>Cozy Builders:
>
>There is another way to protect electrical circuits without using
>mechanical circuit breakers and wire fuses. About a year ago I received a
>data sheet for RAYCHEM's PolySwitch Resettable Fuses. A PolySwitch will
>trip when an overcurrent condition is present. The PolySwitch will reset
>only after it has cooled and the fault condition has been corrected.
>There's no need for manual resetting or replacement. These devices are
>available with trip points as low as 0.120 amps and as high as 9 amps.
>
>Littelfuse, which makes auto fuses, has a similiar product called Positive
>Temperature Coefficient(PTC) Resettable Devices.
>
>RAYCHEM and Littelfuse both appear to be using some type of conductive
>polymer in their circuit protectors in lieu of wire links and moving parts.
>
There's at least on product on the market using these devices. I've
posted both a design review and a usenet thread which intereseted
parties may read at <http://www.aeroelectric.com/xpbusthd.html>
and <http://www.aeroelectric.com/expbusad.html>.
I and several dozen other folk at Lear and Beech have look at these
devices several times over the last 15 years and still don't have a
way to apply these devices for general power distribution tasks
that satisfies our desire for positive protection and annunciated
faults. The polyswitches are packaged to mount inside a product . . .
soldered to an etched circuit board. The EXPBus does exactly that.
The problem is that manufacturing costs for utilizing the Polyswitch
make it more expensive to install and drives up parts count.
Bob . . .
AeroElectric Connection
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