Rob I'll try to keep my answers short and to the point.
1) Standard is very clear, test of 6.1.2.1 is not required since you are bonding the unit to earth and providing clear installation instructions that specify that. 2) Coax is typically regarded as SELV since it is not used for TNV type of interfaces in 60950. For example the E1/T1 coax 75Ohm interface is never subjected to Overvoltage since it resides with in the building only. Same applies to DS3 or other interfaces. This is a typical mistake by compliance engineers in differentiating between SELV and TNV1. If a line is called E1 or T1 it does not imply that it is TNV-1. Actually most E1/T1s on the market are SELV because of the application they are used in. Regards ---------------------------------------------------------- Ilan Cohen Technical Director, Safety & Telecom Divisions I.T.L (PRODUCT TESTING) Ltd. 26 Hacharoshet St, POB 211, Or Yehuda, Israel. Tel 972-3-5339022, Fax 972-3-5339019 [email protected], website: http://www.itl.co.il ------------------------------------------------------------ -------------------------------------------------------------------------------------------------------- I-SPEC: The best place on the internet to learn about safety !! http://www.i-spec.com/ (I-Spec is provided free of charge as a service by ITL to the compliance community) --------------------------------------------------------------------------------------------------------- -----Original Message----- From: Robert Johnson [ mailto:[email protected]] Sent: Wednesday, November 26, 2003 5:27 PM To: [email protected] Subject: IEC 60950 Clause 6 questions 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
