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 jim.wi...@adtran.com
