Re: Ethernet coax connection
Hi Group, I watched this interesting thread and noticed that none of you recalled the susceptibility of the system. We had severe problems with susceptibility of computers with Ethernet coax connection. As a matter of fact did not find any computer meeting the requirements for industrial environment of the 61000-4-4 (burst). They all failed at levels of a couple of hundred volts. Using capacitor coupled BNCs helps a bit. We simply bonded the shield to ground. I have to notice, that all computers attached to the network were in the same floor of the same building. Best regards George ** * Dr. Georg M. Dancau * HAUNI MASCHINENBAU AG * * g.m.dan...@ieee.org * Manager Product Development* * TEL: +49 40 7250 2102 * K.A.Koerber Chaussee 8..32 * * FAX: +49 40 7250 3801 * 21033 Hamburg, Germany * ** * home: Tel: +49 4122 99453 * Hauptstr. 60a * * Fax: +49 4122 99454 * 25492 Heist, Germany * * Cellular: +49 175 5805280** ** From: Ken Javor ken.ja...@emccompliance.com To: Stone, Richard A (Richard) rsto...@lucent.com; 'Knighten, Jim L' jk100...@teradata-ncr.com; emc-p...@majordomo.ieee.org Sent: Wednesday, March 05, 2003 11:10 PM Subject: Re: Ethernet coax connection Thanks to all who answered in MINUTES assisting an EMI troubleshoot on something that is of great national value. This forum is a tremendous resource! on 3/5/03 4:46 PM, Stone, Richard A (Richard) at rsto...@lucent.com wrote: we've had good success with the built capacitance of 9000pf as well, depending on test being discussed and frequency, certain cap. values from the shielded ring of the UNgrounded ring to earth works well for low freq.. 30 mhz. Richard, -Original Message- From: Knighten, Jim L [mailto:jk100...@teradata-ncr.com] Sent: Wednesday, March 05, 2003 4:12 PM To: Ken Javor; emc-p...@majordomo.ieee.org Subject: RE: Ethernet coax connection 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:58 PM To: Knighten, Jim L; emc-p...@majordomo.ieee.org 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 jk100...@teradata-ncr.com 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:38 PM To: emc-p...@majordomo.ieee.org 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
RE: Ethernet coax connection
George, The physics of this is quite understandable. If you have a piece of electronic gear that emits radiation, it will also receive radiation with similar efficiency. If you provide the AC short to chassis ground that the BNC capacitor provides, then not only is internal radiation shunted to chassis and prevented from getting outside the chassis, but external radiation is also shunted to chassis which makes it more difficult for it to penetrate into the sensitive internal regions of the electronic system. Bonding all the shields to ground is an eminently practical solution, but you produce a custom system, as another poster noted, rather than a 10Base2 system. 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 jim.knigh...@ncr.com -Original Message- From: Georg M. Dancau [mailto:g.m.dan...@dancau.de] Sent: Sunday, March 09, 2003 1:16 PM To: Ken Javor; emc-p...@majordomo.ieee.org Subject:Re: Ethernet coax connection Hi Group, I watched this interesting thread and noticed that none of you recalled the susceptibility of the system. We had severe problems with susceptibility of computers with Ethernet coax connection. As a matter of fact did not find any computer meeting the requirements for industrial environment of the 61000-4-4 (burst). They all failed at levels of a couple of hundred volts. Using capacitor coupled BNCs helps a bit. We simply bonded the shield to ground. I have to notice, that all computers attached to the network were in the same floor of the same building. Best regards George ** * Dr. Georg M. Dancau * HAUNI MASCHINENBAU AG * * g.m.dan...@ieee.org * Manager Product Development* * TEL: +49 40 7250 2102 * K.A.Koerber Chaussee 8..32 * * FAX: +49 40 7250 3801 * 21033 Hamburg, Germany * ** * home: Tel: +49 4122 99453 * Hauptstr. 60a * * Fax: +49 4122 99454 * 25492 Heist, Germany * * Cellular: +49 175 5805280** ** From: Ken Javor ken.ja...@emccompliance.com To: Stone, Richard A (Richard) rsto...@lucent.com; 'Knighten, Jim L' jk100...@teradata-ncr.com; emc-p...@majordomo.ieee.org Sent: Wednesday, March 05, 2003 11:10 PM Subject: Re: Ethernet coax connection Thanks to all who answered in MINUTES assisting an EMI troubleshoot on something that is of great national value. This forum is a tremendous resource! on 3/5/03 4:46 PM, Stone, Richard A (Richard) at rsto...