From: [email protected]@INTERNET on Fri, May 9, 1997 9:48 AM Subject: RE: IEC 950 / UL 1950 creepage and clearance requirements
>You need to be careful when considering the working voltage between TNV and >SELV. For the US, you can use the method outlined by Richard. However, for >Australia and Europe, there is a requirement to isolate the network (TNV) from >protective earth, unless the equipment is professionally installed, or unless >the equipment (and all other equipment plugging into it) does not rely on >protective earthing for safety. This requirement is SUPPLEMENTARY INSULATION >for a PRIMARY CIRCUIT. The WORKING VOLTAGE would then be taken to be 250Vrms >(or is it 230 or 240?) for Europe and Australia, as this is the mains voltage. >This is all outlined in clause 6.3 of EN60950 and AS/NZS 3260. UL 1950 and IEC >950 amd. 4 (which Europe has adopted into EN60950, but I always here >conflicting things on when you can apply amd. 4 to Europe) only require a 1.0kV >barrier from the network to earth. Sweden does not accept this however, even >in amd. 4. In short, if you really want to be international, you will need to >make sure you have a TNV to SELV transformer that provides this supplementary >barrier for a 250Vrms working voltage as this will provide the required barrier >from protective earth to the network. The reasons for this are outlined in >clause 4.4 of EN 41003. (Also, make sure all the creepage distances on your >board comply with this between earth to TNV, and SELV (if your SELV is relying >on protective earth in any way) to TNV. I have a question to ask along these lines. In clause 6.3.3 and Figure 17 the standard refers to components that bridge TNV and Ground. What, if any, are the requirements for capacitors that are used for EMC purposes that bridge TNV and ground above and beyond passing the hipot test as defined in 6.3.3. Dave Clement
