Hi James:
My answers to your questions: 1. Does 6.7.3 apply for the clearance between the secondary winding and earth as indicated? Yes. 2. If NO to 1) then what parts should this insulation be between? 3. If YES to 1) then: a. what is the safety hazard that is being addressed by applying Basic insulation values from Table 6 here? The standard's assumption is that transient voltages do appear in secondary circuits. See NOTE following 6.7.3.1. A transient voltage can cause a clearance or creepage to fail. Solid insulation is required to have suitable electric strength to withstand the transient voltage. b. Why isn't this shown on Figure D.1e) as being required? I assume that the figures are either insulation in general, including clearances (air insulation) or just for solid insulation. 4. If the working voltage between terminals X and Y in the sketch is less than the Hazardous Live thresholds in 6.3.1 then it is be permitted to be present on an Acccessible external terminal, correct? Yes. 5. Earthing either end of this winding will make 6.7.3 redundant, correct? I wouldn't describe the requirement as "redundant." If one end of the winding is connected to earth, then clearly the clearance and creepage requirements do not apply to that one terminal. However, the other terminal still must meet the clearance and creepage requirement. The standard seems not clear as to whether clearance (air insulation) is considered as insulation or a separate parameter. Note that the values for creepage distance are based on rated voltage, not transient voltage. This is because failure of a creepage is caused by a long-term voltage. However, physically, a creepage cannot be less than a clearance. Good luck, Rich - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
