22 Mar
2016
22 Mar
'16
8:56 p.m.
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.slyngstad at 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