@lucent.com wrote: we've had good success with the built capacitance of 9000pf as well, depending on test being discussed and frequency, certain cap. values from the shielded ring of the UNgrounded ring to earth works well for low freq.. 30 mhz. Richard, -Original Message- From: Knighten, Jim L [mailto:jk100...@teradata-ncr.com] Sent: Wednesday, March 05, 2003 4:12 PM To: Ken Javor; emc-p...@majordomo.ieee.org Subject: RE: Ethernet coax connection 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:58 PM To: Knighten, Jim L; emc-p...@majordomo.ieee.org 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 jk100...@teradata-ncr.com 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 jim.knigh...@ncr.com
RE: Ethernet coax connection
The one-point connection od the 10 Base- coax shield is specified by IEEE standard 802.3. In my (2000) revision, it is e.g. in paragraph 8.7.2.2., page 158. to prevent the building up of voltages that may result in undue hazard to connected equipment or to persons. However, when twisted-pair (differential) interface is used in 10/100/ and 1000 Mbps Ethernet, the cabling may be unshielded twisted pair (UTP) or shielded twisted pair (STP). There isn't such a requirement to connect the shield at only one side in that case. E.g. section 41.4.2.2 of the same standard describes it, and it says that if the shielded cable is used, then the shield may be grounded at both ends according to local regulations and ISO/IEC 11801, 1995, and as long as the ground potential difference between both ends of the network segments is less than 1 Vrms. Neven Rich, I think you must be correct. I do have anecdotal evidence of persons being knocked on their butts by grabbing hold of an Ethernet coax in a large facility and trying to connect it to a computer. My experience is in EMC and the 10Base2 Ethernet (coax) is a persistent offender. (Actually, the twisted pair stuff has its own set of EMC problems.) Regards, 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 jim.knigh...@ncr.com -Original Message- From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Wednesday, March 05, 2003 4:31 PM To: Knighten, Jim L Cc: ken.ja...@emccompliance.com; emc-p...@majordomo.ieee.org Subject: Re: Ethernet coax connection Hi Jim: 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. I don't believe the issue is that of electric shock. I don't believe the current and resistance of the neutral are high enough to develop 30 volts (the shock hazard limit). Instead, I believe the problem is that, with two connections, the shield is in parallel with the neutral. That means that some of the neutral current will pass through the shield, and will likely open a PWB trace somewhere. In the process, the PWB trace heating may start a fire. I believe the circuit is: (You may not be able to read this schematic if your mail reader is not set for plain ASCII text.) L Bldg A +-++ | || | || | | | | (~) 120 V | | | load | | | | | || |N|| +-++-+-+ |utility | || Bldg A | |ground | || ground | |rod | || rod |PE BNC shield - | | - ++ ---| | --- | - | |-| | | | | | | | | | | | L Bldg B | ++| ||| ||| | | | | | | | load | | | | | ||| | N || ++-+-+| | Bldg B | | | ground | | | rod |PE| - ++ --- BNC shield - You can see from the schematic that the shield is in parallel with both the neutral and the earth-ground. Being in parallel, it will carry some of the neutral current, depending on the respective resistances. Because of both the neutral and the earth-ground, the voltage should never approach 30 volts (1/4 of the mains voltage). But, there can be a very high current in the shield of the BNC cable
RE: Ethernet coax connection
I seem to recall that -years ago- IBM had an interface DC voltage spec. IBM required that BEFORE attaching a building-to-building interface cable to an EUT, that a DC voltage measurement be made between the shield of the cable and the EUT chassis. If the voltage exceeded 1.5V (I think) the installer was instructed NOT to attach the cable. If this problem has gone away - maybe to better building codes - the hurrah!. This was not always the case. Best Regards Charles Grasso Senior Compliance Engineer Echostar Communications Corp. Tel: 303-706-5467 Fax: 303-799-6222 Cell: 303-204-2974 Email: charles.gra...@echostar.com; Email Alternate: chasgra...@ieee.org From: Knighten, Jim L [mailto:jk100...@teradata-ncr.com] Sent: Thursday, March 06, 2003 10:17 AM To: john...