I knew I shouldn't have commented on this subject !! We perform the IEC 60950 grounding test by connecting our 25A source between the ground pin of the mains cord and the metalwork we want to check - and measure the volt drop between the two points. If the surface was painted, we might have to "dig" through the coating with our test probe. Basically, our products consist of many steel parts all screwed together, most of them plated, but some of them painted. Where we have an ac operated module within our products, such as a printer, monitor, or power supply, invariably with a plated chassis, (screwed down with the afore-mentioned screws), we supply it from a 3 core cord, but if we removed the ground wire from this cord (which would run back to an ac distribution circuit), there is no noticeable difference in the results we get.
Regards, John Crabb, Development Excellence (Product Safety) , NCR Financial Solutions Group Ltd., Discovery Centre, 3 Fulton Road, Dundee, Scotland, DD2 4SW E-Mail :john.cr...@scotland.ncr.com Tel: +44 (0)1382-592289 (direct ). Fax +44 (0)1382-622243. -----Original Message----- From: Ron Pickard [mailto:rpick...@hypercom.com] Sent: 25 March 2002 15:28 To: Crabb, John Cc: emc-p...@ieee.org Subject: RE: chassis bonding - star washers enough? Hi John, You wrote: >We use screws which have combined hex/posidriv heads with >serrations under the head, which eliminates the need for star washers. >We find these work very well for zinc plated parts. On epoxy painted >parts, they also seem to cut thru the paint and give a satisfactory >result - you might feel "happier" if you have more than one screw >for any given part. Using these screw types may be "satisfactory" at the time of production, but what will be expected when the product is placed into service and into varying environments? Will the newly exposed chassis surfaces (I agree that they would very small) become so oxidized that the oxidation leaches to the "satisfactory" ground connection? Probably not, but IMHO, due diligence might prescribe an evaluation. >We also use self-clinching PEM nuts with good results. >Typically we find that where a grounding conductor has been >brought to a particular area of our products, we would still >pass the 0.1 ohm, 25A test when we remove the conductor. May I ask how you pass this test when, as you stated, the conductor is removed (just curious). Please provide clarification. Best regards, Ron Pickard rpick...@hypercom.com ------------------------------------------- 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"
