Arfa Daily wrote in message
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"Ross Herbert" wrote in message
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On Wed, 23 Apr 2008 07:49:17 +0100, "N_Cook" wrote:

:W for Wood's metal for the fusible part ?
:Googling "wood's metal" AND "fusible resistor" produces nothing


Can't say I have ever heard of Wood's Metal being used for fusible
resistors in
electrical or electronic equipment. I seem to remember that a major use
for
Wood's Metal was as the fusible element in thermal break-circuit fire
detectors
used back in the 30's - 50's. They were superseded by much better
detectors.

There certainly used to be a pellet of Wood's in the 'daisy' fire
sprinklers. I don't know of that is still the case. It's a simple,
reliable,
and more to the point 'on-the-spot' and unpowered system. The lid of my
pressure cooker still has a Wood's metal pressure pressure relief valve,
which coincidentally, I replaced just last week.

Arfa



I scraped off one of a batch of 2.2 ohm 1/3W , called fusible resistors and
heated with hot air gun to 180 deg C with no fusing anywhere.
MO over ceramic construction with spiral cut into the oxide starting and
ending 1/10 way in, so highest risistance in the axial central area between
the 2 cuts in that area , so any excess current failure would be in that
section.
So little more than a standard MO resistor , but not having the continuous
spiral. The scraped off coating seemed no more than slightly olive coloured
varnish

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Diverse Devices, Southampton, England
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