Dear collegues, I have a question about clause 6.4.1 of IEC950/A1/A2/A3/A4. This clause deals with protection of operators against lightning coming on TNV-1 or TNV-3 lines. In paragraph b), it is required that a pulse test must be made between TNV-1 or -3 and "parts that can be touched by the testfinger". I assume that an enclosure made of metal, and that contains these circuits, is a "part that can be touched". Further-on, this clause mentions that "these requirements do not apply where it is shown that safety is provided by other means, for example between circuits each of which has a permanent connection to earth".
My assumption: >From my point of view, I assume that the lightning is supposed to enter the system in common mode. My question: If the above assumption is correct, is it allowed not to perform this test if the metal enclosure is earthed in case of: - a permanent earth connection made by service personnel? - a connection made with a plug like Pluggable equipment type A? The same clause, par. c) deals with isolation between TNV-1 or -3 and "circuitry that is provided for connection to other equipment". If this interface circuit (SELV in my case) is electrically "far away" from TNV-1 or -3, which means that a lot of electrical ground connected to PE is between both of them, is it then not possible not to perform this test? I'm still convinced that a real lightning pulse is looking for a solid ground (PE) as a return path and not an SELV interface. Is there a difference regarding the way the grounds (PE) are connected, permanent or pluggable ? When, during the pulse-test, there is a spark-over from TNV-3(1) to PE, is this allowed? Kind regards and really looking forward to Your opinion! Carpentier Kris Alcatel Telecom Fr. Wellesplein B-2018 Antwerp - Belgium tel.: 32 3 240 7986 fax.: 32 3 240 9933 email: [email protected] ref:kcarpentier/[email protected]
