I received a couple of notes to advise me of an error in my e-mail. I was intercepted at my desk midthought and should have not sent he e-mail until I had a chance to proof it. When T1 is isolated from the network, it is indeed SELV. It is TNV-1 when not so isolate.
My apologies. Regards, Peter L. Tarver, PE Product Safety Manager Sanmina Homologation Services peter.tar...@sanmina.com > -----Original Message----- > From: owner-emc-p...@majordomo.ieee.org > [mailto:owner-emc-p...@majordomo.ieee.org]On > Behalf Of Peter Tarver > Sent: Tuesday, October 23, 2001 1:01 PM > To: emc-p...@majordomo.ieee.org > Cc: j...@aol.com; phopk...@ga.conklincorp.com > Subject: RE: TNV Circuits > > > > Perry - > > A note of general concurrence with Joe's take on your > circuits. The various DSL power feeds are at this time > treated as hazardous voltage circuits. There is > activity in > IEC, TC47, to consider requirements for remote feeding > circuits, but publication is not imminent. > > The UL/CSA allowance for legacy CO equipment uses > an Outline > of Investigation and is referred to on UL's web > site. There > was a separate product category established for retrofit > equipment intended to service the installed base > infrastructure. Details can be found in UL's 31JAN2001 > Bulletin to Industry. I can forward a copy to interested > parties. > > T1 circuits, if isolated from the network by a CSU or > similar equipment in accordance with CSA or > UL60950, will be > TNV-1. If span powering is present, the T1 > circuit is also > likely to be classed as hazardous voltage (+/-130Vdc, if > memory serves, exceeding the 120Vdc with current limiting > Joe mentioned). > > Regards, > > Peter L. Tarver, PE > Product Safety Manager > Sanmina Homologation Services > peter.tar...@sanmina.com > > > From: j...@aol.com > > Hi Perry: > > If you have the reported 190 VDC span powering on your DSL > lines, you may well be forced into the hazardous voltage > category. In clause 2.3.1(b), UL 60950 limits > TNV voltages > to 60 VDC, with voltages up to 120 VDC allowed if current > limiting is included. Clause 3.5.3 allows central supply > voltages up to 80 VDC to be declared TNV-2 under certain > circumstances. However, voltages of 190 VDC exceed any > definitions of TNV that I am aware of. > > The issue of span powering and the requisite insulation > requirements created quite a commotion a year or two ago > when the Second Edition of UL 1950 was about to become > mandatory. As written, the Second Edition would have > rendered noncompliant a wide range of T1 > equipment that was > widely deployed and still in production. As I recall, the > effort to bring this to UL's attention was led by Adtran. > > I seem to recall seeing a document that was worked out > between the industry and UL to address the legacy products > that used high voltage span powering. I do not recall the > details, but if it would be helpful I can look into it for > you. I do not know whether the agreement that was reached > for these legacy products could be applied to your > situation. > > > Joe Randolph > > > > In a message dated 10/23/01, Perry Hopkins writes: > > > My question is; by definition, shouldn't the DSL circuits > fall under the TNV-3 and not Hazardous Voltage secondary > circuit. The major difference is when you are determining > the creepage and clearance distances. At TNV-3 you are > allowed basic insulation between TNV-3 circuits and SELV > circuits but at the Haz Voltage Reinforced insulation is > required. > > > > ------------------------------------------- > 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: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. ------------------------------------------- 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: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
