I would like to 2nd Tim’s point of view and add that you don’t really, really know where some of your equipment will end up. Locations close to railways or next to elevator motors, for example, may have very intense levels of vibration.
The oddest location that I encountered was on a raised floor next to the baggage handling equipment at a major airport. The equipment nearly shook itself to death. That was certainly outside of our design considerations! I always recommend the use of locking hardware such as star washers. …Marko ________________________________ From: Barker, Neil [mailto:[email protected]] Sent: Wednesday, June 10, 2009 2:03 AM To: [email protected] Subject: Re: [PSES] lock washer in ground conduction path. Tim, I would have to disagree with you. I have seen nuts and bolts without lock washers come completely apart during normal commercial airfreight of equipment packed in transportation packaging; it is a very salutary lesson in the effects of vibration. In these days of global manufacturing and distribution, you have to assume that all equipment may be subject to transportation vibration. You should ensure that fasteners are locked (e.g. star washer) to fixed parts, that fasteners and washers are non-corrosive (plated or stainless, I prefer the latter), that correct torque settings are used, and that strain is relieved from cables to prevent them applying torque to the fastening under vibration conditions. There is generally no problem with star washers cutting through finishes, as the resultant connection should be gas-tight and not subject to degradation, although I would not use that in practice as I prefer the assurance of a completely clear area of metal. Also, if there is a finish, it will generally reduce the surface contact area (e.g. just the teeth of a star washer rather than the entire area of the compressed washer). Just my 2p / 2c worth! Regards Best regards Neil Barker Manager Central Quality e2v 106 Waterhouse Lane, Chelmsford, Essex, CM1 2QU, England Tel: +44 (0)1245 453616 Mobile: +44 (0)7801 723735 Fax: +44 (0)1245 453571 www.e2v.com <http://www.e2v.com/> P Consider the environment: do you really need to print this e mail? From: [email protected] [mailto:[email protected]] On Behalf Of Haynes, Tim (SELEX GALILEO, UK) Sent: 10 June 2009 09:12 To: [email protected] Subject: RE: lock washer in ground conduction path. Hi, For my 2 pence/cents worth You could take the view that a lock washer is not required unless the item is subject to moderate to high levels of vibration. If it is subject to vibration, then a lock washer is essential to mitigate the risk of the connection becoming loose. There should be no other form of stress on the connection, if there is likely to be, then the mitigation would be to stress relieve the connection rather than fit a lock washer. I would not allow a non-conductive finish to be present at a safety earth point and would never rely on a star washer to cut through. Although it might work, I would be worried that the situation may not remain stable throughout the product life. Regards Tim ************************ Tim Haynes A1N10 Electromagnetic Engineering Specialist SELEX Sensors and Airborne Systems 300 Capability Green Luton LU1 3PG ( Tel : +44 (0)1582 886239 7 Fax : +44 (0)1582 795863 ) Mob : +44 (0)7703 559 310 * E-mail : [email protected] P Please consider the environment before printing this email. There are 10 types of people in the world-those who understand binary and those who don't. J. Paxman From: [email protected] [mailto:[email protected]] On Behalf Of John Woodgate Sent: 10 June 2009 08:52 To: [email protected] Subject: Re: lock washer in ground conduction path. *** WARNING *** This message has originated outside your organisation, either from an external partner or the Global Internet. Keep this in mind if you answer this message. In message <of21be7abe.3aaf385e-on862575d0.005e93e2-862575d0.005f3...@amat.com>, dated Tue, 9 Jun 2009, [email protected] writes: >Of course, for the issue of mechanical stability, a washer can be >placed on the top side of the lug, and so not participate directly in >the conduction path. Some standards either require or recommend this. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk Things can always get better. But that's not the only option. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - Sent by a member of the e2v group of companies. The parent company, e2v technologies plc, is registered in England and Wales. Company number; 04439718. Registered address; 106 Waterhouse Lane, Chelmsford, Essex, CM1 2QU, UK. This email and any attachments are confidential and meant solely for the use of the intended recipient. 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