RE: chassis bonding - star washers enough?
We are users of many types of electro-medical equipment, all of which we subject to basic safety testing before placing into service in our hospital. Our experience is that metal-to-metal is the only relaible means of chassis earth-bonding. We regularly find that equipment delivered to us which has relied upon star-washers or other types of fastening to cut through surface coatings to achieve reliable bonding fails to do so properly, leaving accessible parts at intermediate resistances to earth. (The use of rasping fasteners may produce satisfactory results on the individual device sent for type-testing, but it would appear to be difficult to consistently achieve the same result on the assembly-line) Ged Dean, Nottingham City Hospital, UK. ** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. NCHT ** --- 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
RE: chassis bonding - star washers enough?
-Original Message- From: Ron Pickard [mailto:rpick...@hypercom.com] Sent: Monday, March 25, 2002 7:28 AM To: jo...@exchange.scotland.ncr.com 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 PEM nuts may have their proper place, but I don't like to use them, since they are prone to being driven out by the pressure applied to a bolt during tightening. If the assembler just leans on the bolt a little, the nut pushes out of the clinch, and then spins in the bolt. This can turn into a bad problem if the nut is in a blind area. I prefer to use Rivnuts, which clench with a shoulder on the front surface and a deformation area on the rear. These will not fall out with axial loading. Regards, Ed Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military Avionics EMC Services Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis --- 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
RE: chassis bonding - star washers enough?
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
RE: Masking - was: chassis bonding - star washers enough?
-Original Message- From: Doug McKean [mailto:dmck...@corp.auspex.com] Sent: Monday, March 25, 2002 6:16 AM To: EMC-PSTC Discussion Group Subject: Re: Masking - was: chassis bonding - star washers enough? Very good question. In my experience, the corrosion issue with regard to masked off areas has never been a factor. Yes, it will corrode, but the teeth will cut through that. The masking off of areas has also been internal to the product. Yes, I've also used the star washers on painted areas (non-conductive paint at that) without a problem, but my *preference* is masked off areas. If you're subjecting your product to some extremes in environment other than normal office environment, then corrosion will most definitely be a concern. If you're going to use star washers on surfaces painted with non-conductive paint, then you may want to consider using a torque wrench for securing the nuts or bolts during assembly. Regards, Doug McKean The military generally doesn't like toothed lockwashers because: 1. As the teeth cut into the surface, you generate bits of paint and base metal particles. That's not nice, because the particles can cause mechanical and electrical problems. 2. Any fault current is conducted through the relatively small cross-section contact points. This can result in arcing and even vaporization of the conductive path. Look at MIL-B-5087 for typical military bonding and ground stud practices. Regards, Ed Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military Avionics EMC Services Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis --- 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
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
Re: Masking - was: chassis bonding - star washers enough?
Very good question. In my experience, the corrosion issue with regard to masked off areas has never been a factor. Yes, it will corrode, but the teeth will cut through that. The masking off of areas has also been internal to the product. Yes, I've also used the star washers on painted areas (non-conductive paint at that) without a problem, but my *preference* is masked off areas. If you're subjecting your product to some extremes in environment other than normal office environment, then corrosion will most definitely be a concern. If you're going to use star washers on surfaces painted with non-conductive paint, then you may want to consider using a torque wrench for securing the nuts or bolts during assembly. Regards, Doug McKean --- 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
Re: Masking - was: chassis bonding - star washers enough?
On Fri, 22 Mar 2002 16:53:27 -0800, Chris Wells cdwe...@stargate.net wrote: Masking As to all those who indicate masking off the metal what about oxidation? I'm concerned about the appearance of masking off the painted areas. To avoid corrosion of the exposed steel surface, plating (Zn, Ni, Cr, etc.) can be used. You can mask off only the areas of metal plates where they will be covered by the other metal plates when the enclosure is assembled (i.e. area where the metal surface will contact with the other metal surface), hence it can be designed so that it will not make the appearance poor. Regards, Tom -- Tomonori Sato vef00...@nifty.ne.jp URL: http://member.nifty.ne.jp/tsato/ xvkbd-2.2 (virtual keyboard for X) available --- 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
Masking - was: chassis bonding - star washers enough?
