Jim - Except for when a high breaking capacity fuse is needed, arc extinguishing fillers, like sand, are not generally necessary. I would also expect that such a fuse would not be in a primary circuit, where the US safety standard expects a fuse to see 10kA for miniature fuses. Even most of these fuses (again, in the US) don't use arc extinguishing fillers, but are simple glass tubes with metal ferrules (the 1" by 1-1/4" miniature fuses, and even several varieties of 5mm by 20mm fuses).
The above is based on my experience testing fuses for about 4 years, during my tenure at UL. Regards, Peter L. Tarver, PE ptar...@nortelnetworks.com -----Original Message----- From: Jim Freeman In all of this discussion, no one has mentioned the possibility of fire from blowing a PCB trace fuse. I know that there are flame retardants in the PCB material that protect to a certain flashpoint but to rely on that mechanism for fire prevention is a bit far fetched. From my limite experience with fuses, there is generally a large structure that is enclosed in sand to prevent a fire from spreading. Jim Freeman Peter Tarver wrote: My experience with safety agencies is they do not want to rely on traces opening to act as fuses and no standards have been developed, that I am aware of, to address this issue. Fuses certification gets involved in the metallic alloys used, to the fraction of a percent, the conductor size, additional construction features, such as heat sinking elements for time delay characteristics, tension loading for fast action, blah, blah, blah. Most of these issues are far too difficult to control for pwb traces, especially considering the etching processes don't lend themselves to the level of control necessary to be a reliable fuse of specific ratings. Additionally, the heat sinking from pwb layout of one product to another or varying copper thicknesses in a product line, adding or subtracting ground planes for emc, the variability of soldering processes and location/thermal capacity of components on the pwb make this seem far too cumbersome to want to work with. BTW, this is a very different world from "repeated twice, same result" single-fault testing, where a pwb trace opens. Regards, Peter L. Tarver, PE ptar...@nortelnetworks.com -----Original Message----- From: Matsuda, Ken [mailto:matsu...@curtisinst.com] Sent: Thursday, September 14, 2000 7:02 AM To: emc-p...@ieee.org Subject: PCB fuse trace I was wondering if anyone knew a standard for the US, Canada, and Europe that covers PCB board traces that can be used as fuses? Thanks for the help, Ken
