Hello group, My company manufactures high energy power conversion equipment and we often deal with insulation between mains voltages and SELV as well as high voltage outputs and SELV. During part of our type testing we simulate single fault conditions such as a breakdown of basic or supplemental insulation. Some standards explicitly allow a short term rise in voltage on the SELV circuit during this test. My understanding is that this voltage rise should be confined to a very small part of the circuit and limited in time. These areas are not operator-accessible and the voltage would not be allowed to propagate throughout the rest of the SELV system.
1) In IEC60950:1999 sec. 2.2.3 indicates that under single fault conditions, SELV circuits may see a 71V peak or 120V DC for up to 0.2 seconds. Paragraph 3 of that clause also speaks to SELV circuits that are NOT operator-accessible, i.e. internal SELV circuits. Does this section mean to say that the voltage on "internal SELV" may in fact go higher than the 71V Peak and 120 V DC for a short time? Naturally, I would never allow the operator-accessible areas to exceed the levels of sec. 2.2.3. 2) IEC60950:1999 also has similar information for TNV circuits or products. I have always assumed that TNV is for telecommunications products only, but the definition in sec. 1.2.8.9 does not actually say this. Additionally 1.2.8.10 - 1.2.8.12 describe the various types of TNV, but it appears that TNV-2 does not specifically exclude our non-telecom products. My concern is that this might possibly open up section 2.3 for our power conversion products. Is someone able to give me a clear definition of TNV and what the acronym means? The standard seems a little ambiguous in my mind. 3) EN 61010-1:1993 sec. 6.3.2 and fig. 1 also address temporary voltages on accessible circuits. The figure allows certain time-voltage levels during a single fault condition. Does the term "accessible" mean the same as IEC 60950 "operator-accessible" and allow for higher voltages to occur on internal SELV circuits that are not operator-accessible? 4) EN50178:1997 sec. 5.2.8.4 seems to make this allowance by saying in paragraph 2 that in a single fault test the voltage at the output terminals cannot exceed the SELV voltages of 25 Vac or 60 Vdc. Apparently EN50178 does not allow for a short term voltage rise in internal SELV circuits, is this actually true or false? Thank you for any help you can provide. Best regards, -doug ================================= Douglas E. Powell Regulatory Compliance Engineer Advanced Energy Industries, Inc. 1625 Sharp Point Dr. Ft. Collins, Co 80525 mailto:[email protected] http:\\www.advanced-energy.com\ ================================= ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
