Re: [PSES] SELV rated power supplies
Dear Boštjan: You said: 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. A TNV-2 circuit can be up to 71 volts peak or 120 volts d.c., but it cannot be accessible (to an ordinary person) or connected to a SELV circuit. The separation requirements between TNV-2 and SELV/accessible parts is basic insulation and, if necessary, fault tests. If a dc/dc converter generates greater than SELV in its operation but less than 71 volts peak or 120 volts d.c., I suppose the circuit can be classed as TNV-2, although this seems strange to me. Same for 71 volts peak or 120 volts d.c supply circuit to the converter. (If the output remains SELV during and after a fault test of basic insulation, the test proves that the basic insulation is not necessary; this is a flaw in the standard.) Best regards, 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] SELV rated power supplies
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" mailto:ri...@ieee.org>> 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] SELV rated power supplies
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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] SELV rated power supplies
Dear all, Please check below link. I must say I do not agree with last paragraph on page 7, since they do not consider internally generated high voltages. Even the input is SELV, internally there might he high voltages generated and therefore by having only functional insulation in-out, fault conditions are required in order to verify that output remains SELV. http://archive.ericsson.net/service/internet/picov/get?DocNo=31/28701-FGB101378&Lang=EN&HighestFree=Y Boštjan Glavič On 20. jan. 2015, at 20:05, "Scott Aldous" <0220f70c299a-dmarc-requ...@ieee.org<mailto:0220f70c299a-dmarc-requ...@ieee.org>> wrote: For the power supplies that are certified by UL under category code QQGQ2, UL does have a standardized table format on their online cert directory that includes a code they call the Output Category. The intent is to identify those supplies that have been evaluated for SELV output, or other types of output. More information can be found in the guide card for that category: http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/showpage.html?name=QQGQ2.GuideInfo&ccnshorttitle=Power+Supplies,+Information+Technology+Equipment+Including+Electrical+Business+Equipment+-+Component&objid=1073787375&cfgid=1073741824&version=versionless&parent_id=1073787374&sequence=1 On Tue, Jan 20, 2015 at 10:17 AM, Brian Oconnell mailto:oconne...@tamuracorp.com>> wrote: Mr. Nute’s response is significant and is worthy of re-emphasis. And Mr. Woodgate answered this same question to Mr. Nyffenegger previously: " The power supply as a whole cannot claim that unless ALL its outputs meet the SELV requirements. But it does meet the requirements for safety isolation, so those outputs that meet the voltage requirements are SELV." SELV, TNVx, LPS, LCC, etc are specific ratings that would be indicated in the Conditions of Acceptability in both the test certification document required to bear a CAB’s logo and the respective CB report. And as many power supplies are components, the report will be necessarily incomplete; and only the assessment in the end-use construction can provide a complete report. Per Mr. Nute, other than simple flyback converters, most component SMPS are too complex to be evaluated by other than an assessment directed by the original manufacturer (in last 15 years, have encountered only three agency engineers capable of a complete and independent assessment of SMPS). There is never any logical reason to assume a ‘certified’ component power supply will meet any specific ratings unless stated in a CAB’s report. Brian -Original Message- From: Richard Nute [mailto:ri...@ieee.org<mailto:ri...@ieee.org>] Sent: Monday, January 19, 2015 12:55 PM To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] SELV rated power supplies Hi Dave: EN60950-1 is not equal to SELV. Certifications and reports do not necessarily indicate outputs are SELV, although careful reading of the test results can conclude that the outputs are SELV or not. Not all outputs of EN60950-1 power supplies are SELV and need not be. The power supplies are nevertheless EN60950-1 power supplies. The requirement for SELV is whether or not the circuit is accessible. Accessible circuits must be SELV. To perform a single-fault test, one must understand how the circuits operate, and what faults could cause the output to possibly exceed SELV limits. In today's power supply topology, such circuit analysis is not necessarily straight-forward. Your statement "Therefore my contention is it cannot be assumed that a power supply listed as EN 60950-1 compliant on a manufacturer's data sheet is also SELV compliant unless explicitly stated so or proven in the test report results." is correct. Best regards, 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<mailto:emc-p...@ieee.org>> 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)<http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org<mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@iee