@itesafety.com Cc: emc-p...@majordomo.ieee.org Subject: RE: Ethernet coax connection I knew that I was headed for trouble when I responded to Ken Javor original question about EMI frustrations with 10Base2 Ethernet. I figured the safety guys would pummel me a little - and I accept the comments. However, I couldn't resist since I have experienced the same EMI frustrations. Nevertheless, good EMI engineers are sometimes faced with an existing design that uses 10Base2 (legacy, if you will) and has the severe EMI problem that an experienced EMI engineer could anticipate. Ignoring it is unacceptable from a regulatory point of view (in the case of commercial products), or from other spec and/or contract reasons in the government world. Many, if not most of the practical solutions appear to violate either the letter or the spirit of the Ethernet 10Base2 spec. This puts the EMI engineer in the same seemingly untenable spot that Ken Javor appeared to be in yesterday. I've been there and I empathize. 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 jim.knigh...@ncr.com -Original Message- From: Robert Johnson [mailto:john...@itesafety.com] Sent: Wednesday, March 05, 2003 9:53 PM To: Knighten, Jim L Cc: emc-p...@majordomo.ieee.org Subject:RE: Ethernet coax connection File: Robert Johnson.vcf If you have shock level differences between the grounds in two different buildings, either an entire building isn't connected to an earth electrode, or someone is paying a whopping electric bill to heat up mother earth. I suspect the shock situation you were talking about was a power cross condition, either to the cable or within equipment. I hope it was diagnosed and fixed. The voltage differences between two buildings are generally very low, on the order of a couple volts, but due to fractional ohm impedances are capable of very high currents. Building maintenance procedures should routinely be checking for ground currents since they indicate faults in the power system. Note that in accordance with IEC 62102, 10base2 is an SELV circuit and should not be used for exposed plant (between building) wiring. Ethernet distance specs and application recommendations also go against exposed plant wiring. Ethernet 10base5 is considered a TNV-1 circuit and suitable for exposed plant use, is insulated and requires single point grounding. Optical fiber is a better recent development and the best answer for exposed plant lines these days. Note that IEC 62102 provides an extensive list of interconnect circuit types and what category they fit into with regard to shock level (SELV, TNV, hazardous, etc). It's an important reference for any engineer designing interconnect circuits in determining isolation needs. Bob Johnson ITE Safety From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of Knighten, Jim L Sent: Wednesday, March 05, 2003 7:51 PM To: Rich Nute Cc: ken.ja...@emccompliance.com; emc-p...@majordomo.ieee.org Subject: RE: Ethernet coax connection Rich, I think you must be correct. I do have anecdotal evidence of persons being knocked on their butts by grabbing hold of an Ethernet coax in a large facility and trying to connect it to a computer. My experience is in EMC and the 10Base2 Ethernet (coax) is a persistent offender. (Actually, the twisted pair stuff has its own set of EMC problems.) Regards, 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 jim.knigh...@ncr.com -Original Message- From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Wednesday, March 05, 2003 4:31 PM To: Knighten, Jim L Cc: ken.ja...@emccompliance.com; emc-p...@majordomo.ieee.org Subject:Re: Ethernet coax connection Hi Jim: 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
RE: Ethernet coax connection
ANSI/IEEE 802.3 specifies 10Base2 earthing at some point along the cable, but not at any node. 10Base2 nodes typically are an isolated (DC/DC + level shifter) 9-volt part of the PBWA with a high resistance connection to chassis. [RF radiation is higher and RF immunity is lower than 10BaseT. The 'shield' is a conductor so it radiates if not earthed.] To reduce emissions ground the cable at a single point (typical office installations had punch blocks in the wiring closet); additional points may introduce ground loops. Other replies suggest an AC ground...you need to eliminate odd-order harmonics (typically 5th to 13th). Also check COTS 10Base2 component specifications: some were only Class A. It is difficult dealing with legacy technology. Choices of COTS 10Base2 are limited, EMC modifications change it to 'custom.' David From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 3:38 PM To: emc-p...@majordomo.ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
