Hello again. The following is food for thought that came to light during a recent project development meeting. I invite your comments and anecdotes on the following.
My earlier post regarding test probe 11 of IEC 61032 was related to comparing force test methods to deflect enclosures to reduce effective clearances that provide (at least) reinforced insulation. The standards are IEC 60950-1:2005 and IEC 60065:1998 (I don't have a copy of the 2001 version). In 60950-1, the method is to apply a force of 250 N using a 30 mm diameter circular plane surface. This corresponds to a pressure of 0.35 N/mm². In 60065, the method is to apply a 30 N force using test probe 11 of IEC 61032 (which bears a significant resemblance to probe in 60950-1, Figure 2A and, for the purposes of this discussion, treated as dimensionally identical at the tip). To calculate a pressure, a little cheating** is needed. For the purposes of this discussion, I've assumed that the contact area corresponds approximately to cross-section B-B in 60950-1, Figure 2A, and further approximated by a rectangle (not particularly realistic, but close enough for this discussion)). This corresponds to a pressure of ~33 N/mm². 60950-1, §2.10.3.1, first dashed paragraph, the minimum clearance is 10 mm. 60065, Figure 9, assuming the peak voltages involved are between 354 V and 900 V, the minimum clearance is 6 mm. Looking only at the forces involved and a design cramped for space, 6 mm is far more attractive than the 167% larger 10 mm. Looking only at the forces involved, it's easy to expect that the 250 N test is more severe. But, since materials respond to applied pressures resulting >from applied forces (an 'other things being equal' statement that ignores quite a few 'other' things), the 30 N test looks more severe by nearly two orders of magnitude. 60065, while easier on the volumetric real estate budget, requires some good basic reinforcement applied to the mechanical design in the relevant areas. 60950-1, while easier on the other mechanical design features needed, requires a sacrifice of volumetric real estate. ** Approximately calculation of the area of cross-section B-B: Side A = 2×(2 mm)×[sin(37°/2)] = 0.93 mm Side B = 2×(4 mm)×[sin(14°/2)] = 0.97 mm Area = 0.9 mm² Regards, Peter L. Tarver, PE ptar...@ieee.org CONFIDENTIALITY This e-mail message and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail message, you are hereby notified that any dissemination, distribution or copying of this e-mail message, and any attachments thereto, is strictly prohibited. If you have received this e-mail message in error, please immediately notify the sender and permanently delete the original and any copies of this email and any prints thereof. ABSENT AN EXPRESS STATEMENT TO THE CONTRARY HEREINABOVE, THIS E-MAIL IS NOT INTENDED AS A SUBSTITUTE FOR A WRITING. Notwithstanding the Uniform Electronic Transactions Act or the applicability of any other law of similar substance and effect, absent an express statement to the contrary hereinabove, this e-mail message its contents, and any attachments hereto are not intended to represent an offer or acceptance to enter into a contract and are not otherwise intended to bind the sender, Sanmina-SCI Corporation (or any of its subsidiaries), or any other person or entity. - 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 emc-p...@ieee.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...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
