In a message dated 5/23/01, David Gelfand writes:
> We are in the preliminary design stage for a new voice-band telephone > interface. Is this current limiting requirement still mandatory? Hi David: The 60 mA current limiter is no longer mandatory in Europe. Prior to Europe's harmonization efforts, there was a 60 mA current limiter requirement in France under their national standard B1123A. When CTR 21 was created under the second phase telecom directive to replace all of the EU national standards, the 60 mA current limiter requirement (modified in ways that made it more difficult than France's national requirement) was included in CTR 21. When the new RTTE directive 99/5/EC became effective in April last year, CTR 21 ceased to be a regulatory requirement for CE marking. Under the RTTE directive that is now in effect, the only requirements that a PSTN interface must meet for CE marking are those for safety and EMC. There are no longer any regulatory requirements that specify parameters such as the DC V-I characteristic for CE marking in Europe. The only caveat is that according to France Telecom, there are still some PSTN lines in France that will not function properly if the TE does not incorporate the 60 mA limiter. They are working to eliminate these lines, but they claim it will take them until October 2002 to complete the transition. To address this problem, the European Commission has ruled that non-current limited equipment sold in France must be accompanied by a warning that it should only be used on PSTN lines that do not require current limiting. In my view, there are only three reasons why any sane person would include the current limiter in a new design: 1) They plan to sell a lot of product in France between now and October 2002. 2) They have a European customer that wants them to be "CTR 21 compliant" since that is the closest thing available to a standard PSTN specification for Europe. 3) They want to take advantage of the fact that a few non-EU countries, such as the Czech Republic, will accept CTR 21 compliance as an alternative to their national specifications. If your intended application does not meet any of the above criteria, I would recommend leaving the current limiter out. It certainly simplifies the design, and it allows you to cover more countries (such as Japan and Singapore) without having to switch the current limiter out. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
