Dear Rich, Input voltage above 60Vdc can be treated as TNV-2 circuit and according to the standard, it is enough to have basic insulation input to output, however, fault condition tests still need to be conducted.
So basic + supplementary is not always required if input is >60VDC. Best regards, Boštjan Glavič On 21. jan. 2015, at 21:04, "Richard Nute" <[email protected]<mailto:[email protected]>> wrote: Dear Boštjan: Page 7 is mostly wrong. Comments in blue. Best regards, Rich DC/DC converter isolation requirements Functional insulation between the DC/DC converter’s input and output is allowed if: > The AC/DC power supply has reinforced or double insulation between the AC line supply and its DC output. ... if the output is less than 60 volts d.c. (The DC/DC converter must pass fault condition testing and withstand an electrical strength test for basic insulation if its normal input voltage exceeds 60 VDC.) Well… no electric strength is specified for a secondary circuit to a secondary circuit. No transients get through the AC/DC power supply; if they did, the secondary semiconductors would be damaged or destroyed. If the input voltage exceeds 60 volts d.c., then the input to output insulation must be comprised of basic plus supplementary (double). Or, basic plus grounding circuit sufficiently robust to carry the input d.c. fault current. > The AC/DC power supply has basic or supplementary insulation between the AC line supply and its DC output, and the output of the DC/DC converter connects to protective Earth. (Again, the DC/DC converter must pass fault condition testing and withstand an electrical strength test for basic insulation if its normal input voltage exceeds 60 VDC.) The AC/DC power supply cannot have supplementary insulation alone. Supplementary insulation is supplementary to basic insulation. For any voltage greater than 42.4 volts peak or 60 volts d.c., the input to output insulation must be comprised of basic plus supplementary (double). Or, basic plus grounding circuit sufficiently robust to carry the input a.c. and d.c. fault current. Alternatively, the converter can be subjected (in its application) to input-to-output fault tests, where the output is to remain less than 42.4 volts peak or 60 volts d.c. > The AC/DC power supply has basic or supplementary insulation between the AC line supply and its DC output, and the input of the DC/DC converter connects to protective Earth. (In this case, the normal input voltage must not exceed 60 VDC.) The AC/DC power supply cannot have supplementary insulation alone. Supplementary insulation is supplementary to basic insulation. The d.c. grounding circuit (output of the AC/DC power supply) must be sufficiently robust to carry the input a.c. fault current. In summary, this means that functional insulation is adequate for the DC/DC converter in almost all practical system implementations. If the converter’s normal input voltage exceeds 60 VDC, it must additionally withstand an electrical strength test for basic insulation and pass fault condition testing. Assuming the DC/DC converter input is SELV, then I agree with the first sentence. I disagree with the second sentence; see previous comments regarding isolation requirements. As Boštjan has pointed out, if the DC/DC converter creates voltages exceeding the limits of SELV, then fault-condition tests from the non-SELV to the output must be done. Chances are, such tests will cause the inverter circuit to stop, and the output will be zero (SELV) or the input D.C. - ---------------------------------------------------------------- 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 <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. 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: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
