Hello All, I have to agree that there shouldn't be another US (UL) standard for network equipment when the equipment can be incorporated into UL1950. UL1950 can be revised to clarify the network equipment requirements, perhaps as a "deviation" or an "appendix" (annex), or just rewording the existing sections to make it easier to follow. I think the network equipment has proven its safety over time, and UL, by having a UL1459 standard implies they agree, along with Telcordia (Bellcore) (GR-1089). It shouldn't be much of an issue to clarify UL1950 to include network equipment constructions. Reviving UL1459 only opens the door to confusion, making it more difficult to achieve a "worldwide" certified piece of equipment. We want to move towards harmonization worldwide, we don't want to increase the gap. I'm also afraid we would wind up adding "UL1459 Listed" to our long list of certifications on the back of the equipment! I hope this helps. Regards, Bob Tims Compliance Engineer Ericsson Messaging Systems Inc.
Peter Merguerian wrote: > Jim, > > Your interpretaion is 100% correct. I have personally Listed many > products with UL1950 Third Edition with a supplemental earthing > terminal as you described below with no basic insulation between > the TNV-2/TNV-3 circuits and SELV/Earth. > > The standard specifies that basic insulation is one way of > complying with the requirements. Another way is as you describe > in your e-mail and which I have used to Approve lots of equipment > worldwide. However, the standard goes on to say "other solutions > are not excluded". > > My question to you all does anyone have a design or could give > some examples using "other solutions are not excluded"? > > PS - The IEC 950 WG7 Committe (Telecoms) is currently working > on Remote Power Feeding Requirements. Some members of the > committe are also from the US and Canada. We are working > together to come up with solutions. A lot of work still remains and I > am hopeful that within 2 years we should have common > requirements (of course as usual, with deviations for member > countries). I strongly feel that there is really no need to come up > with a new standard for network equipment since the UL1950 will > eventually have the remote power feed requirements included. > > Best Regards, > > > In a message dated 3/24/99, jim.wi...@adtran.com writes: > > > > > The only design criteria with regard to insulation in Bellcore standards > > > or > > UL 1459 is a hi-pots test. > > > Creepage and clearance do not exist in traditional C.O. equipment (just > > > look > > at wire wrapped > > > backplanes). > > > > > > Dear Jim and others: > > > > Jim Wiese has raised several concerns regarding the transition from UL 1459 > > to > > UL 1950 (3rd Edition). One of these concerns relates to the new creepage > > and > > clearance requirements for separation of TNV circuits and ground/SELV. > > > > I would like to pick up on this one issue (I know that Jim has raised > > several > > other issues as well). In particular, I would like some feedback from > > others > > in the group regarding my interpretation of how the separation requirements > > in > > UL 1950 apply to certain types of equipment. > > > > Just this week I met with a PBX manufacturer who is in the process of re- > > designing the backplane and all of the line cards in their PBX to "comply > > with > > UL 1950." The PBX is presently approved to UL 1459, but the manufacturer > > has > > its eye on the March 2000 date for new or modified products to comply with > > UL > > 1950. Needless to say, the redesign effort is an expensive one. > > > > The biggest headache in the redesign is complying with the creepage and > > clearance distances for separation of TNV and SELV circuits. The PBX > > manufacturer seemed incredulous when I stated that I did not think the > > creepage and clearance requirements applied to their product, since the PBX > > has a permanent (hardwired) connection to ground. My interpretation is > > based > > primarily on the following statement in clause 6.2.1.2 in UL 1950, > > paraphrased > > below: > > > > " Basic insulation is not required provided that all of the following > > conditions are met: > > - the SELV circuit .... is connected to protective earth...in accordance > > with 2.5; and > > - the installation instructions specify....a permanent connection to > > earth; > > and > > - the test of 6.2.1.3 is carried out... (where applicable)" > > > > There are other clauses that call out isolation, such as 6.3.3.1 and 6.4.1, > > but the "permanent ground" exemption appears to apply here as well. > > > > In my view, these exemptions are specifically targeted at equipment such as > > PBXs and network equipment that are typically installed by service personnel > > and include hardwired grounding. Without these exemptions, it is almost > > impossible to separate certain types of TNV circuits from SELV and ground. > > For example, a feed circuit that provides 48V battery (SLIC, FXS, DID, etc.) > > is inherently referenced to ground. The situation with a ground-start FXO > > interface is not much better. > > > > Do others in the group agree with this interpretation? If not, how are feed > > circuits supposed to be isolated? Does anyone have direct experience with > > getting a product through UL with these exemptions? > > > > I recognize that the original thread here related to network equipment, but > > the "permanent ground" exemption should apply to network equipment as well. > > I > > also recognize that these exemptions only apply to circuits that qualify as > > TNV, and do not address some of the other issues that Jim Weise raised > > concerning things like 200 volts DC for repeaters. However, for simple TNV > > isolation, it seems that network equipment could use the "permanent ground" > > exemptions from having to provide creepage and clearance (or in fact, any > > isolation at all). > > > > Any input from others in the group would be welcome. > > > > > > Joe Randolph > > Telecom Design Consultant > > Randolph Telecom, Inc. > > 781-721-2848 (USA) > > > > --------- > > This message is coming from the emc-pstc discussion list. > > To cancel your subscription, send mail to majord...@ieee.org > > with the single line: "unsubscribe emc-pstc" (without the > > quotes). For help, send mail to ed.pr...@cubic.com, > > j...@gwmail.monarch.com, ri...@sdd.hp.com, or > > roger.volgst...@compaq.com (the list administrators). > > > > PETER S. MERGUERIAN > MANAGING DIRECTOR > PRODUCT TESTING DIVISION > I.T.L. (PRODUCT TESTING) LTD. > HACHAROSHET 26, P.O.B. 211 > OR YEHUDA 60251, ISRAEL > > TEL: 972-3-5339022 > FAX: 972-3-5339019 > E-MAIL: pe...@itl.co.il > Visit our Website: http://www.itl.co.il > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to majord...@ieee.org > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to ed.pr...@cubic.com, > j...@gwmail.monarch.com, ri...@sdd.hp.com, or > roger.volgst...@compaq.com (the list administrators).
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