Dear All, Assume you have equipment with external power earthed (Class 1) power supply with an earthed appliance inlet for conenction to the mains. The power supply output is connected to a dc unit with a TNV-2 interface with no separation to SELV. The dc unit has a earth stud for connection of an external earthing conductor. All exemptions for basic insulation in Table 19 is applied.
My questions is: can the stud on the dc unit serve as my permanent connection to earth? UL1950/EN 60 950 Table 19 condition 2 specifies that "the installation instructions specify that the protective earthing terminal shall have a permanent connection to earth". Is the stud the "protective earthing terminal"? What is the definition of "protective earth terminal"? From my understanding, protective earthing terminal is associated with the supply conductors and therefore the appliance inlet earthing terminal is in this case the terminal which must now be changed to have a permanent connection to earth. Is this assumption correct or can the stud on the dc unit serve as the permanent means for connection to the supply? If stud is OK, what is the min. size required? At 17:38 11/12/2000 EST, j...@aol.com wrote: >In a message dated 12/11/00, Dave Lorusso writes: > > >If a telecom product is permanently connected (-48 Vdc Central Office >Equipment), is it exempt from paragraph 6.3.3 Separation of the > I'm reading this as there >is no physical spacing required between TNV and Earth for permanently > > >Is there anything else in UL 1950, IEC 60950, EN 60950, that contradicts >this? > > > > >Hi Dave: > >This topic seems to generate a lot of confusion and controversy, since most >telecom equipment that the test labs see is subject to the isolation > Many test labs seem to be >unaware that the isolation requirements can be waived if certain conditions >are met. > >However, UL 1950 does have provisions for certain types of equipment to not > For example, central office equipment and large PBXs >typically do not have isolation between TNV and SELV/ground. > >The requirements for isolation appear in several clauses in UL 1950 (6.2.1.2, > To qualify for the >exemptions, it is necessary to step through each clause and show compliance > In general, >though, equipment which has a permanently connected earth ground can usually > For clause 6.3.3 that you >mentioned, the permanent ground exemption can be found in clause 6.3.3.2. > >If your equipment qualifies for the exemptions from having isolation, there >should be no requirement for a hipot test between your TNV circuits and > If you plan to exercise the exemptions, I suggest that >you review your rationale ahead of time with your test lab, before they try >to hipot your equipment. > >The requirements in EN 60950 are pretty much the same as UL 1950, except that >Norway and Sweden have additional requirements for the exemption that can be > These requirements call for permanent connection or > This may or may not affect >your product if the input is strictly -48 VDC. > > > >Joe Randolph >Telecom Design Consultant >Randolph Telecom, Inc. >781-721-2848 >http://www.randolph-telecom.com Peter Merguerian Managing Director Product Testing Division I.T.L. (Product Testing) Ltd. Hacharoshet 26, POB 211 Or Yehuda 60251, Israel Tel: 972-3-5339022 Fax: 972-3-5339019 e-mail: pmerguer...@itl.co.il website: http://www.itl.co.il TO LEARN ABOUT AUSTRALIAN AND NEW ZEALAND REQUIREMENTS, CONTACT ME AT THE EARLIEST STAGES OF YOUR DESIGN; REQUIREMENTS CAN BE TRICKY! ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