Re: Ethernet coax connection
Thanks to all who answered in MINUTES assisting an EMI troubleshoot on something that is of great national value. This forum is a tremendous resource! on 3/5/03 4:46 PM, Stone, Richard A (Richard) at rsto...@lucent.com wrote: we've had good success with the built capacitance of 9000pf as well, depending on test being discussed and frequency, certain cap. values from the shielded ring of the UNgrounded ring to earth works well for low freq.. 30 mhz. Richard, -Original Message- From: Knighten, Jim L [mailto:jk100...@teradata-ncr.com] Sent: Wednesday, March 05, 2003 4:12 PM To: Ken Javor; emc-p...@majordomo.ieee.org Subject: RE: Ethernet coax connection 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:58 PM To: Knighten, Jim L; emc-p...@majordomo.ieee.org 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 jk100...@teradata-ncr.com 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:38 PM To: emc-p...@majordomo.ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
RE: Ethernet coax connection
I knew that I was headed for trouble when I responded to Ken Javor original question about EMI frustrations with 10Base2 Ethernet. I figured the safety guys would pummel me a little - and I accept the comments. However, I couldn't resist since I have experienced the same EMI frustrations. Nevertheless, good EMI engineers are sometimes faced with an existing design that uses 10Base2 (legacy, if you will) and has the severe EMI problem that an experienced EMI engineer could anticipate. Ignoring it is unacceptable from a regulatory point of view (in the case of commercial products), or from other spec and/or contract reasons in the government world. Many, if not most of the practical solutions appear to violate either the letter or the spirit of the Ethernet 10Base2 spec. This puts the EMI engineer in the same seemingly untenable spot that Ken Javor appeared to be in yesterday. I've been there and I empathize. 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 jim.knigh...@ncr.com -Original Message- From: Robert Johnson [mailto:john...@itesafety.com] Sent: Wednesday, March 05, 2003 9:53 PM To: Knighten, Jim L Cc: emc-p...@majordomo.ieee.org Subject:RE: Ethernet coax connection File: Robert Johnson.vcf If you have shock level differences between the grounds in two different buildings, either an entire building isn't connected to an earth electrode, or someone is paying a whopping electric bill to heat up mother earth. I suspect the shock situation you were talking about was a power cross condition, either to the cable or within equipment. I hope it was diagnosed and fixed. The voltage differences between two buildings are generally very low, on the order of a couple volts, but due to fractional ohm impedances are capable of very high currents. Building maintenance procedures should routinely be checking for ground currents since they indicate faults in the power system. Note that in accordance with IEC 62102, 10base2 is an SELV circuit and should not be used for exposed plant (between building) wiring. Ethernet distance specs and application recommendations also go against exposed plant wiring. Ethernet 10base5 is considered a TNV-1 circuit and suitable for exposed plant use, is insulated and requires single point grounding. Optical fiber is a better recent development and the best answer for exposed plant lines these days. Note that IEC 62102 provides an extensive list of interconnect circuit types and what category they fit into with regard to shock level (SELV, TNV, hazardous, etc). It's an important reference for any engineer designing interconnect circuits in determining isolation needs. Bob Johnson ITE Safety From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of Knighten, Jim L Sent: Wednesday, March 05, 2003 7:51 PM To: Rich Nute Cc: ken.ja...@emccompliance.com; emc-p...@majordomo.ieee.org Subject: RE: Ethernet coax connection Rich, I think you must be correct. I do have anecdotal evidence of persons being knocked on their butts by grabbing hold of an Ethernet coax in a large facility and trying to connect it to a computer. My experience is in EMC and the 10Base2 Ethernet (coax) is a persistent offender. (Actually, the twisted pair stuff has its own set of EMC problems.) Regards, 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 jim.knigh...