Try this. For flat electrodes, at sea level, and normal temperatures; eliminating such factors as humidity, dust, illumination, and the electrode materials; the molecules of the gases that compose common air, get ionized in the presence of an electric field of about 30KV/cm.
So, since - electrode shape, barometric pressure, temperature, humidity, dust, presence of photons, and composition of the materials and shape of the electrodes, as well as the composition of the 'air' (gases), and also any other local (competing) electromagnetic fields - can all affect the definitive voltage that will jump a given gap - is it any wonder that the standard includes what otherwise appears to be a lot of slop. Stephen At 09:28 AM 3/15/2002, Roman, Dan wrote:
I was looking into this a few weeks ago also and found similar results experimentally as other posters have mentioned. The only voltage per inch spec I was able to come up with was in the IPC specs but they were way out of whack! 0.12 mils per volt or more meaning that 2121 Vdc distance that the safety standards say should be 2.5 mm the IPC spec is saying you need 5 mm!!!! While the safety standards may be conservative to allow for temperature, grease, dirt, etc. over time the IPC specs are ultra-conservative. The dielectric tables for hermetically sealed material group III is probably closer to the actual breakdown but I never did find a spec I could use to predict the ACTUAL breakdown voltage of a gap between traces. If anyone finds a rule of thumb or equation I'd like to have it also. Dan -----Original Message----- From: MCA Compliance [mailto:bally...@iolfree.ie] Sent: Friday, March 15, 2002 4:54 AM To: Emc-Pstc Post Subject: creepage v breakdown voltage does data exist which correlates creepage distance on a pcb with hi-potential test voltage it should withstand ? for example, I know 60950 sugests a test voltage of 1500Vrms for 1 minute and a creepage of 2.5mm (material group III) for basic insulation. How did they arrive at 2.5 mm ??? Brian email: i...@mcac.ie ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
