Re: Small 1000-4-3 chamber
In Test Measurement Europe magazine (May 1997) there is a good article by David Marsh titled -Test Cells Monitor Immunity or Emissions-which covers using small test cells for immunity testing. Different manufactures are discussed and a table is shown with manufacturers basic specs etc. Hope this helps Tony O'Hara EMC Sales Engineer, Colorado
Bonding of structures
I have a projector assembly which is essentially a large metal structure (frame) with a metal projector platform which swivels for purposes of maintenance. The structure is painted steel, with pressed in bronze bushings at all motion points each of which have been measured at significantly less than 0.10 ohms. Arguably, there is no guarantee that these structures will remain bonded at these levels over time and bonding wires (braid, with crimped ring lugs) have been added across the pivot points. These wires are secured to the structure using a toothed washer and screw. The intent of the toothed washer is to bight through the paint to ensure conductivity. My customer's safety officer (in Europe) is now insisting that the paint must be ground off to bare metal and coated with Zinc paint prior to affixing the lug to the structure. I am concerned that this is an excessive requirement. It has been my understanding that the toothed washer (and the screw for that matter) creates a gas tight connection which is acceptable for all bonding requirements. I would be interested in hearing from the group regarding this bonding issue. I can find no standard or specification which disallows this biting washer or requires Zinc paint. Any comments would be appreciated. Rick Busche rbus...@es.com
Re: Bonding of structures
Rick, It took a while to find, but page 19 of CSA Technote TN-017 dated Jan. 13, 1993, covers the construction which you describe. I suspect that CSA C22.2 No. 0.4 also covers the construction, but I don't have a copy of that standard (I shouldn't admit to that should I !!! ). The Technote states: If the metal surface is painted, it shall be scraped to remove paint at point of connection (masking is recommended while paint is applied.). In lieu of scraping, a star-toothed washer (not a split type lockwasher) may be used between the lug (or eyelet) and the metal to pierce the paint of equipment used on circuits fused at 15 A max. etc. So your construction should be acceptable if it is connected to a 15 A or less branch circuit. If rated higher than that, you could resort to the test described on the referenced page 19 for circuits rated 20 A and greater. I think that you could even run the test on the complete assembly rather than test each bond individually. I've FAXed you a copy of that page, but I recommend that you get a copy of the entire Technote and also C22.2 No. 0.4 from CSA. Gabriel Roy (21) Personal opinions expressed only, not corporate (thank heaven). Rick Busche wrote I have a projector assembly which is essentially a large metal structure (frame) with a metal projector platform which swivels for purposes of maintenance. The structure is painted steel, with pressed in bronze bushings at all motion points each of which have been measured at significantly less than 0.10 ohms. Arguably, there is no guarantee that these structures will remain bonded at these levels over time and bonding wires (braid, with crimped ring lugs) have been added across the pivot points. These wires are secured to the structure using a toothed washer and screw. The intent of the toothed washer is to bight through the paint to ensure conductivity. My customer's safety officer (in Europe) is now insisting that the paint must be ground off to bare metal and coated with Zinc paint prior to affixing the lug to the structure. I am concerned that this is an excessive requirement. It has been my understanding that the toothed washer (and the screw for that matter) creates a gas tight connection which is acceptable for all bonding requirements. I would be interested in hearing from the group regarding this bonding issue. I can find no standard or specification which disallows this biting washer or requires Zinc paint. Any comments would be appreciated. Rick Busche rbus...@es.com
RE: Bonding of structures
Rick Busche wrote: I have a projector assembly which is essentially a large metal structure (frame) with a metal projector platform which swivels for purposes of maintenance. The structure is painted steel, with pressed in bronze bushings at all motion points each of which have been measured at significantly less than 0.10 ohms. Arguably, there is no guarantee that these structures will remain bonded at these levels over time and bonding wires (braid, with crimped ring lugs) have been added across the pivot points. These wires are secured to the structure using a toothed washer and screw. The intent of the toothed washer is to bight through the paint to ensure conductivity. My customer's safety officer (in Europe) is now insisting that the paint must be ground off to bare metal and coated with Zinc paint prior to affixing the lug to the structure. I am concerned that this is an excessive requirement. It has been my understanding that the toothed washer (and the screw for that matter) creates a gas tight connection which is acceptable for all bonding requirements. I would be interested in hearing from the group regarding this bonding issue. I can find no standard or specification which disallows this biting washer or requires Zinc paint. Any comments would be appreciated. Rick Busche rbus...@es.com Reply: You may have already thought of this but... My approach to this kind of requirement is to respectfully ask the customer to cite the language in the standard that requires this construction. If they are unable to provide this reference, I would ask if they have a specific requirement for this construction method other than a standard. If they still cannot supply you with a good reason, I would have to say that you can decline their request. Bear in mind that these folks are your customer and this may be an unspoken expectation on their part. If it is something they are willing to pay for and you can charge them for it, it may be desirable to do. I learned long ago that if I cannot cite the standard that is the basis for my requirement (or finding in the case of auditing), I don't insist on having it my way. Regards Bob Collier Graphics Microsystems bcoll...@gmicolor.com Nobody pays me for these opinions, perhaps there is a reason...
