Dear Edward and Moshe, The EN60950 standard allows you various options for compliance with insulation between the max 72 Vdc source of supply (considered a hazardous secondary circuit) and SELV.
One way to comply is reinfoced insulation as Edward has stated. But based on the many products which we have tested in our labs, we find that this providing reinforced insulation is not a practical solution for most clients. In many cases, our clients do not have insulation at all. In this case, the standard allows you to interconnect hazardous secondary circuits and SELV if abnormals are done (shorting or opening of components or circuits) to detrmine that the SELV limits are not exceeded. Remember that for some countries (Australia and Germany), CO's recognize the max 72 Vdc supply as a TNV-2 circuit. As such for these countries where the CO supply voltage can reach up to 72 Vdc, you may wish to comply with the TNV-2 to SELV limits specified in my previous e-mail. For most other countries, the CO supply voltage is earthed SELV and does not exceed 60 Vdc. For these countries you may wish to comply with the SELV to SELV or operational insulation requirements. Regards, Date sent: Thu, 22 Oct 1998 14:47:40 -0400 From: Edward Eszlari <[email protected]> Subject: RE: isolation of battery (72V max) input To: "INTERNET:[email protected]" <[email protected]>, [email protected], [email protected] Send reply to: Edward Eszlari <[email protected]> > Moshe, > > The answer to your question is Reinforced insulation for the working > voltage measured in that location. > > The 72V supply is considered hazardous voltage and if an SELV circuit is > present on conductors nearby, this is the type of insulation system that is > required. If this "CO like" enviroment can be considered a "Restricted > Access Area" per 2.1.4.2 (EN60950), or "Service Access Area" per 2.1.4.1, > lesser requirements may apply. Also consider if this "SELV" circuit does > not need to be classified as SELV (no operator access), you may be able to > get away with no insulation, but other requirements may apply depending on > how this system is set-up. > > Regards, > > > Edward Eszlari > TUV Rheinland of N.A., Inc. > Marlborough, MA > 508-460-0792 > > > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
