Re: TNV to Earth Insulation Requirement
Joe, I believe electric strength, clause 5.3, table 18, operation insulation, secondary to body or between independent secondaries, 500 V rms. It is my understanding that he accepted the exemption based on a permanent ground connection, and that the test is necessary if there is no permanent ground connection. Best regards, David. - Original Message - From: j...@aol.com To: gelf...@memotec.com Cc: emc-p...@majordomo.ieee.org Sent: Thursday, December 21, 2000 11:34 AM Subject: Re: TNV to Earth Insulation Requirement Hi David: Thanks for the feedback. Can you elaborate on the reference above to the "500 VAC or 707 CDC requirement"? What clause does this requirement derive from? Was your CSA rep saying that this requirement applies even with a permanent ground, or was he saying that this requirement applies if you do not have a permanent ground? Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
Re: TNV to Earth Insulation Requirement
In a message dated 12/21/00, you write: > He also said that meeting the 500 V ac or 707 V dc requirement was not > Hi David: Thanks for the feedback. Can you elaborate on the reference above to the "500 VAC or 707 CDC requirement"? What clause does this requirement derive from? Was your CSA rep saying that this requirement applies even with a permanent ground, or was he saying that this requirement applies if you do not have a permanent ground? Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
Re: TNV to Earth Insulation Requirement
Joe, Your post came exactly when I was preparing to submit a product powered by -48 V dc source. I have always wondered why it should be necessary to have isolation in this situation, where is the inherent danger? Following your arguments, I submitted this to my CSA rep, who agreed with me providing I could prove the exemptions. He also said that meeting the 500 V ac or 707 V dc requirement was not difficult. -Message d'origine- De : David Gelfand [mailto:gelf...@memotec.com] Envoyé : 12 décembre, 2000 08:45 À : Stephane Objet : Isolation requirements for -48 V permanently connected equipment Stéphane, I am wondering if our -48 V dc equipment could be exempt from isolation requirements. Here are my arguments: 6.2.1.2 "Basic insulation is not required provided that all of the following conditions are met: - the SELV CIRCUIT, TNV-1 CIRCUIT or accessible conductive part is connected to the protective earthing terminal in accordance with 2.5; and -the installation instructions specify that the protective earthing terminal shall have a permanent connection to earth; and - the test of 6.2.1.3 is carried out if the TNV-2 or TNV-3 CIRCUIT is intended to receive during normal" 6.2.1.4 and 6.2.1.5 do not apply to our products. 6.2.2.1 "Exempt from this requirement are: -bare conductive parts ...notmally protected against contact by a cover... -contacts of connectors which cannot be touched by the test probe... 6.3.3.2 Exclusions "The requirements of 6.3.3.1 do not apply to -permanently connected equipment...; or... -equipment that has provision for a permanently connected protective earthing conductor and is provided with instructions for the installation of that conductor. 6.4.1 Separation requirements ...These requirements do not apply where circuit analysis and equipment investigation indicated that safety is provided by other means, for example betwen two circuits each of which has a permanent connection to protective earth. I think we meet these requirements with a protective earthing terminal, instructions and applying ringing voltage for 6.2.1.3. As well, I have been told that central office equipment and large PBXs typically do not have isolation between TNV and SELV/ground. Am I missing something? Do we absolutely have to design for 500 V isolation? I would appreciate your comments. Thank you, David.
Re: TNV to Earth Insulation Requirement
In a message dated 12/12/00, Peter Merguerian writes: > Assume you have equipment with external power earthed (Class 1) power > supply with an earthed appliance inlet for conenction to the mains. The > power supply output is connected to a dc unit with a TNV-2 interface with > no separation to SELV. The dc unit has a earth stud for connection of an > external earthing conductor. All exemptions for basic insulation in Table > 19 is applied. > > My questions is: can the stud on the dc unit serve as my permanent > Hi Peter: Based on your description, my tentative answer would be yes. I'm not sure what the "DC unit" that you refer to is, but the crux of your question seems to be whether it is OK to have a separate grounding lug on the chassis of the equipment that mixes TNV-2 and SELV/ground, as opposed to requiring a hard wired ground associated with the AC power input. The use of the separate grounding lug is quite common on pluggable Type A equipment that needs to qualify for the exemptions under Table 19. I believe that the requirements for the grounding lug are contained in clause 2.5. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
Re: TNV to Earth Insulation Requirement
