The issue with some 60664 tables is that it is (for 0 to 2km) based on Paschen's Law, which is for a simple homogenous e-field. So creepage via RMS is an incomplete analysis.
As others have stated, spacing should be determined by both peak and RMS. And because too many do not measure WV correctly, I strongly suggest reading papers and articles by P. Perkins and R. Nute on this subject, and ”The physical fundamentals of low-voltage insulation co-ordination” by Klaus Stimper. In a very nutty shell, you need to determine the following for the intended end-use environment: - OV category - CTI of materials - pollution degree - atmospheric chemistry - frequency-based di-electric heating - WV for the complete range of rated operating conditions Have rejected more than one component mfr's CB reports due to incorrect interpretations of IEC60664 and calculations of 'RMS' (am looking at you people in NRTLs/SCCs/NBs). Finally, the OP indicated that "Creepage is based on the RMS value of the voltage so is based on 1120 V", which indicates a reference a particular safety standard. What does that standard say about WV measurements for the determination of spacing and test voltages ? Brian ----- Original Message ----- From: ce-test, qualified testing bv - Gert Gremmen Sent: 05/12/14 03:20 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] Creepage and RMS I have a question on creepage distances. A product creates a saw tooth High voltage of 2000 Vpeak The VRMS measured on the scope on a full period equals 1120 V Creepage is based on the RMS value of the voltage so is based on 1120 V. Now the frequency of the sawtooth is 3 Hz. Should I still consider the RMS value, and at what frequency should I consider this as a DC value in regard to creepage.... Anyone aware of the IEC 60664 standard in respect to low frequency signals ?? Regards, Ing. Gert Gremmen, BSc - ---------------------------------------------------------------- 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://www.ieee-pses.org/list.html (including how to unsubscribe) 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>