@ncr.com -Original Message- From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Wednesday, March 05, 2003 4:31 PM To: Knighten, Jim L Cc: ken.ja...@emccompliance.com; emc-p...@majordomo.ieee.org Subject:Re: Ethernet coax connection Hi Jim: 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. I don't believe the issue is that of electric shock. I don't believe the current and resistance of the neutral are high enough to develop 30 volts (the shock hazard limit). Instead, I believe the problem is that, with two connections, the shield is in parallel with the neutral. That means that some of the neutral current will pass through the shield, and will likely open a PWB trace somewhere. In the process, the PWB trace heating may start a fire. I believe the circuit is: (You may not be able to read this schematic if your mail reader is not set for plain ASCII text.) L
Re: Ethernet coax connection
I read in !emc-pstc that Knighten, Jim L jk100...@teradata-ncr.com wrote (in 61A60D883863D411A36600D0B785B50C0D8C6EC0@susdayte51.daytonoh. ncr.com) about 'Ethernet coax connection' on Wed, 5 Mar 2003: 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. If there is enough voltage to give a 'strong shock', there is far more than enough to pass shield current sufficient to burn the cable up. Ground potential differences are typically sources with milliohm internal impedances. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
RE: Ethernet coax connection
This is a multi-part message in MIME format. If you have shock level differences between the grounds in two different buildings, either an entire building isn't connected to an earth electrode, or someone is paying a whopping electric bill to heat up mother earth. I suspect the shock situation you were talking about was a power cross condition, either to the cable or within equipment. I hope it was diagnosed and fixed. The voltage differences between two buildings are generally very low, on the order of a couple volts, but due to fractional ohm impedances are capable of very high currents. Building maintenance procedures should routinely be checking for ground currents since they indicate faults in the power system. Note that in accordance with IEC 62102, 10base2 is an SELV circuit and should not be used for exposed plant (between building) wiring. Ethernet distance specs and application recommendations also go against exposed plant wiring. Ethernet 10base5 is considered a TNV-1 circuit and suitable for exposed plant use, is insulated and requires single point grounding. Optical fiber is a better recent development and the best answer for exposed plant lines these days. Note that IEC 62102 provides an extensive list of interconnect circuit types and what category they fit into with regard to shock level (SELV, TNV, hazardous, etc). It's an important reference for any engineer designing interconnect circuits in determining isolation needs. Bob Johnson ITE Safety From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of Knighten, Jim L Sent: Wednesday, March 05, 2003 7:51 PM To: Rich Nute Cc: ken.ja...@emccompliance.com; emc-p...@majordomo.ieee.org Subject: RE: Ethernet coax connection Rich, I think you must be correct. I do have anecdotal evidence of persons being knocked on their butts by grabbing hold of an Ethernet coax in a large facility and trying to connect it to a computer. My experience is in EMC and the 10Base2 Ethernet (coax) is a persistent offender. (Actually, the twisted pair stuff has its own set of EMC problems.) Regards, 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 jim.knigh...@ncr.com -Original Message- From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Wednesday, March 05, 2003 4:31 PM To: Knighten, Jim L Cc: ken.ja...@emccompliance.com; emc-p...@majordomo.ieee.org Subject:Re: Ethernet coax connection Hi Jim: 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. I don't believe the issue is that of electric shock. I don't believe the current and resistance of the neutral are high enough to develop 30 volts (the shock hazard limit). Instead, I believe the problem is that, with two connections, the shield is in parallel with the neutral. That means that some of the neutral current will pass through the shield, and will likely open a PWB trace somewhere. In the process, the PWB trace heating may start a fire. I believe the circuit is: (You may not be able to read this schematic if your mail reader is not set for plain ASCII text.) L Bldg A +-++ | || | || | | | | (~) 120 V | | | load | | | | | || |N|| +-++-+-+ |utility | || Bldg A | |ground | || ground | |rod | || rod |PE BNC shield - | | - ++ ---| | --- | - | |-| | | | | | | | | | | | L Bldg B | ++| ||| ||| | | | | | | | load
