Humidity matters. Some years back, when doing some experiments around this subject - I too was surprised at just how much voltage different gaps could bear, such that the standard seemed gross overkill. But in a less than purely scientific way, I decided to breath (just breath, not blow) in the vicinity of the withstand, and got different results. It was winter (dry air), and my merely breathing normally - within about a foot of the gap under test - caused a 400V(DC) lower breakdown. I know the standard doesn't hold us to tight humidity spec's, only pollution degree, but maybe the committee that came up with this added enough margin to be sure to always cover such issues.
The geometry of the surface across which the potential is laid matters too (curves, points, parallel planes....), doesn't it. Again, maybe the committee just added guaranteed slop. There is no such thing as too safe. Stephen At 07:39 AM 3/15/2002, MCA Compliance wrote:
Peter I agreee with your comment, but, I have seen lots of boards (material group III) pass high pot tests at 1.5kV with only 2 mm creepage on the boards. yet, 950 specifies 2.5mm for basic insulation. This is why I am after some independent experimental test data correlating creepage and dielectric strength, with different board material properties taken into account. I suppose to flip it around, if a board passes the hi-pot for 1 minute with 2 mm creepage (and the fact that it passes the hi-pot, means the clearance must also have been adequate?), why does 60950 look for 2.5mm creepage ??? rgds Brian -----Original Message----- From: Peter Merguerian [mailto:pmerguer...@itl.co.il] Sent: 15 March 2002 12:00 To: 'MCA Compliance'; Emc-Pstc Post Subject: RE: creepage v breakdown voltage Brian, Your PCB manufacturer should be able to tell you what spacings to keep in order to withstand the test voltages. It all depends on the base material used for the PCB which all have different dielectric strength properties. Remember, the standards reference a minimum creepage distance AND you must still pass the electric strength tests. This e-mail message may contain privileged or confidential information. If you are not the intended recipient, you may not disclose, use, disseminate, distribute, copy or rely upon this message or attachment in any way. If you received this e-mail message in error, please return by forwarding the message and its attachments to the sender. PETER S. MERGUERIAN Technical Director I.T.L. (Product Testing) Ltd. 26 Hacharoshet St., POB 211 Or Yehuda 60251, Israel Tel: + 972-(0)3-5339022 Fax: + 972-(0)3-5339019 Mobile: + 972-(0)54-838175 http://www.itl.co.il http://www.i-spec.com -----Original Message----- From: MCA Compliance [mailto:bally...@iolfree.ie] Sent: Friday, March 15, 2002 11:54 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" ------------------------------------------- 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"
