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Re: Europa-List: Electrical questions

Subject: Re: Europa-List: Electrical questions
From: n3eu@comcast.net
Date: Fri, 12 Dec 2003 21:00:45

Jos Okhuijsen wrote:

> Do i take it you have something against fuseble links?

Not really, just against Tefzel insulated wire as a fusible link verses what you
should use, or in an application where only a 25-cent fuse is needed.  Tefzel
can explode violently.

> Yes, it will explode. So will fuses, circuit breakers, switches, anything
> if you feed sufficient current through them.

Just moments ago I fed several hundred amps across a 25A automotive blade fuse.
No fun! It faintly but audibly clicked; the translucent plastic is not even
discolored. How do I make it explode?

> No, fusable links do not replace circuits breakers, but can do a very good
> job in fire protection, especially in case of a crash.

Actually fusible links do replace CB's, in high-current apps due to relative 
cost.
I don't understand the safety problem, if you're talking a wire-type fusible
link vs. a fuse or CB.  Interesting, though, that auto mfrs are tending toward
battery terminal clamps which are also a fusible link.  It would be possible,
though more likely in a metal airplane, where a shorted battery cable as
a result of a crash could start a fire not otherwise occurring.  Such technology
hasn't reached production airplanes yet.

> There is no such thing as response time,

It's rather called the time/current curve, published for all circuit protection
devices, and it governs the design selection among fuses vs. fusible links, vs.
CB's.  You could win a bet from many people by insisting they can't pop a 5A
breaker with 6 amps.  They won't see a need to wait out the time it will 
probably
take to do so.

Regards,
Fred F.




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