Vincent & All, Yes, I read that the series conforms to that particular UL fusing requirement. My point was that I didn't see any promotion of or expansion on the fusing qualities of the design. The UL spec almost seemed like an afterthought. But then, I am not an engineer - so not used to parsing these documents to such a level.
But you comment on fire prevention is duly noted. As the saying goes, "the transformer fails open to save the fuse" ;-) As for a resistor + fuse in series, I suspect you'd want to spec the fuse for allowable currents - and then spec the resistor to withstand any current in that range. Point being, you only +need+ one 'weak link' in the design. Thoughts? On Tue, Mar 22, 2016 at 10:20 AM, Vincent Slyngstad < v.slyngs...@frontier.com> wrote: > From: drlegendre: Monday, March 21, 2016 6:50 PM > >> I don't quite get what makes this DigiKey part suitable for the role of a >> fused resistor. I do see that it has specs for 'fusing behavior' but that >> aside, I don't see that this series is marketed / sold as a "fusible >> resistor". >> > > I take "UL1412 recognised fusing" (sic) on the first line of the data sheet > to mean that they do market them that way. > > One reason I question it, is the fact that the fusing ratings are only >> plotted for like 40X or 50X expected current. Can the circuit under >> protection be relied upon to produce those levels of current, even under >> hard-fault conditions? >> > > I read a little over 1000 seconds to fuse at 10W, which is only a few > times the 2W rating. Admittedly, 20 minutes at 5X load amounts to a pretty > slow fuse. I can only assume their concern is fire prevention, rather than > circuitry protection. > > With regard to the suggestion of a fuse and a resistor, you'd need more > room (likely not a problem), and a flameproof version of the resistor. I > don't know anything about UL ratings, so I don't know if that could be made > OK there or not. > > Vince