Dear all, Thank you for your comments.
The below mentioned construction was rejected. The client needs to use high breaking fuse and not enhanced fuse. The problem is that in every switch mode power supply you can get high short circuit current which is causing non-high breaking fuse to burst (there is a resistance <1ohm even with power supply cord). This happens during fault condition testing in primary circuit right after the fuse (e.g. across the varistor or diode bridge). But test has to be performed on the correct branch circuit and in peak of input voltage. But the problem is that standard does not define precisely how to conduct the abnormal condition (e.g. IEC 60950-1). There are many power supplies on the market with low breaking or enhanced breaking type of fuse and they are approved by different certification bodies. Some power supplies have only TR5 low breaking fuse. That's why I decided to ask you experts for 2nd opinion. UL has a PAG about this issue and does not allow it. However in the past many such construction were acceptable also by UL. Best regards, Boštjan Glavič Head of Laboratory, Laboratory of Electronic Engineering www.siq.si SIQ Ljubljana, Trzaska c. 2, SI-1000 Ljubljana, Slovenia, VAT ID: SI23509678 t +386 (0)1 4778 265, m +386 (0)41 391 283, f +386 (0)1 4778 444 -----Original Message----- From: Pete Perkins [mailto:peperkin...@cs.com] Sent: Wednesday, August 07, 2013 11:33 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Cc: Boštjan Glavič Subject: RE: [PSES] breakage of the fuse Bostjan commented: During the abnormal tests in primary circuit, internal input fuse operates and glass breaks. However, fuse is inside the tubing and broken glass does not spread around. Would you accept such construction? - - - - - Bostjan, Such a question can have several answers, among other things it depends upon who the 'you' is. If the 'you' is a party who suffered personal injury or financial damage they probably wouldn't be willing to accept such construction & you will hear from them. If the 'you' is a test house or regulator they probably would be looking closely for a way to not accept such construction. If the 'you' is a tinkerer who likes to solve difficult problems they probably would accept such construction & be happy that they could fix it and get on with using the product. Perhaps the question you should ask is 'would your mother accept such construction?' or would she be all over you because of what happened. Would the general public know how to clear out the mess in the fuseholder and insert a new fuse to get back in operation? Think about it; not all questions have one simple answer. :>) br, Pete Peter E Perkins, PE Principal Product Safety Engineer PO Box 23427 Tigard, ORe 97281-3427 503/452-1201 fone/fax p.perk...@ieee.org - ---------------------------------------------------------------- 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://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
