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Fuse Failure

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Bob_Muzio

Jedi Trainee
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I encountered a failure of the fuse which controls the radiator
fan, horn, and brake lights on my '63 FHC. The fuse didn't fail in
the traditional way i.e. exhibiting the filament blown in the
center. As a matter of fact the fuse, a modern BUSS fuse, didn't
look blown at all. I initially checked it for continuity and it was
fine. It was only after I stuffed a new fuse in the holder and
everything worked that I went back to the fuse. After shaking it,
it then failed the continuity test, intermittantly. It has
obviously failed where the filament attaches to the end caps.
Again, there are no visual clues, like discoloration.
Any ideas? I'd like to think a bad fuse but that would be too
simple, no?
Bob
 
Hi Bob, that's not too far fetched. My dad has a small plane, and he has had a couple of fuses fail in it just from age and vibration. Seems the fuses were mounted so the thin blade was horizontal, and eventually bowed down over some 30 years. So he's had to replace a couple without actually having them burn out.
 
[ QUOTE ]
I'd like to think a bad fuse but that would be too simple, no? Bob

[/ QUOTE ]
No -- Sometimes a connection between end cap & fuse element just comes apart. Vibration, bad factory connection. The old design Lucas fuses & others are subject to this if the end caps ever get twisted on the glass.
D
 
Since posting the concern a friend indicated that this failure is not uncommon. It seems that one can damage the fuse by twisting it in the holder when one installs it.
Bob
 
Yup - Buss, Littlefuse, & other US made fuses have a noticeably stronger bond between glass & end caps. Even better brand fuses can have a few bad ones slip through. For some reason, Lucas knockoffs & some Chinese fuses are noticeably weaker mechanically.

If you are wondering, you can replace Brit fuses with US fuses. Due to different rating systems, Brit fuses & US fuses will have different numbers for APPROXIMATELY the same ratings.

Brit (Lucas)--------US (SFE AGC)
5-----------------------3
10----------------------5
20---------------------10
25---------------------15
30---------------------15
35---------------------20
50---------------------25
Later Lucas fuses are dual marked to eliminate some of the confusion. An example is the 17/35. In this case the 17 is the approximate continuous current carrying capacity & 35 would be the fast blow rating.
This means that a single marked 35 or a dual marked 17/35 amp marked Lucas fuse is about the same as a 20 amp marked BUSS fuse.
D
Edit:
The US ratings are the continuous current carry ratings. In this case the Lucas fuse marked 35 or 17/35 would have a continuous rating of 17 & the US 20 rating would be close with it's continuous rating of 20.
D
 
hey, those fuse rating equivalents are great, I've always wondered about that subject, never finding any info. All I hope is that they are correct, because I plan to use the chart for my Jags. Also, it's true that European fuses have weak and sensitive connections from one end to the other, I prefer the American fuses.
/ubbthreads/images/graemlins/iagree.gif
 
"I only hope they are correct"-Take it from me they are!---Keoke
 
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