Joe, If that exemption were not there, the connection between mouse and PC I would understand as TELECOMMUNICATION NETWORK. Lighting cause ground differences so I do not suppose underground cables being free of lighting transients. The question left: If my connection is the TELECOMMUNICATION NETWORK then my circuit is TNV-1 but does it work in opposite direction ? If I classify my circuit as TNV-1 do I need to read Cl. 6 ? Piotr Gałka
----- Original Message ----- From: Joe <mailto:j...@randolph-telecom.com> Randolph To: Piotr Galka <mailto:piotr.ga...@micromade.pl> ; EMC-PSTC <mailto:emc-p...@ieee.org> Sent: Monday, September 11, 2006 10:18 PM Subject: Re: EN 60950-1 RS485 and TNV-1 On 9/11/2006, Piotr Galka wrote: If I connect two devices located in the same building by RS485 I understand they both are SELV. But what if I connect devices located in separate buildings ? Hi Piotr: This topic was discussed recently on this board. I believe that the exemption for "SELV circuits connecting units of information technology equipment" was inserted in 1.2.13.8 to cover the type of situation that you describe. Unfortunately, it becomes a matter of judgement as to whether such a cable might be subject to lightning transients. If the cable run is very short and is run underground, you could probably argue that it is not subject to lightning transients and it can be classified as SELV. However, if the cable run may be long and/or it may be strung above ground, it is probably wise to classify it as TNV-1. The final decision about how to classify the cable will rest with you and your safety test agency. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) j...@randolph-telecom.com http://www.randolph-telecom.com <http://www.randolph-telecom.com/> ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