Re: Bonding of structures
Rick, I can't speak for any of the Euro-Norms, but in aerospace an internally-toothed ring terminal is generally considered adequate. That said, I believe that a toothed washer will provide the function that the customer wants, but it's hard to tell. Are they concerned about some sort of really harsh (salt spray, acid, etc.) environment? If so, then some sort of sealer should be applied to each joint after assembly. As always, these are my views only and they're probably wrong! Steve Chin StreamLogic Corp. Menlo Park, CA, USA sc...@streamlogic.com Rick Busche (rbus...@es.com) wrote: I have a projector assembly which is essentially a large metal structure (frame) with a metal projector platform which swivels for purposes of maintenance. The structure is painted steel, with pressed in bronze bushings at all motion points each of which have been measured at significantly less than 0.10 ohms. Arguably, there is no guarantee that these structures will remain bonded at these levels over time and bonding wires (braid, with crimped ring lugs) have been added across the pivot points. These wires are secured to the structure using a toothed washer and screw. The intent of the toothed washer is to bight through the paint to ensure conductivity. My customer's safety officer (in Europe) is now insisting that the paint must be ground off to bare metal and coated with Zinc paint prior to affixing the lug to the structure. I am concerned that this is an excessive requirement. It has been my understanding that the toothed washer (and the screw for that matter) creates a gas tight connection which is acceptable for all bonding requirements. I would be interested in hearing from the group regarding this bonding issue. I can find no standard or specification which disallows this biting washer or requires Zinc paint. Any comments would be appreciated. Rick Busche rbus...@es.com
Re: Bonding of structures
Rick: I would assume that the main concern is damage to the protective paint layer which gets ripped open and may give access to moisture with potential for corrosion. That is, if you paint the bare steel without any protective coating. If you used zinc plating (or similar) in the first place, no question should arise, although damage to the plating due to the bite of the washers and possible damage to the plating due to slippage of the washer may keep the debate going.. You are right in assuming that the toothed washer provides gas-tight contact (specify a minimum torque requirement before this can gets opened!) but in my opinion, damage to the paint would negate this over time. The way I see it, the question boils down to money (as usual): are you willing to engage in a protracted argument my expert vs. your expert, or would it be cheaper to not paint the areas of concern and provide some selective plating? Another cheap way would be to put some spray paint on the screws after everything has been tightened down, which may lead again to arguments as above. Please let me know how this ends. Bogdan M. Matoga bogdan.mat...@fibre.com __ Reply Separator _ Subject: Bonding of structures Author: Rick Busche rbus...@es.com at Internet List-Post: emc-pstc@listserv.ieee.org Date:6/2/97 16:43 I have a projector assembly which is essentially a large metal structure (frame) with a metal projector platform which swivels for purposes of maintenance. The structure is painted steel, with pressed in bronze bushings at all motion points each of which have been measured at significantly less than 0.10 ohms. Arguably, there is no guarantee that these structures will remain bonded at these levels over time and bonding wires (braid, with crimped ring lugs) have been added across the pivot points. These wires are secured to the structure using a toothed washer and screw. The intent of the toothed washer is to bight through the paint to ensure conductivity. My customer's safety officer (in Europe) is now insisting that the paint must be ground off to bare metal and coated with Zinc paint prior to affixing the lug to the structure. I am concerned that this is an excessive requirement. It has been my understanding that the toothed washer (and the screw for that matter) creates a gas tight connection which is acceptable for all bonding requirements. I would be interested in hearing from the group regarding this bonding issue. I can find no standard or specification which disallows this biting washer or requires Zinc paint. Any comments would be appreciated. Rick Busche rbus...@es.com
CB Sheme - Body One and Body Two ...
