Resistor/Fuse replacement (DEC H7104-D)

drlegendre . drlegendre at
Tue Mar 22 22:56:46 CDT 2016

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


On Tue, Mar 22, 2016 at 10:20 AM, Vincent Slyngstad <
v.slyngstad at> 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

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