ethernet shield grounded at both ends. Hence the capacitive decoupling > which is a high impedance at the mains frequency. This answer assumes > that > your digital ground is tied to chassis ground, which I believe is > typical. > >> From: "Jim Eichner" <[email protected]> >> Date: Wed, 7 Mar 2007 12:05:08 -0800 >> To: <[email protected]> >> Subject: Ethernet connector shield decoupling capacitor >> >> We're being hit with a requirement that I don't understand. >> >> We are using a shielded Ethernet connector that contains the typical > 2kV >> cap from the common point of the 75 ohm resistors to the shield. This >> is used on the output of an off-the-shelf Ethernet transceiver module, >> and the mfr of that module is telling us we need to connect the >> connector shield to their digital ground through a 1nF 250V Y-cap, not >> directly. >> >> 1. Why not directly connect the shield to digital ground? >> >> 2. Why would a Y-cap be required? The cap would be joining two parts > of >> the same circuit, so it would not be across an isolation boundary. I >> can't think of a reason to require either the 250V rating or the Y >> rating. >> >> Any thoughts anyone? >> >> Thanks, >> >> Jim Eichner, P.Eng. >> Manager - Compliance Engineering >> Xantrex Technology Inc. >> e-mail: [email protected] >> web: www.xantrex.com >> >> Confidentiality Notice: This email message, including any attachments, >> is for the sole use of the intended recipient(s) and may contain >> confidential and privileged information. Any unauthorized review, use, >> disclosure or distribution is prohibited. If you are not the intended >> recipient, please contact the sender by reply e-mail and destroy all >> copies of the original message. >> >> - >> ---------------------------------------------------------------- >> This message is from the IEEE Product Safety Engineering Society >> emc-pstc discussion list. Website: http://www.ieee-pses.org/ >> >> To post a message to the list, send your e-mail to [email protected] >> >> Instructions: http://listserv.ieee.org/request/user-guide.html >> >> List rules: http://www.ieee-pses.org/listrules.html >> >> For help, send mail to the list administrators: >> >> Scott Douglas [email protected] >> Mike Cantwell [email protected] >> >> For policy questions, send mail to: >> >> Jim Bacher: [email protected] >> David Heald: [email protected] >> >> All emc-pstc postings are archived and searchable on the web at: >> >> http://www.ieeecommunities.org/emc-pstc > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Jim Bacher: [email protected] > David Heald: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