Thanks for all the feedback - some very good info! Masking As to all those who indicate masking off the metal what about oxidation? I'm concerned about the appearance of masking off the painted areas. Can the screw be coated after assembly? Hard to take apart for sure.. I have some problems with masking. I have no issue with the electrical/mechanical principles But it seems that the appearance will be very poor and the effort to accomplish high. I suppose that is why plated surfaces are preferred.. What about conductive paint? Too expensive? Appearance? Chris Wells Senior Design Engineer Cutler-Hammer christopherdwe...@eaton.com - Original Message - From: C From - Tue Mar 26 05:05:19 2002 Return-Path: owner-emc-p...@majordomo.ieee.org Received: from ruebert.ieee.org ([140.98.193.10]) by mtiwgwc22.worldnet.att.net (InterMail vM.4.01.03.27 201-229-121-127-20010626) with ESMTP id 20020322230554.wncj24425.mtiwgwc22.worldnet.att@ruebert.ieee.org; Fri, 22 Mar 2002 23:05:54 + Received: () by ruebert.ieee.org (Switch-2.1.0/Switch-2.1.0) id g2MN0XE08471 for emc-pstc-resent; Fri, 22 Mar 2002 18:00:33 -0500 (EST) Message-ID: 003e01c1d1f5$bc67da80$cb3e3...@corp.auspex.com From: Doug McKean dmck...@corp.auspex.com To: EMC-PSTC Discussion Group emc-p...@majordomo.ieee.org References: 001201c1d13a$2fb3b7a0$6501a8c0@chriswel 000b01c1d1ac$ba5b72e0$cb3e3...@corp.auspex.com altdp7bac3m8e...@jmwa.demon.co.uk Subject: Re: chassis bonding - star washers enough? List-Post: emc-pstc@listserv.ieee.org Date: Fri, 22 Mar 2002 15:03:10 -0800 MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4807.1700 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4807.1700 Sender: owner-emc-p...@majordomo.ieee.org Precedence: bulk Reply-To: Doug McKean dmck...@corp.auspex.com X-Resent-To: Multiple Recipients emc-p...@majordomo.ieee.org X-Listname: emc-pstc X-Info: Help requests to emc-pstc-requ...@majordomo.ieee.org X-Info: [Un]Subscribe requests to majord...@majordomo.ieee.org X-Moderator-Address: emc-pstc-appro...@majordomo.ieee.org X-Mozilla-Status: 8011 X-Mozilla-Status2: X-UIDL: 003e01c1d1f5$bc67da80$cb3e3...@corp.auspex.com John Woodgate j...@jmwa.demon.co.uk Brilliant! Next: teeth both internal and external (I've seen some, but they are very rare). And after that, quick-release bolts, so that the washer can be easily taken off for microscopic inspection and metallurgical tests. chuckle Personally John, I'm waiting for the hand-held metallurgical photo-microscopy micro-fracture x-ray scanner to be required. But I hear it's held up in the test lab due to some problems with the star washers they're using or somethin ... - Doug McKean --- 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
RE: chassis bonding - star washers enough?
Some answers to your questions: - Star washers (internal, not external) will cut through any normal paints, including powder paints. I have never seen a situation where fully tightening a screw would fail to make a good connection if an internal tooth lock washer was used. But having said that, there are those who would say that this cannot be definitely proven, and so paint masking under the screw will be necessary, if only to make people (i.e. UL etc.) feel more comfortable. - Standard internal tooth lock washers are as good as it gets. - Star washers do make a gas-tight seal when the screw is tightened properly. Light oxidation becomes irrelevant, as does re-oxidation at the contact points. - Because of the aforementioned gas-tight connection, special surface treatments are not beneficial. - PEM nuts ARE self clinching. Because they cause metal to flow under very high pressure, they make a gas-tight connection to the metal they are inserted into. Any type of PEM (or similar other brand) nut is as good as any other in this regard. The differences are in the nut part, not the way that metal is displaced when inserting. - The common type of captive lock washer screw is called a SEMS type, and is simply a normal screw with a normal internal tooth lock washer held captive by an undercut below the head. They function identically to screws with separate internal tooth lock washers. - If a lock washer is used, there is no point in using an anerobic screw locker like Loctite. Nonetheless, because of the gas-tight nature of the lockwasher interface, the use of Loctite will not affect the electrical connection between washer and screw or part. The pressure at the points of the lockwasher amounts to many tens of thousands of psi. Any liquid (i.e. loctite) will be squeezed aside. As for preferred types. Anerobic thread lockers are all essentially the same (chemically), being based on a methacrylate ester formulation. Some are more viscous, others less so; some are more reactive (harden faster) others less so, but this matters little when they are subject to the extreme pressure at the points of the lockwasher. - Use of a passivation coating like chromate conversion coating on zinc-plated steel (yellow, clear, or