Ken, It is a potential shock hazard if the coax run is long and runs from building to building (for instance) where the ground potentials may be different in the different buildings. One can develop a large potential on the shield of the cable, so that if you put yourself between the cable shield and ground you may get a strong shock. That is the reason for isolating the shield from more than one direct connection to ground. It is a real issue. The result for EMI is, as you have noted, the creation of an egregious EMI offender. I have used the chassis mounted BNC connectors with built-in capacitors successfully.
Jim Jim Knighten, Ph.D. Teradata, a Division of NCR http://www.ncr.com 17095 Via Del Campo San Diego, CA 92127 USA Tel: 858-485-2537 Fax: 858-485-3788 [email protected] -----Original Message----- From: Ken Javor [mailto:[email protected]] Sent: Wednesday, March 05, 2003 12:58 PM To: Knighten, Jim L; [email protected] Subject: Re: Ethernet coax connection Assume complete ignorance on my part. What is the safety concern? on 3/5/03 3:50 PM, Knighten, Jim L at [email protected] wrote: > Ken, > > Safety considerations are the reason for the spec requirement. You are > allowed to ground the shield at one point. > > Try using a BNC coax connector with a built-in capacitor to ground. That > gives you an AC connection to ground and is often quite effective. These > are off-the-shelf parts. > > Jim > > > Jim Knighten, Ph.D. > Teradata, a Division of NCR http://www.ncr.com > 17095 Via Del Campo > San Diego, CA 92127 > USA > Tel: 858-485-2537 > Fax: 858-485-3788 > [email protected] > > -----Original Message----- > From: Ken Javor [mailto:[email protected]] > Sent: Wednesday, March 05, 2003 12:38 PM > To: [email protected] > Subject: Ethernet coax connection > > > Question for list members: > > Background: I am troubleshooting a complex integration of military hardware > and COTS. One COTS piece of equipment has an RG-58 coaxial connection, but > the coax connector is an isolated feedthrough bnc. From a radiated > emissions point-of-view, that is hurting us. One of the engineers here said > that is part of the spec - Ethernet shields are not supposed to be chassis > grounded. > > Question: Can someone please explain the reason for that, and how this is > usually handled to minimize radiated emissions? > > Thank you. > > Ken Javor > EMC Compliance > Huntsville, Alabama > 256/650-5261 > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > -- Ken Javor EMC Compliance Huntsville, Alabama 256/650-5261 This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
