Conformity Magazine - October 2007 - (Page 37)

U L 1449 “Transient Voltage Surge Suppressors” has been the safety standard for powerline surge suppressors for over 20 years, but changes to the UL1449 standard have opened the door to a viable alternative for surge suppression products. UL 1449 has recently been significantly revised, and will be introduced as a Third Edition and renamed “Surge Protective Devices.” Manufacturers will be required to be in compliance with the changes by October 2009. The focus of UL 1449 Third Edition has been on assuring the safety of products which principally used fixed clamping components such as MOVs (metal oxide varistors) and SADs (silicon avalanche diodes) as their primary surge suppression component. Since the safety testing assumes that products operate in a shunt mode and have a fixed voltage clamping element, filters which operate in a series mode and do not contain fixed voltage clamping elements, but were previously UL 1449 Listed, would be subjected to tests that are not relevant to determining the safety of the electromagnetic interference filter technology. As a direct result of many of the new shunt-mode safety tests being directed principally toward fixed clamping component technology, products which suppress surges and noise but use only electromagnetic interference filter technology have necessarily moved away from UL 1449. These products are now certified under UL 1283, since the UL 1449 safety testing is no longer relevant to the electromagnetic interference filter technology, even though a principal function of an electromagnetic interference filter may be to filter off undesirable noise and remove the damaging high frequency surge energy. The Importance of Surge Suppression A moment of reflection will show that powerline surges are nothing more than a short burst of high frequency energy, with the dangerous surge frequencies orders of magnitude higher in frequency than the 60 Hz power frequency. Therefore, a welldesigned electromagnetic interference filter should be able to remove powerline surges by filtering off the high frequency energy, noting the large frequency separation. Electromagnetic interference filter designs become much simpler for a given desired rejection as the frequency separation increases. Of course, the powerline is a low impedance, high energy environment, which puts special requirements on the design components. While a basic electromagnetic interference filter can dramatically reduce the surge voltage, modern computing systems have become increasingly sensitive, and are being used in increasingly important applications. For example: • With so much electronic equipment in operation, it is hard to determine exactly how much surge suppression is required to assure optimum protection of the various systems; • Every system is no better than the weakest link; • We know that, if the worst-case surge can be suppressed to a level at or below the power wave peak voltage, downstream equipment will be unaware a surge event occurred, so even the most susceptible products will be protected; • If surge voltage let-through can be dramatically reduced, there will be no degradation, no disruption, and no damage. With these issues in mind, the total elimination of dangerous surge energy even with the worst-case surges becomes an important design goal. Filtering to Achieve Total Surge Cancellation Since a good electromagnetic interference filter should be able to remove surge energy from the powerline, we undertook to develop a different approach to surge suppression. To assure ourselves we were addressing the worst-case situation, we first consulted IEEE/ANSI C62.41. C62.41 describes locations within a building and anticipated surge dangers at those locations. Although many UL 1449 products have Metalized Fabric Gaskets Less Than 3% Compression Set Tech-Etch manufactures a wide range of RoHS compliant metalized fabric gaskets providing excellent shielding effectiveness with very low compression forces. Shielding effectiveness of over 100 dB Nickel plating over copper substrate Surface resistivity < .02 Ohms Easy installation with Stick-on mounting Superior galvanic compatibility extends life Free Samples at www.tech-etch.com/shield ISO 9001:2000 REGISTERED TECH-ETCH, INC., 45 Aldrin Road, Plymouth, MA 02360 october 2007 conformity 37 http://www.tech-etch.com/shield http://www.tech-etch.com/shield

Table of Contents Feed for the Digital Edition of Conformity Magazine - October 2007

Contents Editor’s Note Commission Proposes Changes for 57-64 GHz Spectrum Rules FCC Continues Actions Against Jamming Device Distributors Radio Operator Fined for Failing to Make Equipment Available for Inspection Commission Fines Unsolicited Fax Advertisers Firm Offering Quality Standards Training Also Fined Breaking New Ground with Lithium-Battery Generic Requirements for Use in Telecommunications Facilities ESD Open Forum EMC UK 2007 Conference Set Staying Abreast of U.S. E-Waste Legislation EU Commission Establishes RFID Expert Group Update on China's CCC Compliance Program System Level ESD Testing: The Waveforms An Alternative Approach to Surge Suppression Testing Equipment Buyer's Guide EU Scientific Committee Releases Updated Data on EMF Risks Updated Standards List For The EU’s EMC Directive Updated Standards List For The EU’s Directives on Measuring Instruments Call for Presentations for 2008 International ESD Workshop Announced CPSC Actions In The News IEC Standards Update Product Reviews UL Standards Update New Products From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Upcoming Events Advertisers

Conformity Magazine - October 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.