In a message dated 9/12/01, David Drori writes: > It indeed looks as though digital telephones are SELV devices. However, I > wonder what the legal basis would be. Surely, it would be insufficient to > just measure the voltages on the cable to which each telephone set model is > connected to its PBX extension because, theoretically, the telephone might > internally generate higher voltages; or the measured voltages might not > represent the highest possible under certain conditions. >
Hi David: I agree with your assessment of the situation. If you want to keep the SELV interpretation, I think the best solution would be to specify that the series device can only be used with specific digital phones and digital PBXs. Your assertion that the digital phones are SELV devices would have to be based on some analysis of the specific systems, preferably with the cooperation of the manufacturers. This is a lot to ask, but the payoff (in terms of simplifying your design) is significant. I guess you will have to weigh the alternatives. You could certainly design your series device to handle TNV-3 handset cords, but this does not seem very cost effective if the intended use is on digital phones. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