whatever), or Alodine on aluminum (also simply a type of chromate conversion coating) is a very good way to assure a stable interface under medium contact pressure. But its basic purpose is to ensure a consistent surface before connection is made. Since it is a sort of gel, literally mere MOLECULES thick, it is not going to affect a high pressure electrical connection in any way. It is common to hear people say that chromate coatings are conductive. This is completely false. Chromates are insulators. It is just that they are so thin that under influence of a high pressure connection, they are cut through with only minimal pressure. - Plating or coating treatments under aluminum or steel are useless as an aid to connection, since a) it is likely that it will be required to clear the paint under the screw head/lockwasher anyway, and b) the extreme pressure presented by the points of the lockwasher will cut through the coating and into the base metal. The main purpose for these coatings is paint adhesion. Proper paint adhesion to metal requires a conversion coating. For steel, phosphatizing is commonly used. For aluminum, Alodine chromate conversion is one of the common ones. For zinc or cadmium plated steel, a chromate conversion coating is used. But this is a paint adhesion issue, and as pointed out above, these have no effect on a high pressure connection. - Basically, as far as the electrical interface is concerned, plating on the screw and the lockwasher is irrelevant. The interface is gas-tight. An unplated screw will look like hell after a while, but that is another issue. When tightened, the points of the lock washer will cut through ANY plating present and make a gas-tight interface, so your plating choice should be made based on galvanic compatibility issues, not electrical connection issues. But all this above assumes that paint is masked under the screw/lockwasher interface. It is not a matter that with any paint system, and any reasonable sized screw/lockwasher (say, #6 or larger), there is no way that a good electrical connection cannot be made if the screw is fully tightened! And if the screw is NOT fully tightened, then you cannot guarantee a good connection, no matter what interface arrangement is used. It is simply that regulatory agencies are unlikely to accept this relatively obvious reality, and that they will insist that paint masking is needed. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: Chris Wells [mailto:cdwe...@stargate.net] Sent: March 21, 2002 4:40 PM To: 'emc-pstc' Subject: chassis bonding - star washers enough? Looking for some feedback on bonding various parts of a painted
Re: chassis bonding - star washers enough?
I read in !emc-pstc that Doug McKean dmck...@corp.auspex.com wrote (in 000b01c1d1ac$ba5b72e0$cb3e3...@corp.auspex.com) about 'chassis bonding - star washers enough?', on Fri, 22 Mar 2002: Thirdly, I've had some very serious discussions with some NRTL test engineers regarding external toothed star washers versus internal toothed start washers. It was *require* at one time for me to use internal toothed star washers to protect the integrity of the cutting action of the teeth to chassis. It was *suggested* at another time by another engineer to use external toothed star washers so that the integrity of the teeth could be easily inspected. Brilliant! Next: teeth both internal and external (I've seen some, but they are very rare). And after that, quick-release bolts, so that the washer can be easily taken off for microscopic inspection and metallurgical tests. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- 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
Re: chassis bonding - star washers enough?
The following is strictly my own opinion regarding star washers. Others here probably have lots more experience than I. The following is also regarding bare metal-to-metal contact only. I always require masking off around the area where grounding is done. First, the only way the grounding integrity of whatever you end up doing can be checked as being sufficient is to check it with the ground current test. Second, the integrity of the ground is highly dpendent upon the torque imposed upon the the nut or screw used for securement. Get a calibrated torque tool for the job. Thirdly, I've had some very serious discussions with some NRTL test engineers regarding external toothed star washers versus internal toothed start washers. It was *require* at one time for me to use internal toothed star washers to protect the integrity of the cutting action of the teeth to chassis. It was *suggested* at another time by another engineer to use external toothed star washers so that the integrity of the teeth could be easily inspected. My personal preferences are: 1) use only metal-to-metal contact for any sort of ground, 2) if in any doubt - test it. Regards, Doug McKean --- 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
RE: chassis bonding - star washers enough?