RE: Ethernet coax connection
Rich, I think you must be correct. I do have anecdotal evidence of persons being knocked on their butts by grabbing hold of an Ethernet coax in a large facility and trying to connect it to a computer. My experience is in EMC and the 10Base2 Ethernet (coax) is a persistent offender. (Actually, the twisted pair stuff has its own set of EMC problems.) Regards, 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 jim.knigh...@ncr.com -Original Message- From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Wednesday, March 05, 2003 4:31 PM To: Knighten, Jim L Cc: ken.ja...@emccompliance.com; emc-p...@majordomo.ieee.org Subject:Re: Ethernet coax connection Hi Jim: 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. I don't believe the issue is that of electric shock. I don't believe the current and resistance of the neutral are high enough to develop 30 volts (the shock hazard limit). Instead, I believe the problem is that, with two connections, the shield is in parallel with the neutral. That means that some of the neutral current will pass through the shield, and will likely open a PWB trace somewhere. In the process, the PWB trace heating may start a fire. I believe the circuit is: (You may not be able to read this schematic if your mail reader is not set for plain ASCII text.) L Bldg A +-++ | || | || | | | | (~) 120 V | | | load | | | | | || |N|| +-++-+-+ |utility | || Bldg A | |ground | || ground | |rod | || rod |PE BNC shield - | | - ++ ---| | --- | - | |-| | | | | | | | | | | | L Bldg B | ++| ||| ||| | | | | | | | load | | | | | ||| | N || ++-+-+| | Bldg B | | | ground | | | rod |PE| - ++ --- BNC shield - You can see from the schematic that the shield is in parallel with both the neutral and the earth-ground. Being in parallel, it will carry some of the neutral current, depending on the respective resistances. Because of both the neutral and the earth-ground, the voltage should never approach 30 volts (1/4 of the mains voltage). But, there can be a very high current in the shield of the BNC cable. Best regards, Rich 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
RE: Ethernet coax connection
Ken, It depends if compliance with the Ethernet standard is important to you. If you connect to anyone else's network where someone else may be dealing with a coax that is grounded on your end, then it is probably important. If not, then it may not matter. This is a product safety issue. I have used 10BaseT (10 Megabit twisted pair Ethernet) in which we shield on both ends within our system. Whatever goes out to the world is not grounded on either end. I am assuming from your messages that this may be a military system, so the product safety rules may be different than for commercial equipment. 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 1:09 PM To: Robert Macy; emc-p...@ieee.org Subject:Re: Ethernet coax connection If all the ac equipment is powered by the same local source, and all the ac powered equipment is case-grounded within the same rack, is it correct to assume that the safety issue is moot? That is, can I then use a grounded bnc connector at both ends? on 3/5/03 4:02 PM, Robert Macy at m...@california.com wrote: It is my understanding there is a spec relating to both the voltage handling capability and the impedance between ethernet coax and earth ground. At low frequency (must be more than a certain level) it is quite high in order to prevent potentially damaging ground loops from forming. At high frequency (must be less than a certain level) to effectively reference the shield to chassis potential and make certain that the coax doesn't radiate. There are manufacturers that sell coax panel connectors with the proper built in capacitor. I recall $10 each price tag. I further recall that we used to use 0.001uF 2kV caps. WELL DRESSED AND MOUNTED EXTREMELY PROPERLY. Vaguely remember that the impedance was to be more than 1Meg at 60Hz and less than 50 at 3MHz, but you should check the ethernet spec. You can tell a lot about the cap's mounting (and quality) by looking at the spectrum of the radiated emissions. For example, internal clock and the cap is referenced to a noisy spot. Or, spectrum related to the ethernet traffic and a loop exists around the coax terminations and bypass cap. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 101 E San Fernando, Suite 402 San Jose, CA 95112 - Original Message - From: Ken Javor ken.ja...@emccompliance.com To: emc-p...@majordomo.ieee.org Sent: Wednesday, March 05, 2003 12:37 PM 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 -- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
