That’s an interesting question, and I do not know the answer, despite having been involved with designing telecom equipment for 40 years. The fact that this issue has never crossed my radar suggests that phone line cords are not subject to the same marking requirements as AC mains cords.
It’s worth noting that while telephone ringing voltages can reach 86 VRMS (superimposed on an additional 50 VDC), they are *not* classified as hazardous voltages under EN 60950. When telecom line voltages were first being incorporated into IEC 60950, the initial classification proposed by the authors was “hazardous” because it seemed it should be classified that way. However, the telecom industry pushed back with the argument that no one had ever been injured by ring voltages and that classifying them as hazardous would create a lot of problems by instantly invalidating many long-term industry practices. The solution was a compromise that created a new classification called Telecom Network Voltage (TNV). There are actually three levels of TNV, but an ordinary phone line with ringing is classified as TNV-3. The definition is rather tortuous as described in Annex M of 60950, but the basic reasoning for the new classification relies on two criteria: 1) The ring voltage includes silent intervals that allow a let-go response if contacted 2) The current that can be delivered is limited to a low value This awkward compromise has served well for many years. Technically, the ringing signals on an ordinary phone line are not classified as “hazardous.” Rather, they are classified as “TNV-3.” Perhaps this has something to do with the way ordinary phone cables are regulated. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) <mailto:[email protected]> [email protected] <http://www.randolph-telecom.com> http://www.randolph-telecom.com From: Scott Xe [mailto:[email protected]] Sent: Tuesday, June 06, 2017 12:15 AM To: [email protected] Subject: [PSES] Telephone extension cable I did some search on the telephone cable specs that do not state to withstand high voltage and just state voltage 30 V and insulation 50 Mohms/km. As the ring comes in, the line may carry a 90 Vrms, 20 Hz AC signal, does this device fall into LVD like mains cordset in EU? Thanks and regards, Scott - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected] <mailto:[email protected]> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected] <mailto:[email protected]> > Mike Cantwell <[email protected] <mailto:[email protected]> > For policy questions, send mail to: Jim Bacher <[email protected] <mailto:[email protected]> > David Heald <[email protected] <mailto:[email protected]> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