Specifically, what are Body One and Body Two organizations in the CB scheme?
Re: Class I laser . U.S. vs EN 60825
Bob, to reply quickly, Not speaking for Cisco, and not having any specific knowledge of that product or that approval, and without checking the 2 spec's for comparison at this time... I'm recalling that the measurement aperture size is different for the 2 spec's (10mm vs. 15mm??), so even if the pwr limits may be the same at a given wavelength, for classification, the measurement is, I believe, performed differently, thus - different measurement values can be obtained for the same product per the 2 different specifications. I'm sure someone here will look into this deeper Best regards, Stephen C. Phillips These opinions are my own, and not those of Cisco Systems. At 01:18 PM 6/2/97 -0400, you wrote: I came across a safety notice from Cisco indicating that under a certain failure mode one of their single Mode FDDI cards will exceed EN 60825 limits for a class I laser device, but still meet U.S. limits. I thought the limits were the same. Can anyone explain? Robert Brister EHS Senior Associate Digital Equipment Corporation (508)493-8141 FAX:(508)493-8353
Copy of: Bonding of structures
-- Forwarded Message -- From: Chris Dupres, 100014,3703 TO: Rick Busche, INTERNET:rbus...@es.com DATE: 6/3/97 7:03 AM RE: Copy of: Bonding of structures Hi Rick. You wrote about earthing screws etc.: The intent of the toothed washer is to bight through the paint to ensure conductivity. A few years back, on a Machine Control Panel door, we used such an earthing screw method (Screw, crimped terminal ring, toothed washer, painted panel, spring washer, nut). For whatever reason, the main incomer cable had one phase wire come out of the main isolator and it sprung back and touched the panel door inside. We know this because the location of the Earth bolt was now a very badly burnt hole, and no sign of the toothed washer. The opinion at the time was that the washer itself took the whole of the fault current, and being high carbon steel, was high resistance, and got so hot that it caught fire! (hold a guitar string in a gas flame and see what happens!) Also.. The initial heating of the washer annealed the 'spring' of the washer, which collapsed, therefore reducing contact pressure and giving rise to an arc which simply burnt back like an arc welder with a high carbon steel rod. Initial heating is excacerbated because the point contacts of the teeth have very poor thermal conductivity to the steel case, and therefore any overheating due to I2R wont be dissipated into the case metal. I've come to the conclusion that star/toothed washers for protective earthing purposes are intrinsically poor, and bound to fail when you need them most. A spot faced surface and a ring terminal with NO intermediate washers, but a flat spring or wavy washer on top of the crimped terminal ring is almost infallible, and a welded stud is far superior to a bolt/nut, as the fault current can also find it's way through the wavy washer/nut to the stud. Subsequent tests with a car battery (Hardly precision, but informative) showed that star washers failed at about 25A, and flat spot faced contacts didn't fail, but the cable caught fire! Re. the zinc paint. I don't think thats a very good idea... zinc paint is paint, with zinc in. Zinc paint, while being conductive, is fundementally metal in a resin matrix. Not the sort of material that makes a good fault path. Just put a sticky round label over the screw hole or run a screw into the hole prior to painting. Star washers seem to be fine for EMC/noise/RF grounding purposes. Just a humble opinion from a chap who has to take the blame for brand new machines catching fire and people getting electric shocks from machines. Chris Dupres Surrey, UK.
