hello Brian,
As far as your concerns to safety, you are right. In service areas (EN 60950) no concern exists for mechanical safety. Electrically there are some restrictions, that can be overcome using interlocks or covers. Your conclusions about the effectiveness of BeCU finger stocks is directly related to the conductivity of the material. The screening efficiency of a Faraday cage is directly related to the XYZ conduction of its material. As contact surfaces usually are the highest impedances in the round-going current path on the enclosure's surface, the contacting qualities are of major importance. You may consider also separating skin-effect currents on the inside surface of the enclosure (induced here by inside generated radiated H-field) and the skin-effect current on the outside of the enclosure (caused by h-fields externally of the enclosure). This requires careful design of the enclosure. These measures might be out of your control, but the recommendation might be useful to others. Regards, Gert Gremmen == CE-test, qualified testing, Consultancy, Compliance tests for EMC and Electrical Safety 15 Great EMC-design tips available ! Visit our site : http://www.cetest.nl The Dutch Electronics Directory http://www.cetest.nl/electronics.htm == -----Oorspronkelijk bericht----- Van: f...@netc.ie [SMTP:f...@netc.ie] Verzonden: woensdag 18 maart 1998 13:29 Aan: emc-p...@majordomo.ieee.org Onderwerp: FW: EMI gaskets - Subject: EMI gaskets I am interested in hearing the experiences of anybody out there who has had a need for using EMI gaskets, in particular between metal faceplates of circuit packs in a Telecomms Sub-rack. We have evaluated BeCu finger stock and foam covered with a metallised fabric and have found the metal fingers out-performed the foam. But, due to customer complaints relating to safety hazards posed by the metal fingers we are being pressured to use the foam. Has anybody else faced similar problems ? >From our experience, if the fingers are designed suitably for the application and applied correctly there should not be a hazard. My reading of IEC950/EN60950/UL1950 does not indicate any prohibitive clause relating to metal fingers. The closest (4.1.4) only stipulates protection of the OPERATOR and does not refer to SERVICE PERSONNEL, who would be the only persons exposed to the risk i.e. it is only when a module is withdrawn from a shelf that the fingers are exposed (our equipment is Central Office type). Does anybody know of any safety/regulatory objective reasoning for not using fingers, if correctly designed-in, in an application such as ours ? Regards, Brian McAuliffe Regulatory Engineering Tellabs Ltd Tel: +353.61.703269 --openmail-part-000dead1-00000001 --openmail-part-000dead1-00000001--
