Thank you all for your input and tolerating the rantings of an old man (my kids don't like when I say that).
Rich: As usual you hit the nail on the head. We have a tendency to rationalize when the spirit of the standard is complied with but the hard proof of compliance is some what vague and the safety agency holds the line. I am the first to be upset when I see what I consider either inexperienced, sloppy or shoddy reviews of products with the possible compromise of safety due to the lack of the double checking we get from the safety agency review. I also get upset when the easy most obvious requirement is held to with no consideration as to the exceptions or real safety concerns. Terry >>> Rich Nute <ri...@sdd.hp.com> 02/20 3:36 PM >>> Hi Kaz: Answering the question, "what's the safety concern," is a reverse-engineering process with respect to the various requirements contained in the standard. Applying the requirements of the standard to the specific construction may involve or even require interpretetation of the standard. These are two, separate activities. My point is, while a certification house engineer (and you) may enjoy a reverse-engineering discussion, he cannot judge a construction based on what he learns from reverse engineering. However, he can judge a construction based on his interpretion of the requirements. Since "small part" is not defined in the standard, application of the "small part" rule is an interpretation of the standard, and is not an application of "what is the safety concern." Likewise, whether the V-1 PWB can serve as a barrier is an interpretation. The exemption of certain small parts from the V-2 requirement may or may not have a valid rationale. Reverse engineering suggests that the qualities of "small-ness," "function," "distance" or a "barrier," (with respect to an electrical part which, under fault conditions, is likely to exceed the ignition temperature of the small part) will prevent ignition of the small part. Or, that if ignited, will not contribute sufficient fuel to spread the fire within the equipment. Unfortunately, the reverse engineering that I have stated above, is also an interpretation. And, it is quite wrong from a thermodynamics point of view. Anyone who has lit a campfire knows that it is much easier to ignite small units of fuel than large units of fuel, and that the burning small units of fuel ignite the large units of fuel. Many of the requirements in our safety standards are the result of inverting a bad experience. That inversion of a specific bad experience is then generalized. The generalization makes reverse- engineering to the specific bad experience almost impossible. Those of us who are manufacturers always object to anything found by a certifier that causes us to change the product. In this case, the certification house has taken a position that the stand-off must be V-2. Establishing traceability of flame-rating of a stand-off may be quite difficult or impossible. So, we seek a way out. Most often, we either attack the certification house or we seek a favorable re-intepretation. Attacking the certification house never works (and THAT is the voice of experience). Discussion can be very effective at arriving at a favorable re-interpretation. But, while the discussion may involve some degree of "what's the safety concern," the decision must be one of interpretation. Where the interpretation remains unfavorable to the manufacturer, testing always proves (or disproves) the hypothesis. Best regards, Rich > Rich, > > As always, you've succinctly provided the full story on an approach that in > this case, will work to get Terry's product approved. I think your > interpretation of my suggestion of asking "what's the safety concern" is a > bit off however. > > Personally, I'd rather have a 5 minute conversation first before taking the > time to run the tests right away. It's possible the agency rep. may not be > all that familiar with the product and so is simply going by the book on > default (or what he/she's advised to from more senior staff), thereby > eliminating the application of engineering judgment in those areas open to > interpretation...a discretionary thing. > > By asking the question, both parties will bring to light the exact concerns > raised in the course of this particular product approval. While it's true > that a safety certification agency certifies a product to a given standard, > it's the interpretation of that standard's requirements by the parties > involved that have raised many an interesting discussion I'd wager. In my > own view, engineering judgment is not only to be used by a safety agency > rep. when applying the requirements. How else does one raise questions > which might result in an interpretive dispute but also deal with such > disputes? > > By the way, the exemption also applies to materials separated by a solid > barrier of V-1 or better (60950 ed.2), which might also be the case > here....depends on whether the stand-off falls into a "small part" criteria > as agreed upon by the agency. > > My opinion and not that of my employer. > > Regards, > Kaz Gawrzyjal > kazimier_gawrzy...@dell.com > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org