Dear Tregers and Nebers I am sure that most of you are familiar with the EN/UL 60950 requirement for isolation between TNV circuits and SELV circuits.
If we define the DC power circuits as TNV-2 or SELV (as allowed by the third edition of IEC60950), than we need Basic isolation between the power circuits and the TNV1/3 circuits. This isolation between TNV1/3 and the DC power source can be waived as long as there is Permanent bonding to earth of the SELV/TNV-2 and the TNV-1 circuit. Now to the problem…… TNV-1/3 circuits must be a floating circuits. This means they cannot be earthen by definition. In T1/E1 circuits there is ground provided through a central tap of the T1/E1 transformer. Can such a circuit be considered "bonded to earth circuit"? Since the E1/T1 does not seem to be truly bonded to earth than Basic insulation will be required. And much of the T1/E1 circuits residing in central offices and applying DC voltages to the T1/E1 (wetting current) is NON compliant?!? Thanks Ilan ---------------------------------------------------- Ilan Cohen Manager, Telecom Division I.T.L (PRODUCT TESTING) Ltd. 26 Hacharoshet St, POB 211, Or Yehuda, Israel. Tel 972-3-5339022, Fax 972-3-5339019 ico...@itl.co.il, website: http://www.itl.co.il ----------------------------------------------------
