Hello all, Generally speaking, in the US, one may not use a fuse value of more than 125% of the rated current of a product. However, when I look at the application guides for fuses, they are thermally derated on a curve. One fuse type drops to 75% of its marked value when used in an 80C ambient. Another is not so severe, but none have a flat curve. This is to be expected as fuses are designed to open with RMS heating.
Here is a scenario that describes my problem: If the product has a MEASURED input current of 0.8 amps and is subsequently RATED for 0.8 amps, then theoretically, I allowed to use a maximum fuse value of 1 amp. If I select a 1 amp fuse and use it in an elevated ambient environment of 80C, it is going to reliably open at 0.75 amps, and I will experience nuisance tripping. The engineering side of me says I should use the manufacturer's derating curves and reselect a fuse at a higher value. The equation to select the fuse would be 1.25*(Rated Current)/(Fuse Derating). The answer is 1.33 amps and I would probably select a 1.25 amp fuse. This is 156% of the product rating! My problem is, I've already had one agency tell me I can't do this. Has anyone had experience on how to solve this problem? Thanks, -doug Douglas E. Powell Corporate Compliance Dept. Advanced Energy Industries, Inc. Fort Collins, CO 80525 USA _______________________________________________________________ This message, including any attachments, may contain information that is confidential and proprietary information of Advanced Energy Industries, Inc. The dissemination, distribution, use or copying of this message or any of its attachments is strictly prohibited without the express written consent of Advanced Energy Industries, Inc. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
