A boating neighbor checked my interior boat temperature a few days ago and
found it at 32 degrees...my Webasto was not working...It was in the teens
outside but salt water had not frozen...

Upon arrival I found a 30 amp AGC fuse with an end solder melted....(no
freeze damage) ....I replaced it with the same size since AGC don't come any
bigger and was aboard 3 days....the Webasto worked  fine and sounded normal.
This same fuse has been in operation for three years 11 months...I estimate
current draw at 19 amps and plan to measure it...Meantime, To cut current
draw a bit, I shut off two fan heaters...there is still plenty of  heater
capacity.

Question: Have any listees had suspicious AGC fuse "failures"??
I inspected this fuse and in line holder and while the ends were not brand
spanking shiny new, they were dull rather than corroded....could this be
enough to generate a little resistance and heat??? I have a two way switch
and am thinking about using my alternate power source which is fed through a
modern circuit breaker...

Cheers,
Rob Brueckner

Rob Brueckner askd:
Question: Have any listees had suspicious AGC fuse "failures"??
I inspected this fuse and in line holder and while the ends were not brand
spanking shiny new, they were dull rather than corroded....could this be
enough to generate a little resistance and heat??? I have a two way switch
and am thinking about using my alternate power source which is fed through a
modern circuit breaker...

REPLY
Yes indeed!

Last month I replaced a whole fuse block with 20 fuse positions for that
reason.
The metal clips wer not corroded but had a dull finish  and was discolored.
A check with my IR  thermometer revealed two of the contacts measured a 91
Celcius while several measured 60 Celcius.
A further check  showed only 4 amps flowing the the hottest fuse clip. The
fuse was 15 amp.

The spring clip had relaxed enough to cause increased resistance.
The increased resistance caused further oxidation(tarnishing) and so on.

Left unchecked this is how "mysterious" electrical fires get started.

An elevated clip temp plus an internal temp rise from a start surge is
enough to melt the low temp element inside the fuse holder.

For this reason I like to do a full load temp check on electrical panels
once a year.

regards
Arild

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Rob,
AGC glass fuses are available up to 35 amps, though over 30 are
hard to find.  You might also find a 30 amp slo-blo, which will
help with fan starting loads.

I suspect that the slight tarnish you saw did indeed cause slight
heating of the fuse.  A hot fuse will blow at lower current,
being a thermal device.

=====
Mark Richter, M.E., aboard M/V Winnie the Pooh,
"Mark's Mobile Marine" electrical systems repair & consulting.  Homeport Stuart, FL  Verizon cell 772-631-7408, free after 9PM & weekends.

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