Peter, I am very glad you made these points and they are very valid with regard to TNV 1, TNV 2, and TNV 3. They should help many vendors overcome some gray issues in UL 1950.
I am also happy that you opened this discussion up to the remote power feed standard that is expected to be pulled into UL 1950 (UL 60950) probably by next year. The remote power feed standard , if adopted, and pulled into UL 1950, will essentially obsolete almost all channel banks, shelves and housings used for transmission by the RBOC's, GTE and Canadian telco providers. Not only is the loop current limited to under 60 mA, there is an ABSOLUTE requirement for "reinforced insulation" which is equivalent to 4.0mm based on Bellcore's Class A3 limits. Last year we investigated the connectors and backplanes of over 20 of the most popular shelves, housings and channel banks and found this creepage to range from roughly .5mm to 2.0mm. This was on currently available T400/T200, 220, DDM+, 3192 shelves and D4, D5, SLC 5, SLC 2000, and other banks that I cannot mention. Many were listed to UL 1459. These hosts are the backbone for phone companies to deploy ISDN, HDSL, HDSL-2, extended range DDS, extended range ISDN, T1, etc. They also support TNV-1, TNV-2, and TNV-3 deployment. As I mentioned before, we are perfectly willing to let the chips fall where they may. We can design and build UL 1950 compliant channels banks and housings all day and make good money doing it. However, we feel it is important to point out to our partners at the RBOC's, GTE, Bell Canada, etc. that they are about to be taken for a ride they don't want to take. They have perfectly good safe equipment that has 20 or 30 years left in it. If nothing is done to address this situation they will not be able to buy "listed" new technologies to put in these channel banks, shelves, and housings after March 15th, 2000, and they can only buy previously "UL 1459 listed" technologies until March 15th 2005 unless something is done at the standards level or NRTL's waive creepage and clearance for this type of equipment. On a long final note, I will re-emphasize that network equipment is not covered in the scope or intent of UL 1950. Although if equipment can meet the requirements of UL 1950, then by all means IT SHOULD HAVE THAT OPTION. Here is an example to ponder: Section 6 of UL 1950 is titled "Connection to Telecommunications Networks". It states that section 6 covers circuitry that is to be connected to a "Telecommunications Network" and this circuitry consists of a "SELV" or "TNV" circuit (only). Section 1.2.14.7 defines a "Telecommunication Network" and gives examples in note 3 of a public switched telephone network, public data network, and ISDN network. It is clear that the intent of the standard was to address consumer ITE equipment connecting to the network, not network equipment that will eventually connect to consumer equipment. The key words are "connecting TO a Telecommunications Network". This is analogous to FCC part 68 which only covers equipment connecting TO the Network, not which make up the network. UL 1950 is making no attempt to evaluate the design, methodology or safe construction methods of equipment that makes up the ISDN or switched public network. This meshes perfectly with my first E-mail in which I pointed out UL 1950 does not even cover network equipment in its scope statement. If the above is not true then in UL 1950's eyes, the phone companies cannot deploy HDSL, ISDN (with repeaters), DDS (with repeaters), T1 (with repeaters), HDSL -2, etc as none of these fit the requirements of a SELV or TNV circuit as stated in 6.2 a, b, or c as the voltage is continuously greater than 60 volts DC and can have unlimited current to ground at 80VDC (Bellcore GR-1089-CORE Class A2), or 140VDC(Class A3). Many of these technologies utilize ground fault detect circuitry and operate at -200 VDC to ground. These technologies are considered Hazardous Voltage Secondary Circuits per UL 1950 and cannot go out on the network. As such UL 1950 does not even attempt to describe the "network". Of course we all know the phone companies drop this HVSC down to SELV or TNV limits prior to the customer side of the demarcation point. I vote for a standard or listing category that allows "network" equipment to be listed if it meets either the requirements of UL 1950 or UL 1459. I would also personally like to see the constructional method for overvoltage in table 18d of UL 1950 eliminated for this standard or category so that it meshes with the 2nd level power fault exemption in Bellcore GR-1089-CORE. Thanks for all the responses so far, it should definitely create some interesting discussions at the TIA TR 41.7.1 meeting in Portland, OR. in May. Jim Jim Wiese Compliance Engineer ADTRAN, INC. 901 Explorer Blvd. P.O. Box 140000 Huntsville, AL 35814-4000 256-963-8431 256-963-8250 fax [email protected] > ---------- > From: [email protected][SMTP:[email protected]] > Sent: Thursday, March 25, 1999 2:49 PM > To: emc-pstc; 'TREG'; [email protected] > Cc: [email protected] > Subject: Re: Network Equipment and UL 1459/1950 > > 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, [email protected] 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 [email protected] > > with the single line: "unsubscribe emc-pstc" (without the > > quotes). For help, send mail to [email protected], > > [email protected], [email protected], or > > [email protected] (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: [email protected] > 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 [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
