Ron, I have conducted hundreds of leakage current tests but never personally redesigned a product to reduce leakage, so here is my "no previous experience" input: My guess is that your leakage current is predominantly line frequency (you may wish to confirm by looking at the leakage current frequency composition). I also guess that the switching power supplies have additional filtering in the front end with capacitors to ground (in addition to the 2 separate filters). This is making for a lot of capacitance to ground which is the source of your leakage current. If these assumptions are correct, the only way to reduce leakage current would be to reduce capacitance to ground (do you really need all those filters). Or, isolate everything behind an isolation transformer (i.e. the medical way). If my presumption that filter capacitance is the cause is correct, it would be additive.
Regards, Bill Bisenius, N.C.E. E.D.& D. www.productsafeT.com From: Ronald R. Wellman [mailto:[email protected]] Sent: Wednesday, November 17, 2004 8:26 AM To: EMC-PSTC List Subject: Multiple Leakage/Touch Current Sources Howdy all, I have come across a problem where a product is exceeding 3.5 ma of touch current. The product in question has 2 line filters and 4 Switching Mode Power Supplies. Because of the addition of the fourth power supply the overall touch current can be as much as 4.0 ma. Ideally, we do not want to make the product so it has to be hard-wired to the building mains. Because of the high touch current, does anyone know what the relationships are between different touch current sources? I've heard that touch current is not linear when you add up the different sources and phase shifts between L-G and N-G might be a problem. However, I'm looking for some detailed information on this issue so I can provide ways to investigate the problem and hopefully reduce the overall touch current. BTW, the product is not medical equipment and all touch current tests are done with the product operating at 264 V AC, 50 Hz. Best regards, Ron Wellman ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