RE: Ethernet coax connection
we've had good success with the built capacitance of 9000pf as well, depending on test being discussed and frequency, certain cap. values from the shielded ring of the UNgrounded ring to earth works well for low freq.. 30 mhz. Richard, From: Knighten, Jim L [mailto:jk100...@teradata-ncr.com] Sent: Wednesday, March 05, 2003 4:12 PM To: Ken Javor; emc-p...@majordomo.ieee.org Subject: RE: Ethernet coax connection 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:58 PM To: Knighten, Jim L; emc-p...@majordomo.ieee.org 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 jk100...@teradata-ncr.com 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:38 PM To: emc-p...@majordomo.ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute
RE: Ethernet coax connection
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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:58 PM To: Knighten, Jim L; emc-p...@majordomo.ieee.org 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 jk100...@teradata-ncr.com 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:38 PM To: emc-p...@majordomo.ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
Re: Ethernet coax connection
Jim, Thank you! That took care of my concern. Ken on 3/5/03 4:11 PM, Knighten, Jim L at jk100...@teradata-ncr.com wrote: 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:58 PM To: Knighten, Jim L; emc-p...@majordomo.ieee.org 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 jk100...@teradata-ncr.com 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:38 PM To: emc-p...@majordomo.ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
Re: Ethernet coax connection
If all the ac equipment is powered by the same local source, and all the ac powered equipment is case-grounded within the same rack, is it correct to assume that the safety issue is moot? That is, can I then use a grounded bnc connector at both ends? on 3/5/03 4:02 PM, Robert Macy at m...@california.com wrote: It is my understanding there is a spec relating to both the voltage handling capability and the impedance between ethernet coax and earth ground. At low frequency (must be more than a certain level) it is quite high in order to prevent potentially damaging ground loops from forming. At high frequency (must be less than a certain level) to effectively reference the shield to chassis potential and make certain that the coax doesn't radiate. There are manufacturers that sell coax panel connectors with the proper built in capacitor. I recall $10 each price tag. I further recall that we used to use 0.001uF 2kV caps. WELL DRESSED AND MOUNTED EXTREMELY PROPERLY. Vaguely remember that the impedance was to be more than 1Meg at 60Hz and less than 50 at 3MHz, but you should check the ethernet spec. You can tell a lot about the cap's mounting (and quality) by looking at the spectrum of the radiated emissions. For example, internal clock and the cap is referenced to a noisy spot. Or, spectrum related to the ethernet traffic and a loop exists around the coax terminations and bypass cap. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 101 E San Fernando, Suite 402 San Jose, CA 95112 - Original Message - From: Ken Javor ken.ja...@emccompliance.com To: emc-p...@majordomo.ieee.org Sent: Wednesday, March 05, 2003 12:37 PM 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 -- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
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 jk100...@teradata-ncr.com 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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:38 PM To: emc-p...@majordomo.ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
RE: Ethernet coax connection
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 jim.knigh...@ncr.com -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 12:38 PM To: emc-p...@majordomo.ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
