PSNet
UL Practical application guide discussion Several good points have been made in the discussion of the practical application guide supplied by UL; I’ll add my U$ two-bits worth here Let's start with a story: the question of interpretation has been with us for a long time. An old timer, a German trained engineer who later worked for a test house, described his indoctrination into the world of safety testing. As a beginning engineer, one day his boss came to him and said when they go up to VDE to have the product examined he should remember to take along his copy of the standard and make notes in the margin as to the interpretation of requirements as they were described. Later, as a project engineer, when he took his product to VDE his boss reminded him to take along the new engineer with his copy of the standard to do the same thing. This was obviously training by apprenticeship. Having worked in standards development arena for 25 years or so, I found that is not easy to make the standard absolutely clear – there is an ongoing pressure for conciseness and compromise (since it is written by a committee - you know all the old jokes: an elephant is a mouse designed to MIL specs; a camel is a donkey designed by a committee). This means that there also is ongoing effort to get clarification of requirements and to clarify the written standard itself. We know that in large companies there is considerable discussion among designers and safety engineering professionals as to the intent and requirements of the standards. In some cases it is organized, but much is not. Much of the discussion that we have here on the PSNet is along the same lines - to provide the experience of others to help clarify the requirements or the intent of the requirements in a standard. As with the company efforts, the advent of email has gone a long way to get things written down, but not always organized in any recoverable way (RCIC not withstanding). My experience is that UL engineers are generally not familiar with the PSNet discussions. There are some formal, traditional efforts to do this clarification & codification. Some standards committees themselves work to clarify the requirements; for instance TC74/IEC 60950 has a chairman's advisory panel that will answer questions from IEC national committees (not from individuals) that are phrased in a manner that they can be answered by a simple yes/no response. On occasion the process of answering these questions has prompted a change in the standard to provide additional clarification to the issue. These answers are provided back to the IEC national committees for distribution. Within the CB Scheme the CTL (Committee of Testing Laboratories) has an internal method for polling laboratories as to interpretation of requirements or testing practice and, after discussion, providing an agreed-upon interpretation for all labs to use. This is intended to provide uniform interpretation and application of requirements and testing throughout all of the participating labs on a worldwide basis. I don’t believe that these interpretations are generally available outside the labs. Finally, UL has its P. A. G. that we've been discussing. This guide was developed so that UL engineers would provide the same interpretation of requirements from any office. It's really quite convenient that they offer this outside of the lab for use but there's no obligation to do so. Charging a nominal amount to support making this available does not, in my opinion, seem unreasonable. This could also easily be done on-line where you would be charged on a page-by-page basis (how many peeks per U$ dollar at those Russian sneak-a-peek sites - once you enter your credit card number?). Whether or not these are more than guidelines - it seems that trying to work around them is like trying to push aside the preponderance of the evidence in legal proceedings. In each case they are considered opinions from a group of knowledgeable participants in each process. It would be most convenient to find some way to combine all the interpretive information into the standard such as is done with the US NEC (National Electric Code) Handbook. In that book each clause is followed by interpretive information to further explain the application of the requirements. (Hmmm – on reflection this looks like it would be a good retirement project for me if I could get my hands on the interpretations. What would you be willing to pay?) I hope that this little summary is useful. br, Pete Peter E Perkins, PE Principal Product Safety Consultant Tigard, ORe 97281-3427 503/452-1201 fone/fax p.perk...@ieee.org ------------------------------------------- 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: Michael Garretson: pstc_ad...@garretson.org 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://www.rcic.com/ click on "Virtual Conference Hall,"
