Thanks Anthony, Doug,
I’d be happy if you could help me further Doug, Now the question is if the peak value of a saw tooth is to be considered a repetitive peak value, while the peak value of a sinus is NOT ! (small difference) (why the distinction otherwise). Second question is of course at what frequency the signal is too slow to be considered a DC voltage where peak equals RMS value. Anthony, I can follow your common sense, and agree with your feelings… However, it’s not the insulation that is determined by the RMS value, that value is indeed based on peak value. The standards CREEPAGE table (PCB or NOT) explicitly mentions to use RMS (or DC) values. So the (air)clearance in my example isi ndeed based on 2 kV as well as distance through insulation) while the creepage over PCB is based on RMS value (with the clearance as a minimum of course). Gert Van: Anthony Thomson [mailto:[email protected]] Verzonden: maandag 12 mei 2014 18:14 Aan: [email protected] Onderwerp: Re: [PSES] Creepage and RMS In the absence of any guidance from standards, perhaps common sense should prevail. The RMS value of an AC voltage (perhaps including a DC components too) represents the equivalent DC voltage that would deliver the equivalent power into a resistive load as the AC voltage. So for current/power based risks such as heating, conductor cross section, contact resistance etc. it would seem acceptable to use the RMS value of an AC voltage. However, for voltage based risks such as arcing, insulation breakdown, component failure, etc., it would seem sensible to consider the peak voltages. Taking Gert’s example of a 2 kV, 3 Hz sawtooth voltage waveform. The RMS voltage is 2000/sqrt(3)=1155 Vrms. If this were being fed into a 50 ohm load (say) then conductors of a safe current carrying capacity of 1155/50=23A (CD) should be OK. I’m not sure though that I’d be happy handling those cables with an insulation breakdown of 1200 V, or even 1500V. I’d expect that to be in excess of the 2000V peak value. Just my thoughts. T ----- Original Message ----- From: ce-test, qualified testing bv - Gert Gremmen Sent: 05/12/14 03:20 PM To: [email protected] 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 P Before printing, think about the environment. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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To post a message to the list, send your e-mail to <[email protected]> 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) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- 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 <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