I will not really trust the gripping action of star washers unless such thing are custom made and fitted for their intended design. In general star washers tend to loosen their grip over time especially if the chassis has to experience some form of vibrations. This is an element of dogma... Personally I would would expect to find from a cabinet of electronic equipment running from a normal 50 Hz mains supply, a good Earth connection made to the equipment metalwork using a corrosion-resistant technique and situated close to where the mains lead enters the cabinet. All equipment metalwork should be electrically bonded in a manner which does not rely on 'hopeful' electrical conduction through anti-corrosive treatment like anodised aluminium and paint. Careful attention to the assembly process have to be done to weed out things like ball-bearings races, nylon runners and coasters, or other insulating materials. Conduction through painted panels should not be dependent on the gripping action of star washers. The design should be such that no currents flows in any part of the metal work. The objective is to ensure that any part of the metalwork can be relied upon as an effective electrostatic screen and not the reverse, a radiator regards :-) Tim Foo |-+- | | Kazimier_Gawrzyjal@Del| | | l.com | | | Sent by: | | | owner-emc-pstc@majordo| | | mo.ieee.org | | | | | | | | | 03/22/02 08:56 AM | | | Please respond to | | | Kazimier_Gawrzyjal| | | | |-+- ---| | | |To: cdwe...@stargate.net, emc-p...@ieee.org | |cc: (bcc: Wan Juang Foo/ece/staff/npnet) | |Subject: RE: chassis bonding - star washers enough? | ---| Chris, Admittedly I'm not expert on materials or on grounding principles/issues but the relevance of a rock solid bond to ground is usually beyond dispute. In a previous life, I've found star washers had a varied level of difficulty in penetrating painted materials ...it all depended on the type of paint being used. For example, the powder coat type of paint found on numerous enclosures and frames is extremely durable and you might find that star washers will barely make a dent much less provide a good bond connection. Due to the power levels involved we would make sure that bond connections were masked off as opposed to relying on a star washer for adequate bonding. At times we found they were a point of failure when conducting the Earthing test to the CSA C22.2 No. 0.4 standard as invoked by the binatcould get them glow a nice shade of red. I don't have them handy but I do recall reading some studies indicating ground connections due to the use of star washers or the like were a likely source of ignition under extreme transient eventsIEEE I think. My personal opinion and not that of my employer. Regards, Kaz Gawrzyjal Dell -Original Message- From: Chris Wells [mailto:cdwe...@stargate.net] Sent: Thursday, March 21, 2002 6:40 PM To: 'emc-pstc' Subject: chassis bonding - star washers enough? Looking for some feedback on bonding various parts of a painted metal chassis together for safety and EMC performance issues. I know we have a lot of experts out there on this topic and can remember a number of threads on the topic. Please help me pull it together: When screwing the cover on the base will star washers cut through paint, even epoxy paint and provide a reliable connection? Are there special versions of electrical star washers that work better than others? What about oxidation of the mating surface? I understand star washers can make a gas tight seal. Should there be a special treatment to the painted area where the screw/washer come together? Do PEM nuts act as a good mating mechanism for the screw? There are many types are some better than others? What about the self clenching types? One can get screws with captive washers. Are there any issues with these? Preferred Vendors and types? There are various chemical materials to keep screws from
chassis bonding - star washers enough?
Looking for some feedback on bonding various parts of a painted metal chassis together for safety and EMC performance issues. I know we have a lot of experts out there on this topic and can remember a number of threads on the topic. Please help me pull it together: a.. When screwing the cover on the base will star washers cut through paint, even epoxy paint and provide a reliable connection? b.. Are there special versions of electrical star washers that work better than others? c.. What about oxidation of the mating surface? I understand star washers can make a gas tight seal. d.. Should there be a special treatment to the painted area where the screw/washer come together? e.. Do PEM nuts act as a good mating mechanism for the screw? There are many types are some better than others? What about the self clenching types? f.. One can get screws with captive washers. Are there any issues with these? Preferred Vendors and types? g.. There are various chemical materials to keep screws from backing out and are applied to the threads of a screw such as those from Loctite. Do these interfere or help? Are some formulas better than others? h.. Under the paint if the base metal is steel are there any treatments or plating that help? For Steel, for Aluminum? i.. If the chassis is plated steel instead like zinc chromate yellow. What changes? j.. Proper plating on screw and star washer? (assume painted steel) Any advice on the topic welcome! Thanks in advance! Chris Wells Senior Design Engineer Cutler-Hammer christopherdwe...@eaton.com