Dear All, Assume you have equipment with external power earthed (Class 1) power supply with an earthed appliance inlet for conenction to the mains. The power supply output is connected to a dc unit with a TNV-2 interface with no separation to SELV. The dc unit has a earth stud for connection of an external earthing conductor. All exemptions for basic insulation in Table 19 is applied. My questions is: can the stud on the dc unit serve as my permanent connection to earth? UL1950/EN 60 950 Table 19 condition 2 specifies that "the installation instructions specify that the protective earthing terminal shall have a permanent connection to earth". Is the stud the "protective earthing terminal"? What is the definition of "protective earth terminal"? From my understanding, protective earthing terminal is associated with the supply conductors and therefore the appliance inlet earthing terminal is in this case the terminal which must now be changed to have a permanent connection to earth. Is this assumption correct or can the stud on the dc unit serve as the permanent means for connection to the supply? If stud is OK, what is the min. size required? At 17:38 11/12/2000 EST, j...@aol.com wrote: >In a message dated 12/11/00, Dave Lorusso writes: > > >If a telecom product is permanently connected (-48 Vdc Central Office >Equipment), is it exempt from paragraph 6.3.3 Separation of the > I'm reading this as there >is no physical spacing required between TNV and Earth for permanently > > >Is there anything else in UL 1950, IEC 60950, EN 60950, that contradicts >this? > > > > >Hi Dave: > >This topic seems to generate a lot of confusion and controversy, since most >telecom equipment that the test labs see is subject to the isolation > Many test labs seem to be >unaware that the isolation requirements can be waived if certain conditions >are met. > >However, UL 1950 does have provisions for certain types of equipment to not > For example, central office equipment and large PBXs >typically do not have isolation between TNV and SELV/ground. > >The requirements for isolation appear in several clauses in UL 1950 (6.2.1.2, > To qualify for the >exemptions, it is necessary to step through each clause and show compliance > In general, >though, equipment which has a permanently connected earth ground can usually > For clause 6.3.3 that you >mentioned, the permanent ground exemption can be found in clause 6.3.3.2. > >If your equipment qualifies for the exemptions from having isolation, there >should be no requirement for a hipot test between your TNV circuits and > If you plan to exercise the exemptions, I suggest that >you review your rationale ahead of time with your test lab, before they try >to hipot your equipment. > >The requirements in EN 60950 are pretty much the same as UL 1950, except that >Norway and Sweden have additional requirements for the exemption that can be > These requirements call for permanent connection or > This may or may not affect >your product if the input is strictly -48 VDC. > > > >Joe Randolph >Telecom Design Consultant >Randolph Telecom, Inc. >781-721-2848 >http://www.randolph-telecom.com Peter Merguerian Managing Director Product Testing Division I.T.L. (Product Testing) Ltd. Hacharoshet 26, POB 211 Or Yehuda 60251, Israel Tel: 972-3-5339022 Fax: 972-3-5339019 e-mail: pmerguer...@itl.co.il website: http://www.itl.co.il TO LEARN ABOUT AUSTRALIAN AND NEW ZEALAND REQUIREMENTS, CONTACT ME AT THE EARLIEST STAGES OF YOUR DESIGN; REQUIREMENTS CAN BE TRICKY! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: TNV to Earth Insulation Requirement
In a message dated 12/11/00, Dave Lorusso writes: > If a telecom product is permanently connected (-48 Vdc Central Office > Equipment), is it exempt from paragraph 6.3.3 Separation of the > telecommunication network from earth, of UL 1950? I'm reading this as there > is no physical spacing required between TNV and Earth for permanently > connected equipment. How about impulse/hipot requirements? > > Is there anything else in UL 1950, IEC 60950, EN 60950, that contradicts > this? > Hi Dave: This topic seems to generate a lot of confusion and controversy, since most telecom equipment that the test labs see is subject to the isolation requirements between TNV circuits and SELV/ground. Many test labs seem to be unaware that the isolation requirements can be waived if certain conditions are met. However, UL 1950 does have provisions for certain types of equipment to not have this isolation. For example, central office equipment and large PBXs typically do not have isolation between TNV and SELV/ground. The requirements for isolation appear in several clauses in UL 1950 (6.2.1.2, 6.2.1.4, 6.2.1.5, 6.2.2.1, 6.3.3.1, 6.3.3.2, and 6.4.1). To qualify for the exemptions, it is necessary to step through each clause and show compliance with the conditions for which the exemptions are allowed. In general, though, equipment which has a permanently connected earth ground can usually be exempted from the isolation requirements. For clause 6.3.3 that you mentioned, the permanent ground exemption can be found in clause 6.3.3.2. If your equipment qualifies for the exemptions from having isolation, there should be no requirement for a hipot test between your TNV circuits and SELV/ground circuits. If you plan to exercise the exemptions, I suggest that you review your rationale ahead of time with your test lab, before they try to hipot your equipment. The requirements in EN 60950 are pretty much the same as UL 1950, except that Norway and Sweden have additional requirements for the exemption that can be found in Annex ZB. These requirements call for permanent connection or pluggable Type B connection for the AC mains. This may or may not affect your product if the input is strictly -48 VDC. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
TNV to Earth Insulation Requirement
Group, If a telecom product is permanently connected (-48 Vdc Central Office Equipment), is it exempt from paragraph 6.3.3 Separation of the telecommunication network from earth, of UL 1950? I'm reading this as there is no physical spacing required between TNV and Earth for permanently connected equipment. How about impulse/hipot requirements? Is there anything else in UL 1950, IEC 60950, EN 60950, that contradicts this? Thank you, Dave --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
