I have a couple questions about the use of Clause 6 of IEC 60950. First: In order to pass the “Pass 6.1.2” block, the test of 6.1.2 is applied. A voltage of 120 volts is used for figure 6A. If a grounded circuit is used, and the exclusions of 6.1.2.2 apply, then the test of 6.1.2.1 is not used. Is this correct, or is the test of 6.1.2.1 applied regardless of the exclusions in 6.1.2.2? The wording in note 4 appears ambiguous on this point.
Second: When using coaxial cable for TNV-1 purposes, I have trouble figuring out how to apply clause 6. A typical example is “fiber to the curb” where the final service drop from the pole to the subscriber is made with small coax such as T3 lines. The cable shield is grounded at the equipment 6.1 can be passed by having the serviceman ground the equipment (6.1.2.2). 6.2 can be passed by grounding both TNV and SELV. 6.3 is passed since no power is applied to the TNV circuit. 6.4 is a problem however since primary and secondary protectors are not used. The central path of figure 5C can be used for compliance since the coax is greater than 26 AWG, the circuit is grounded, and an enclosure and spacings are provided. However, this does not solve the problem of a power cross where up to 25 amps (-or more; I believe this figure came >from the twp lines) may be carried into the building to the equipment on the coax, overheating the telecom cable. Have I overlooked some requirement or does the standard avoid addressing this problem? Is there a suggested solution: The only one I can think of is adding a ground at the service entrance and fusing the shield, but this is not a current practice. Bob Johnson ITE Safety This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
