In a message dated 11/27/2001, Jerry Martin writes:
> I'm working on a product that is telecom network powered (-190 Vdc) and will > most likely require a production line hipot test. Being network powered, it > is exposed to outside plant surges and has transient protection designed in > (fuse and sidactor)..... > > Hi Jerry: If the protected circuitry in your product has a permanent connection to earth ground, it may be possible to avoid the production hipot test. For instance, if your telco port was a conventional TNV-1 or TNV-3 interface, there are exemptions available for equipment that has a permanent ground. Unfortunately, the -190 volt power that you mention falls outside of the TNV limits and would normally be classified as a hazardous voltage circuit. USA vendors of T1 equipment with span powering (notably Adtran) have worked with UL to get a special evaluation procedure developed that avoids some of the onerous requirements that would result from classifying the telco port as a hazardous voltage circuit. I do not know if these procedures could be used to provide any relief in your situation. The most straightforward approach for your problem is to simply perform the requested hipot test (with removable links added), but if you really want to avoid this approach there may be a way to use the permanent ground exemptions to eliminate the requirement for having an isolation barrier and performing a hipot test. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