Re: [PSES] SELV rated power supplies
For the power supplies that are certified by UL under category code QQGQ2, UL does have a standardized table format on their online cert directory that includes a code they call the Output Category. The intent is to identify those supplies that have been evaluated for SELV output, or other types of output. More information can be found in the guide card for that category: http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/showpage.html?name=QQGQ2.GuideInfo&ccnshorttitle=Power+Supplies,+Information+Technology+Equipment+Including+Electrical+Business+Equipment+-+Component&objid=1073787375&cfgid=1073741824&version=versionless&parent_id=1073787374&sequence=1 On Tue, Jan 20, 2015 at 10:17 AM, Brian Oconnell wrote: > Mr. Nute’s response is significant and is worthy of re-emphasis. > > > > And Mr. Woodgate answered this same question to Mr. Nyffenegger previously: > > > > " The power supply as a whole cannot claim that unless ALL its outputs > > meet the SELV requirements. But it does meet the requirements for safety > > isolation, so those outputs that meet the voltage requirements are SELV." > > > > SELV, TNVx, LPS, LCC, etc are *specific ratings* that would be indicated > in the Conditions of Acceptability in both the test certification document > required to bear a CAB’s logo and the respective CB report. And as many > power supplies are *components, *the report will be necessarily > incomplete; and only the assessment in the end-use construction can provide > a complete report. > > > > Per Mr. Nute, other than simple flyback converters, most component SMPS > are too complex to be evaluated by other than an assessment directed by the > original manufacturer (in last 15 years, have encountered only three agency > engineers capable of a complete and independent assessment of SMPS). There > is never any logical reason to assume a ‘certified’ component power supply > will meet any specific ratings unless stated in a CAB’s report. > > > > Brian > > > > -Original Message----- > From: Richard Nute [mailto:ri...@ieee.org] > Sent: Monday, January 19, 2015 12:55 PM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] SELV rated power supplies > > > > Hi Dave: > > > > EN60950-1 is not equal to SELV. > > > > Certifications and reports do not necessarily > > indicate outputs are SELV, although careful > > reading of the test results can conclude that the > > outputs are SELV or not. > > > > Not all outputs of EN60950-1 power supplies are > > SELV and need not be. The power supplies are > > nevertheless EN60950-1 power supplies. > > > > The requirement for SELV is whether or not the > > circuit is accessible. Accessible circuits must > > be SELV. > > > > To perform a single-fault test, one must > > understand how the circuits operate, and what > > faults could cause the output to possibly exceed > > SELV limits. In today's power supply topology, > > such circuit analysis is not necessarily > > straight-forward. > > > > Your statement > > > > "Therefore my contention is it cannot be assumed > > that a power supply listed as EN 60950-1 compliant > > on a manufacturer's data sheet is also SELV > > compliant unless explicitly stated so or proven in > > the test report results." > > > > is correct. > > > > Best regards, > > 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 > > 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) <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <dhe...@gmail.com> > -- Scott Aldous Compliance Engineer Google 650-253-1994 scottald...@google.com - This message is from the IEEE Product Safety E
Re: [PSES] SELV rated power supplies
