Rich, I like your analisys! I agree completely.
You may recall that my initial opening statement was that there is no intelligent answer (at this time?). What I find really curious is the "official" 1 minute interpretation. How are we supposed to actually apply this? I mean, UL/CSA fuses are calibrated down to 2 min (not 1). So we can't approve the circuit just by inspecting the fuse value; we must perform tests. But these fuses will open after a MAXIMUM of 2 min. There is no guarantee that they won't open much faster. In fact the very same fuse is allowed by the standards to open after 5 (or 12) seconds, depending on the batch or the manufacturer. What I'm getting at here is that we may perform a test using, by unfortunate coincidence say, one particular fuse sample that just happens to be on the fast side. (A devious manufacturer may even be able to select such a fuse on purpose, just for the safety tests -- nobody on this exalted forum, of course! :-). But the actual production samples will each have fuses that may vary widely in opening time. So I can imagine a scenario where we will run the test and the fuse opens in 5 seconds and then everything is declared safe and hunky dory. But the production units have fuses that open in anything up to 2 minutes. Seems to me that our testing was completely meaningless! Are we supposed to run the same test 2 dozen times (like when we certify a fuse)? So it appears that we can't approve the circuit just by inspection. And we also can't really get any reliable test results. So how are we supposed to confirm compliance to this 1 minute limit?! And never mind the 1 min limit itself. I still contend that spraying molten metal is going to happen in fractions of a second; not after 1 min. I've melted many screwdrivers during my TV and automobile repair days, and I assure you that it all happens in a flash (please, don't ask me how long is a flash!) And I also suggest that any twit that is willing to stand there for a whole minute while his finger is burning off, or while his face is getting sprayed with a nice metallic conformal coating, deserves to be crippled! :-) Egon
