I appreciate your comments, and I did not imply telco's do not provide protection. In fact they do a great job. However the spacings on an AT&T D4 channel bank (for instance, I could list endless others) are less than .3mm from the tip/ring of one channel to the tip/ring of another channel (look at the spacings of the "amp champ" pins). Since adjacent channels can have cards that are TNV1, TNV2, TNV3, or Hazardous voltage secondary circuits (190VDC fractional T1), separation is <.3mm. According to UL 1950 3rd edition, the creepage at 190VDC is 2.0mm (1.5mm at 120VDC). .3mm is substantially deficient with regard to UL 1950 3rd edition. In other words the network has <.3mm between different TNV's at the C.O., yet UL 1950 3rd Edition would require 2.0mm at the terminal device. What is the point if the network is deficient in spacing. Also network equipment that happens to be evaluated for a listing is almost surely done to UL 1459 or a UL category such as "DUZO". The only thing required is a dielectric test, not spacings. By the way, .3mm will pass a 1000VAC dielectric in most cases.
I would also be very interested in information regarding any Bellcore document that addresses spacings between adjacent circuits. The only thing I can find is a dielectric test for embedded power supplies that requires 1000 VAC between the embedded power supply and the telco network. Bellcore GR-1089-CORE does not address this, but only requires equipment to pass the Lightning and Power Fault tests in section 4. 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: Jan Purwin[SMTP:[email protected]] >Sent: Wednesday, April 29, 1998 10:13 AM >To: [email protected] >Subject: Re: UL 1950 3rd, and IEC 950 > >Jim you are not quite right. >There is a lot of protection and separation that are defined in NEBs and >NEDS standards. >Those are incorporated into the equipment that is installed in a central >office. > >If you have a chance to go to typical central office and look how RBOC >installes equipment you would >had better idea about protection separation and equipment construction that >goes into CO equipment. >Jan Purwin > >JIM WIESE wrote: > >> 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] > > > >