Mr. Nute's response is significant and is worthy of re-emphasis. And Mr. Woodgate answered this same question to Mr. Nyffenegger previously: " The power supply as a whole cannot claim that unless ALL its outputs meet the SELV requirements. But it does meet the requirements for safety isolation, so those outputs that meet the voltage requirements are SELV." SELV, TNVx, LPS, LCC, etc are specific ratings that would be indicated in the Conditions of Acceptability in both the test certification document required to bear a CAB's logo and the respective CB report. And as many power supplies are components, the report will be necessarily incomplete; and only the assessment in the end-use construction can provide a complete report. Per Mr. Nute, other than simple flyback converters, most component SMPS are too complex to be evaluated by other than an assessment directed by the original manufacturer (in last 15 years, have encountered only three agency engineers capable of a complete and independent assessment of SMPS). There is never any logical reason to assume a 'certified' component power supply will meet any specific ratings unless stated in a CAB's report. Brian -Original Message- From: Richard Nute [mailto:ri...@ieee.org] Sent: Monday, January 19, 2015 12:55 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] SELV rated power supplies Hi Dave: EN60950-1 is not equal to SELV. Certifications and reports do not necessarily indicate outputs are SELV, although careful reading of the test results can conclude that the outputs are SELV or not. Not all outputs of EN60950-1 power supplies are SELV and need not be. The power supplies are nevertheless EN60950-1 power supplies. The requirement for SELV is whether or not the circuit is accessible. Accessible circuits must be SELV. To perform a single-fault test, one must understand how the circuits operate, and what faults could cause the output to possibly exceed SELV limits. In today's power supply topology, such circuit analysis is not necessarily straight-forward. Your statement "Therefore my contention is it cannot be assumed that a power supply listed as EN 60950-1 compliant on a manufacturer's data sheet is also SELV compliant unless explicitly stated so or proven in the test report results." is correct. Best regards, 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] SELV rated power supplies
Hi Dave: EN60950-1 is not equal to SELV. Certifications and reports do not necessarily indicate outputs are SELV, although careful reading of the test results can conclude that the outputs are SELV or not. Not all outputs of EN60950-1 power supplies are SELV and need not be. The power supplies are nevertheless EN60950-1 power supplies. The requirement for SELV is whether or not the circuit is accessible. Accessible circuits must be SELV. To perform a single-fault test, one must understand how the circuits operate, and what faults could cause the output to possibly exceed SELV limits. In today's power supply topology, such circuit analysis is not necessarily straight-forward. Your statement "Therefore my contention is it cannot be assumed that a power supply listed as EN 60950-1 compliant on a manufacturer's data sheet is also SELV compliant unless explicitly stated so or proven in the test report results." is correct. Best regards, 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
[PSES] SELV rated power supplies
Folks, EN 60950-1 defines the requirements for SELV as well as many other requirements.SELV is required under certain conditions as defined and where it's not required it's not needed. EN 60950-1 does not state that all control circuits must be SELV. Therefore all control circuits need not be SELV and it cannot be assumed that all control voltages in an EN 60950-1 machine are SELV. DC power supply manufacturers routinely certify and claim compliance to EN 60950-1. However, I have only seen a few power supply data sheets explicitly claiming SELV compliance. In fact, I have reviewed several EN 60950-1 test reports for various power supplies (not claiming SELV compliance) and the test results for the SELV clauses are week or actually show non-compliance. For example, component single fault testing for over voltage was insufficient. In some cases power supplies rated for nominal voltage meeting SELV requirements (for example 48VDC) could be adjusted for an output above SELV ratings or the fault testing generated output voltages above SELV requirements (60VDC for longer than 200 ms). In some cases the power supply data sheets will even list EN 60950-1 compliance for supplies with a rated output voltage range above SELV, for example 45-62 VDC. Therefore my contention is it cannot be assumed that a power supply listed as EN 60950-1 compliant on a manu! facturer's data sheet is also SELV compliant unless explicitly stated so or proven in the test report results. I have run across many folks and some CE Machinery Directive compliance reports stating/assuming SELV compliance strictly due to power supplies being certified to EN 60950-1 (without any specific SELV claim). In other words EN 60950-1 == SELV. I'm wondering what other folks opinions are on this? Does anyone know of any supporting articles/guidelines etc. clarifying this? David P. Nyffenegger, PMP, SM-IEEE Product Development Manager - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
