Alternately, a test with a DC voltage of the peak value of the corresponding
AC voltage will help you draw the right conclusion. Not all standards allow the replacement of AC by DC tests, however. Most standards do allow the removal of phase-ground components (if certified) such as varistors and capacitors (emc filters) before carrying out the test. This is not very feasible during production tests, however. Regards, Ing. Gert Gremmen ce-test, qualified testing bv Van: emc-p...@ieee.org [mailto:emc-p...@ieee.org] Namens John Allen Verzonden: Thursday, November 13, 2008 10:20 PM Aan: 'Ted Eckert'; 'Robert F. Keller'; EMC-PSTC@LISTSERV.IEEE.ORG Onderwerp: RE: Current limit for Dielectric Test Hi Folks >From experience, I agree with what Ted says - especially w.r.t. his last paragraph about setting a LOWER limit. Failure to exceed the lower limit could also indicate a faulty EMI filter with capacitors of lower values than specification - thus meaning you may have an emissions issue with the units in question. I used to sample a batch of a dozen or so units for each type of unit, and then set higher and lower limits for the test personnel to check. Regards John Allen -----Original Message----- From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Ted Eckert Sent: 13 November 2008 16:51 To: Robert F. Keller; EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: Current limit for Dielectric Test Hello Rob, There is no current limit specified, and there is no way a limit could be specified. Take a look at IEC 60950-1 section 5.1.7. You will see that there are types of equipment where the touch current is allowed to exceed 3.5 mA. This is typically equipment that is field wired or at least has an industrial locking plug. The high touch current is often due to a significant amount of filtering in the power supply including Y-capacitors. If these capacitors (and other circuits bridging primary to ground) are allowing over 3.5 mA at the normal operating voltage, they will pass far more current at the voltages used for the electric strength test. I have worked with high power telecommunication rectifiers that have a lot of filtering on their input. They have a very high touch current, but they are field wired and have a solid ground connection. The risk to the user from the touch current is quite low. The amount of current that flows during the electric strength test is quite high. You should know what the expected current will be during the electric strength test. You can calculate it from the test voltage and the impedance of the circuits between primary and ground. Giving some safety margin to this value, you can generally select a reasonable starting point for the upper limit on your testing. As the standard notes, a failure is a dramatic increase in current, not a constant high current. You need to know your equipment to determine the proper test limits. Many types of electric strength testers will also let you set a lower limit for failure. This too should be set properly. If the current during the electric strength test is too low, you may have a bad test setup or a bad connection in your product. Ted Eckert Compliance Engineer Microsoft Corporation ted.eck...@microsoft.com The opinions expressed are my own and do not necessarily reflect those of my employer. From: Robert F. Keller [mailto:r...@cclab.com] Sent: Thursday, November 13, 2008 8:36 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Current limit for Dielectric Test Hello Group, I have a question regarding the Electric Strength test in 60950-1 section 5.2. It says in that section that you have a failure or the insulation broke down when the current which flows as a result of the application of the test voltage rapidly increases in an uncontrolled manner. So, is there an exact current limit at which it is considered to have "shorted"? And if so, is this printed in any standard? Any insight in this would be greatly appreciated. Best Regards, Rob Keller Senior Engineer Communication Certification Laboratory Ph.: 801.972.6146 Ext.237 Fax: 801-972-8432 r...@cclab.com - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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