Jim - I must admit, your example lost me. Are the HDSL and ISDN on separate cards or not? Are they contained in the same overall equipment shelf/enclosure? Are they sharing a modular jack? If so, by what arrangement and who (mfg. or telco) set it up that way?
Regards, Peter L. Tarver Nortel [email protected] > ---------- > From: JIM WIESE[SMTP:[email protected]] > Sent: Wednesday, April 29, 1998 1:47 PM > > Thanks Peter for the excellent response. I'll take the challenge and > extend the thread. > > Suppose you are network equipment, and your customer is a U.S telco or > you want to sell the product to an international telco. Your equipment > is strictly Central Office equipment, not CPE. > > Your customer requires a Listing to UL 1950 3rd Edition or EN 60950 (for > Europe). > > They are also requiring the use of amp champ telco connectors like those > used on most channel banks. > > Secondly suppose that your equipment meets basic (2.0mm at 200 VDC, > Bellcore maximum for Class A3) everywhere except at the pins of an amp > champ connector. All circuits have basic insulation (except the champ > connector) and a fault of deficient spacings at the amp champ connector > results in a fault between a 190 VDC HDSL circuit and a ISDN TNV 1 > circuit. The ISDN card TNV 1 has basic insulation to SELV and the HDSL > card has basic insulation to SELV. Since they are in adjacent slots of > the equipment, The TNV 1 and the 190VDC HDSL cards have their tips and > rings appear on adjacent pins of the amp champ connector. A fault of > the 190VDC HDSL onto the TNV 1 ISDN line would only appear on the > network going toward the end customer. The ISDN customer now gets > something unexpected (i.e. 190VDC). The telco employees are protected > as the basic insulation protects their SELV. > > Is the amp champ connector required to provide basic insulation onto the > network eventhough the MDF's, splices crossconnects etc. do not provide > 2.0mm of insulation? If so what is the rational? > > Thanks, > > > > > Jim > > Jim Wiese > ADTRAN, INC. > 901 Explorer Blvd. > P.O. Box 140000 > Huntsville, AL 35814-4000 > 256-963-8431 > 256-963-8250 fax > [email protected] > > >---------- > >From: Jon D Curtis[SMTP:[email protected]] > >Sent: Wednesday, April 29, 1998 12:24 PM > >To: [email protected] > >Subject: BOUNCE [email protected]: Non-member submission from > ["Peter > >Tarver" <[email protected]>] (fwd) > > > >From: "Peter Tarver" <[email protected]> > >Subject: RE: UL 1950 3rd, and IEC 950 > > > >As with many things in life, there is no simple answer to your whole > >question list, but I'll address what I can in a short form. > > > >A telco is a utility and normally a monopolistic entity. The systems and > >equipment the telco use are maintained (supposedly) to a much higher > degree > >(at least inside the CO) than equipment in a users premises (software > >blunders, fires in battery rooms and ignored alarms of recent years > aside). > >This is because the utility, at least in the US, is required to maintain > >highly reliable service to remain exempt from antitrust laws. Service > >interruptions are inevitable, but you get the drift. Likewise, in the > US, > >the telco is exempt from complying with the NEC. I don't know how their > >relationship with OSHA works > > > >In cases where the telco might still be owned by the government, it's no > >surprise that they exempt themselves from the same laws, edicts, etc., > that > >they subject industry or the public at large to. > > > >Both TNV-1 and TNV-3 are subject to the same assumed 1.5kV transient > level. > >The primary difference lying in the presence of alerting signals for > TNV-3. > >The alerting signals are desired to remain off of TNV-1 and SELV > circuits, > >where it is expected to have only safe to touch (in the former sense of > the > >950 based standards) normal operating voltages. The TNV-3 should then be > >separated by some level of insulation. Since the voltage levels for > TNV-3 > >far exceed those normally present in TNV-1 and would at one time have > been > >called hazardous in the context of the 950 based standards, the level of > >insulation called for would be at least Basic for reliably earthed > circuits > >and Supplementary and/or Reinforced for cases where one or more circuits > are > >unearthed. > > > >Knowing that the typical current levels are low for alerting signals when > >compared to the unrestricted current levels that can be associated with > >Hazardous Voltages, there is reasonable rationale to allow a reduction of > >the otherwise required insulation for the general case of unearthed or > >"unreliably" earthed circuits to Basic. Where earthing and other > criteria > >are met, even Basic insulation can be waived (refer to the Conditions > >applicable to Table 19). > > > >As to your last question, I don't think the standards writers assumed > >miswiring by the telco, though they may have recognized the possibility > >(still, I could be wrong). The EST isolation requirements between TNV-1 > and > >TNV-3 are more likely based on TNV-1 being most often derived from SELV > >circuits. It seems preferable to require Basic between TNV-1 derived > from > >an unprescribed source voltage and TNV-3 than to require Basic insulation > >between SELV and TNV-1. > > > >Don't forget, Pluggable Equipment Type A not installed by Service > Personnel > >used to need Supplementary insulation from TNV of any type to earthed > parts > >(and still does in Sweden). At least Basic doesn't have through > insulation > >thickness requirements. > > > >Maybe I haven't satisfactorily answered your question; maybe I've added a > >little grist to the mill. It will be interesting to see how this thread > >progresses. > > > >Regards, > > > >Peter L. Tarver > >Nortel > >[email protected] > > > >> ---------- > >> From: JIM WIESE[SMTP:[email protected]] > >> Sent: Wednesday, April 29, 1998 6:01 AM > >> > >> I am looking for some guidance in understanding the separation > >> (creepage/clearance) requirements with regard to TNV circuits in UL > 1950 > >> 3rd and IEC 950 and its derivatives. > >> > >> Why is there a requirement that TNV circuits have basic insulation > >> between TNV1 and TNV3 circuits? > >> > >> I am asking the question for the following reasons: > >> > >> The telco network provider is generally exempt from listing > requirements > >> altogether. They have no restrictions on separation of circuits and > >> have TNV 1, TNV 3 and span powered circuits (200 VDC HDSL, T1 etc.) > >> intermingled at the central office in channel banks, cross connects > etc. > >> They provide these services via cables that are spliced, cross > >> connected and intermingled in the Outside Plant. They are also > >> intermingled without regard to spacings at the distribution and > >> demarcation points. Since it is a fact that these services are not > >> separated by "basic" insulation, why would it be important to separate > >> TNV1 and TNV 3 in the terminating equipment. To me it seems like a > >> chain made of paper, and at the end of the chain the standards are > >> requiring a steel link. > >> > >> Secondly, do the standards assume that faults of TNV 1, TNV 3, and > other > >> high voltage telco services could be faulted by the telco provider > >> inadvertently and therefore this type of fault is accounted for by the > >> dielectric test (and other restrictions) between SELV/chassis and TNV > 1, > >> and TNV 3. > >> > >> Any input would be appreciated and helpful. > >> > >> Thanks, > >> > >> Jim > >> > >> Jim Wiese > >> ADTRAN, INC. > >> 901 Explorer Blvd. > >> P.O. Box 140000 > >> Huntsville, AL 35814-4000 > >> 256-963-8431 > >> 256-963-8250 fax > >> [email protected] > >> > > > > >
