We just completed an approval with the exact same situation. I cannot speak for your prodcut since I have not reviewed it. I can provide a contact at UL if required.
One of the big concerns is the R/C connectors normally used for bringing the lines in do not even meet UL1950 unless pins are skipped. Best Regards, Jody Leber jle...@ustech-lab.com http://www.ustech-lab.com U. S. Technologies 3505 Francis Circle Alpharetta, GA 30004 770.740.0717 Fax: 770.740.1508 -----Original Message----- From: j...@aol.com [SMTP:j...@aol.com] Sent: Wednesday, March 24, 1999 3:42 PM To: emc-pstc; 'TREG' Cc: jim.wi...@adtran.com Subject: Re: Network Equipment and UL 1459/1950 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). --------- 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).
